Botulism and home canning

In certain types of food preservation such as canning, an illness called “botulism” is a concern and the preservation techniques must provide a way to control for it.

One of the reasons authorities focus on controlling botulism in home canning is that when you institute controls for it, you’ve also conveniently dealt with a whole host of other possible biological nasties. So it’s quite handy to just control for the one thing.

If you follow tested recipes and approved procedures for safe home canning, you don’t need to think about botulism or even read this page, because reputable sources build massive margins of safety into their recipes. (See the USDA’s safety margins for home canning.) But if you are interested nonetheless, here’s some basics about botulism and food, boiled down to plain, simple English.

See also: Botulism from home canning in the United States

What is botulism?

There are  three aspects to the bacteria that causes “botulism”:

1. The actual bacteria that gives birth to the spores;
2. The spore that creates the toxin;
3. The toxin

[Ed: Note that technically “botulism” is of course the illness that people contract. Below, that term may be used in several places in lieu of otherwise more correct but clinical and unfamiliar Latin terms, in an attempt to keep this as layman accessible as possible.]

Botulism is not contagious; nor is there any vaccine against it.  ^[1] Actually, there is “an investigational vaccine that is available only to laboratory people working with Clostridium botulinum or the toxin.” Botulism. Communicable Disease Control and Prevention, San Francisco Department of Public Health. Accessed July 2015.   ^[2] “A vaccine that has been approved by the Food and Drug Administration (FDA) for use in clinical trials on humans. However, investigational vaccines are still in the testing and evaluation phase and are not licensed for use in the general public.”  CDC Glossary. Accessed July 2015 https://www.cdc.gov/vaccines/about/terms/glossary.htm.

1. The actual bacteria

The actual rod-shaped bacteria is called “Clostridium botulinum.”

It is not a problem itself in the grand scheme of things. The bacteria in its rod form can’t hurt you.  Which is a good thing because, even though the bacteria is particularly in soil, it’s everywhere:

C. botulinum is …. widely distributed in soil, sediments of lakes and ponds, and decaying vegetation. Hence, the intestinal tracts of birds, mammals and fish may occasionally contain the organism as a transient.”  ^[3]  Todar, Kevin. Todar’s Online Textbook of Bacteriology. University of Wisconsin, Department of Bacteriology. Accessed July 2015. 

The bacteria form is often particularly found in honey but that’s not a problem for adults because their stomach acid is strong enough to deal with it.

And, it’s a weakling.

[Clostridium botulinum] is killed by being raised to a temperature of 70 C and held there for 2 minutes.”  ^[4]”pasteurisation: 70°C 2min or equivalent” will kill Cl.botulinum bacteria.” Foodbourne Botulism. Food Safety Authority of Ireland. Accessed March 2015 at https://www.fsai.ie/faqs/botulism.html#botulism. Link gone invalid by Jan. 2018.

 2. The spores

The rod form bacteria generates spores. The spores themselves can’t hurt you, per se, either, which is a good thing, because if you get a mouthful of dust, it may have botulism spores in it, and if you eat honey, it may have botulism spores in it:

Most of the time, botulism bacteria live in an inactive form called spores. Inactive botulism spores are found widely in soil, dust, and honey. A hard coating helps the spores survive heat, drying, and radiation for long periods of time. When botulism spores enter the human body, they turn into active botulism bacteria and begin making botulism nerve toxin. Botulism toxin can also be present in foods that are not properly canned or refrigerated.”  ^[5] Botulism. Communicable Disease Control and Prevention, San Francisco Department of Public Health. Accessed July 2015.

The spores are often on the surface of produce. The USDA Complete Guide says:

Botulinum spores are on most fresh food surfaces. Because they grow only in the absence of air, they are harmless on fresh foods.” ^[6]United States Department of Agriculture (USDA). Complete guide to home canning. Agriculture information bulletin No. 539. 2015. Page 1-6.

The USDA’s Food Safety and Inspection Service writes,

C. botulinum spores are often found on the surfaces of fruits and vegetables and in seafood.”  ^[7] USDA FSIS. Clostridium botulinum. January 2010. Accessed July 2015 at https://www.fsis.usda.gov/wps/wcm/connect/a70a5447-9490-4855-af0d-e617ea6b5e46/Clostridium_botulinum.pdf?MOD=AJPERES.

That’s likely part of the background rationale for the USDA having people peel so many things before canning; to get the bacterial load down, and, the reason why fish and seafood processing times are longer than for meat.

The spores are both weak, and tough.

Botulism spores are weak

They are weak in that something simple like the acidity of strawberries, or peaches, or pickles, immobilizes them. The acid won’t kill them, but, they can’t grow (germinate) in high-acid environments and because they can’t, they can’t produce their deadly toxin (which we’ll discuss next.) [Ed: unless something happens to that food to lower the acidity of those foods, such as improper canning techniques.]

Angela Fraser at Clemson University says,

The bacteria that produces botulinum toxin cannot grow in high-acid foods…”  ^[8] Fraser, Angela. Associate Professor/Food Safety Education Specialist. How Canning Preserves Food. Clemson University, Clemson, SC. Accessed March 2015 http://www.foodsafetysite.com/consumers/resources/canning.html.

The World Health Organization says,

Clostridium botulinum will not grow in acidic conditions (pH less than 4.6), and therefore the toxin will not be formed in acidic foods ^[9] Botulism. World Health Organization Food Safety Info Sheets web site. August 2013. Accessed March 2015.

Botulism spores are tough

But the spores are tough, in that they can survive being boiled for hours and hours, maybe even days and weeks, on end. The temperature of boiling water, 100 C, is like a nice little spa day for them.

Consequently if we are taking the heat path to deal with the spores, extreme heat beyond the temperature of boiling is required.

Different authorities will give different temperature / time combinations.

At 121 C (250 F), it’s 3 minutes. Researcher N.M Anderson says,

The application of the ‘‘botulinum cook’’ is defined as equivalent to 3 minutes heating at 121 C.  ^[10] N.M Anderson et al. Food Safety Objective Approach for Controlling Clostridium botulinum Growth and Toxin Production in Commercially Sterile Foods. Journal of Food Protection, Vol. 74, No. 11, 2011, Pages 1956–1989 doi:10.4315/0362-028X.JFP-11-082. Page 1959

The Food Safety Authority of Ireland says,

To kill the spores of Cl.botulinum a sterilisation process equivalent to 121°C for 3 min is required.” ^[11] Foodbourne Botulism. Food Safety Authority of Ireland. Accessed March 2015 at https://www.fsai.ie/faqs/botulism.html#botulism6

The USDA has set a lower target temperature for most usual operations of 240 F / 115 C.

Angela Fraser at Clemson University gives the USDA approach:

The bacteria, Clostridium botulinum, form spores that can survive hours in boiling water. The good news is that these spores are easily destroyed within a reasonable time at 240°F [115 C] (the temperature reached inside a pressure canner at 10 pounds pressure [Ed: below 300 metres / 1000 feet]).”  ^[12] Fraser, Angela. Associate Professor/Food Safety Education Specialist. How Canning Preserves Food. Clemson University, Clemson, SC. Accessed March 2015 http://www.foodsafetysite.com/consumers/resources/canning.html. [/ref]

One important take-away from this is to note that regardless of the temperature / time combination that authorities are discussing, they don’t mean that the inside of your canner should reach that temperature, or that the inside of your jar reach that temperature: they mean that the coldest spot inside your jar, and right inside the pieces of food themselves at that coldest spot, should reach that temperature for the specified period of time to ensure that the resistance of the most deeply hidden botulism spore is overcome. That’s why heat penetration and circulation studies are done.

3. The botulism toxin

The botulism toxin is actually called the “botulinum” toxin in technical terms.

We established the first two aspects of the bacteria don’t hurt you, per se (except inasmuch as they of course lead to this.) This third aspect will.

The toxin is released as the spores germinate to turn into rod bacteria.

It’s one of the most deadly toxins known, ever. In fact, just about the only toxin deadlier than the regular Botulinum toxin is Botulinum toxin type H-. It’s so deadly, that scientists won’t even publicly release the DNA of it.  ^[13] Botulinum Toxin type H- the Deadliest Known Toxin With no Known Antidote Discovered. Nature World News. 15 October 2013. Accessed July 2015. 

This is why the USDA is so afraid of it. Elizabeth Andress, head of the National Center for Home Food Preservation and a frequent USDA collaborator, writes:

The botulinum toxin, one of deadliest known, causes botulism food poisoning. 1 mg can kill 655 tons of mice. Food can contain toxin without showing signs. An antitoxin is available, but there is slow recovery. Permanent nerve damage is possible.”  ^[14] Andress, Elizabeth L. Pressure Canning and Canning Low Acid Foods at Home. Cooperative Extension: University of Georgia. Powerpoint presentation, slide 7. Accessed March 2015 at nchfp.uga.edu/multimedia/slide_shows/CanLowAcid_web08.ppt.

Inside you, the toxin essentially paralyses you to death by shutting down your nervous system. Eventually, the muscles required for moving the lungs for breathing cease functioning, and the patient, if still extant, requires an iron lung.

Botulism Treatment

Botulism is treated with an anti-toxin.

The botulism antitoxin is made in Canada. It covers all seven known botulinum nerve toxin types (A, B, C, D, E, F, G). [Ed: note from above, though, that a new eighth type H has been described.  ^[15] MacKenzie, Debora (14 October 2013). “New botox super-toxin has its details censored”. NewScientist. Accessed July 2015. https://www.newscientist.com/article/dn24398-new-botox-supertoxin-has-its-details-censored.html ] It is kept in secure locations, to keep it from the hands of terrorists.  “It is stored in the Strategic National Stockpile and distributed through the CDC’s Drug Service.”  ^[16] FDA News Release. FDA approves first Botulism Antitoxin for use in neutralizing all seven known botulinum nerve toxin serotypes. 22 March 2013 at https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm345128.htm.

The antitoxin usually has to be flown in to the location needed.  It is stored frozen and requires 14 hours to thaw.  It is delivered to the patient as an intravenous drip. “The antitoxin is a one-time dose that takes two to three hours to administer and protects against seven types of botulinum toxin.”  ^[17] Crane, Misti and Holly Zachariah. Getting botulism antitoxin no easy task. Columbus, Ohio: The Columbus Dispatch. 23 April 2015.

What the anti-toxin does is stop the botulism toxin from causing any further damage. It’s up to your body to repair the damage already caused, and that takes time.

If someone contracts botulism, the illness caused by the toxin produced by the spores, treatment must be fast, to minimize damage caused, and to prevent the damage tipping over into lethality:

The decision to treat must always be based on clinical observation, case history and physical findings and must not be delayed for the results of laboratory tests. Because antitoxin is the only specific therapy for botulism and because it is most effective early in the course of the disease, early administration is essential…At the neuromuscular junction, the toxin blocks the release of acetylcholine, which inhibits neuronal transmission resulting in flaccid paralysis. The toxin is not dislodged by the administration of antitoxin; hence, recovery only occurs when new terminals grow from the affected nerve end plate, a process that may take weeks or months.”  ^[18]McLauchlin, Jim, et al. Food-borne botulism in the United Kingdom. London: Journal of Public Health. doi:10.1093/pubmed/fdl053. 17 August 2006. Page 2 – 3. Accessed March 2015 at https://jpubhealth.oxfordjournals.org/content/early/2006/08/17/pubmed.fdl053.full.pdf

Outside the body, the toxin can be destroyed by heat. You’ll see different heat recommendations:

The Food Safety Authority of Ireland says,

The botulinum toxin itself is inactivated (denatured) rapidly at temperatures greater than 80°C .”  ^[19] Foodbourne Botulism. Food Safety Authority of Ireland. Accessed March 2015. 

The World Health Organization says,

…the toxin produced by bacteria growing out of the spores under anaerobic conditions is destroyed by boiling (for example, at internal temperature >85°C for five minutes or longer).  ^[20] Botulism. World Health Organization Fact sheet N°270. August 2013. Accessed March 2015.

Note that though acidity prevents the spores from germinating and creating the toxin, that acidity won’t kill the toxin once it has formed. If a jar of water-bathed green beans has botulism, then draining the beans and immersing them in pure white vinegar would still leave them toxic. Ditto opening a strawberry preserve that has gone bad and adding vinegar to it: it won’t help. “…a low pH will not degrade any pre-formed toxin.”  ^[21] Botulism. World Health Organization Fact sheet N°270. August 2013. Accessed March 2015 at https://www.who.int/mediacentre/factsheets/fs270/en/

What do people get botulism from?

You wouldn’t know it from hearing the canning people talk, but food, and particularly home canned food, is now actually the lowest cause of botulism.

It’s true that in the past, when people preserved more and shopped less, it was higher up on the list of of items causing botulism, but things have changed, and now it’s dropped and other causes have risen to the top.

“In the past, botulism was linked primarily to home-canned foods. In recent decades, however, botulism illnesses have been linked to foods such as unrefrigerated homemade salsa, baked potatoes sealed in aluminum foil, honey (the primary cause of botulism in infants), garlic in oil, and traditionally prepared salted or fermented fish.”^[22]Clostridium botulinum. USDA Food Safety and Inspection Service. 7 August 2013. Accessed November 2019 at https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/foodborne-illness-and-disease/clostridium-botulinum/ct_index

65% of botulism cases are infant botulism, 20% are wound botulism, and only 15% of cases are foodborne.

In the United States, an average of 145 cases are reported each year. Of these, approximately 15% are foodborne, 65% are infant botulism, and 20% are wound. Adult intestinal colonization and iatrogenic botulism also occur, but rarely. Outbreaks of foodborne botulism involving two or more persons occur most years and are usually caused by home-canned foods.” ^[23]  How common is botulism? In: Botulism. April 2014. Accessed March 2015.

And that foodborne percentage includes commercially-processed food at stores, and restaurant food.

That doesn’t mean that we shouldn’t aim to get home canned food off the list entirely, because it is possible if USDA guidelines are followed. It’s just rather to put it in perspective intellectually.

Let’s put botulism risk in perspective

When it comes to planning public health, no risk is acceptable. But, compared to other risks we face in life that happen despite all planning, where does botulism rate?

Cruise ship deaths and food poisoning

10 people a year die in just plain, ordinary, routine accidents on cruise ships; 2,100 a year get food poisoning.  ^[24] Hill, Catey. Here are the odds your cruise vacation goes horribly wrong. 24 January 2015. MarketWatch. Accessed March 2015. 

Penis Fractures

3 penis fractures a year occur in one city alone in Brazil.  “Over a period of 13 years (January 2000 and March 2013) in Campinas, Brazil (a city of 3 million people), researchers found 44 cases of penis fracture. That’s about 3 a year, in one city alone.” ^[25] Leonardo O. Reis, et al. “Mechanisms Predisposing Penile Fracture and Long-Term Outcomes on Erectile and Voiding Functions,” Advances in Urology, vol. 2014, Article ID 768158, 4 pages, 2014. doi:10.1155/2014/768158. Accessed July 2015. Worldwide, it’s a problem just now coming out of the closet.

Gun-related deaths

There are over  30,000 gun-related deaths a year in America.  ^[26] https://www.gunpolicy.org/firearms/region/united-states. Accessed March 2015

Pit bulls

Pit bulls killed 284 people, and severely mauled tens of thousands of others, in the period from 2005 t0 2017, and the rate is increasing as more pit bulls are adopted out into homes. ^[27]McCarthy, Niall. America’s Most Dangerous Dog Breeds. Forbes Magazine. 13 September 2018. Accessed November 2018 at https://www.forbes.com/sites/niallmccarthy/2018/09/13/americas-most-dangerous-dog-breeds-infographic/

If you cover for botulism you are covered for everything

Perhaps one of the main reasons that home canning officials focus on botulism (aside from the obvious inherent seriousness of the matter) is simply a practical one: as extremely rare as it is, if you take all the proper safe canning steps to cover for botulism, you have covered for all other dangers as well. Meaning all the other nasties such as listeria, salmonella, etc, will have been killed off quite handily just as a by-product of dealing with any possible botulism spores.

The Ontario government says,

Applying adequate temperature and acidity to control and eliminate the germination of Clostridium botulinum spores is also sufficient to effectively control the growth of other pathogenic microorganisms of concern in the home canning process.”  ^[28] Ontario Agency for Health Protection and Promotion (Public Health Ontario). Home canning: literature review. Toronto, ON: Queen’s Printer for Ontario; 2014. ISBN 978-1-4606-4166-8 [PDF] page 10 https://www.publichealthontario.ca/en/eRepository/Home_Canning_2014.pdf

How do they test that a home canning recipe will be safe from botulism?

The lab testers make the assumption that the jar will be colonized by 60 billion Clostridium botulinum spores:

And the underlying safety assumption is that when starting to sterilize a food product, there will be an impossible  60 billion C. botulinum spores present that need to be killed off…. There is generally considered to be an inherent safety factor in the assumption that there will be 60 billion resistant C. botulinum spores present. The application of such a large safety factor may compensate for an occasional can of food that heats more slowly than anticipated and for the occasional mechanical or human error that occurs in production.”  ^[29] N.M Anderson et al. Food Safety Objective Approach for Controlling Clostridium botulinum Growth and Toxin Production in Commercially Sterile Foods.  Journal of Food Protection, Vol. 74, No. 11, 2011, Pages 1956–1989 doi:10.4315/0362-028X.JFP-11-082.  Page 1960

For safety sake, they don’t actually work with Clostridium botulinum spores.

Instead, in the interests of biosafety, they use a similar bacteria named Clostridium sporogenes “PA 3679” as a surrogate that doesn’t produce a toxin.   ^[30] Harris, Linda J. and Sheryl Yamamoto. Master Food Preserver Slide Presentation. University of California Cooperative Extension. 9 October 2014. Accessed June 2015. Page 20.

…. considerable effort was made to find non-pathogenic organisms similar to C. botulinum in growth requirements and heat resistance which would readily produce spores. A putrefactive anaerobe, designated as No. 3679, was isolated from spoiled canned corn in 1927 by Cameron at the National Canners’ Association laboratory (Townsend et al, 1938). The resistance of this organism was in excess of the maximum recorded for C. botulinum, met other requirements, and is the major reference organism in use today”  ^[31] Andress, Elizabeth L and Gerald Kuhn. II. Early History of USDA Home Canning Recommendations. In: Critical Review of Home Preservation Literature and Current Research. Athens, GA: University of Georgia, Cooperative Extension Service. 1983. 

Note that another advantage to the surrogate that is used is that even higher temperatures are required to kill it off than botulism spores. That means yet one more margin of safety.

Geographic prevalence of botulism cases from improper home canning

Note that home canning is usually just linked in with any kind of food prepared at home as “home-processed” foods, so stats from poorly handled baked potatoes and chili boost up the “home food” numbers as well.

And, even when “food preservation” is singled out, canning isn’t the only form of food preservation, and it isn’t the only one where botulism can develop: also at documented risk are smoked fish, sausage, garlic stored in oil, roasted peppers in sealed plastic bags, etc.  ^[32] Kendall, Pat. Botulism. Document 9.305. Colorado State Extension.  May 2012. Accessed March 2015.

 America

There were 121 reported cases of botulism in 2009, of which 11 were foodborne, 84 infant, 23 wound, and 3 of unknown or other etiology (CDC 2014). In 2011, a total of 140 confirmed cases of botulism were reported to the CDC. Of these, 20 were foodborne, 102 infant, 13 wound, and 5 of unknown or other etiology (CDC 2014). ”  ^[33] Schneider, Keith R. Preventing Foodborne Illness: Clostridium botulinum. University of Florida IFAS Extension. Publication #FSHN0406. Revised December 2014. Accessed March 2015.

Again, note that foodborne does not necessarily mean home canned food.

Botulism is an expensive illness for American taxpayers: “It’s estimated that each botulism case costs the taxpayer over $725,000 US (2014 figures) by the time the last of the paperwork is done on it.”  ^[34] Andress, Elizabeth L. Research and Education in Food Preservation. Powerpoint presentation. 19 October 2014 at Food & Nutrition Conference & Expo, Atlanta, Georgia. Slide 7.

See dedicated page: Botulism from home canning in the United States

Australia

“There have been only six cases of botulism reported in Australia between 1991 and 2003.”  ^[35] Government of Victoria. Accessed March 2015 at http://ideas.health.vic.gov.au/bluebook/botulism.asp“

In 1991 … a couple became ill from consuming home-preserved unacidified asparagus. In Australia between 1942 and 1984 there were 5 outbreaks of botulism, affecting 53 people with 9 fatalities. Foods implicated include canned vegetables (mushrooms and asparagus) and canned tuna.”  ^[36] Clostridium botulinum. Meat & Livestock Australia. Accessed March 2015 at https://www.mla.com.au/off-farm/Food-safety/Food-safety-for-consumers/The-bug-bible/Clostridium-botulinum.

Canada

See: Botulism cases in Canada from unsafe home canning

New Zealand

Botulism incidences are not really singled out for tracking.

“There are no known New Zealand surveys of C. botulinum in foods.”  ^[37] NZFSA. CLOSTRIDIUM BOTULINUM. July 2010. Page 4. Accessed March 2015 at https://www.foodsafety.govt.nz/elibrary/industry/Clostridium_Botulinum-Neurotoxins_Produced.pdf.

Consequently as of 2010, there were only two cases that had been documented: “Only two confirmed intoxication cases (Type A) are known to have occurred in New Zealand. These were associated with home-preserved tiroi (watercress and boiled mussels) (Flacks, 1985). Boiling the mussels rather than steaming may have destroyed fermentation organisms, thereby reducing lactic acid production… ” ^[38] NZFSA. CLOSTRIDIUM BOTULINUM.

Botulism in the UK

Sickness and illness outbreaks related to home food preservation are not tracked and documented in the UK as they are officially and specifically tracked in North America. In the UK, food-related sickness and illness outbreaks are only tracked for commercially canned foods. Consequently a lot of data in the UK is just not available.

Cases of botulism in the UK are rare and home-canning is also quite an uncommon practice in the UK.”  ^[39] Kirsten Stone, Microbiological Food Safety Branch, Food Safety: Hygiene & Microbiology Division, UK Food Standards Agency to Lisa Rayner. Email. Quoted in: Rayner, Lisa. The Natural Canning Resource Book. The Natural Canning Resource Book. Flagstaff, Arizona: Lifeweaver LLC. 2010. Page 64.

But, cases do occur:

 The next incident of food-borne botulism occurred in 1998. A husband and wife of Italian origins brought back to England from Italy and consumed home-preserved mushrooms in oil. Both family members developed botulism (one died), and C. botulinum type B and BoNTB were detected in serum and faeces of one patient as well as in the bottled mushrooms. The bacterium alone was recovered from the faeces of the patient who died…. The remaining four incidents [Ed: of botulism in the UK] were associated with products from southern or eastern Europe which have previously reported much higher rates of food-borne botulism. The increased reporting of this disease is due to considerably more common practices of home or small-scale preservation where safe food preservation is inherently less under control than good commercial manufacturing processes…. The six incidents of food-borne botulism in the United Kingdom since 1989 illustrate the importance of recognizing the risk factors of poor processing or storage of commercially prepared foods, improper home preservation of foods.” ^[40] McLauchlin, Jim, et al. Food-borne botulism in the United Kingdom. London: Journal of Public Health. doi:10.1093/pubmed/fdl053. 17 August 2006. Pages 4,5. Accessed March 2015.

According to Moira Brett of the PHLS Central Public Health Laboratory in London, “There may be several reasons for the low prevalence of botulism in the UK. Perhaps the most important is that home preservation of non-acid foods such as meat, fish, and vegetables by methods other than freezing is actively discouraged and is now rare. Indeed, before an outbreak in 1998 caused by home bottled mushrooms produced in Italy, the previous outbreak known to be caused by home preserved food was in 1949.”  ^[41] Brett M. Botulism in the United Kingdom. Euro Surveill. 1999;4(1):pii=45. Accessed July 2015

One fisheries researcher has identified particular possible vulnerability from fish caught in inland waterways.  “Smoked salmon and hot-smoked trout and mackerel are the [fisheries] products most likely to give trouble in the UK.”  ^[42] Cann, D.C. Botulism and Fishery Products. Torry Research Station. Ministry of Agriculture, Fisheries and Food. Advisory Note No. 22. 2001. Accessed July 2015

Europe

The following cases are from a 2014 literature review conducted by a health authority in Canada. This is not meant to be a comprehensive list.

It should be sufficient though to address those in Europe who ask, does it ever happen here?

(Note: An instance from Thailand, and Argentina, were included in the findings.)

Reference	Year of Event	Location	Number of cases*	Most Likely Source(s)	Contributing Risk Factor(s)
Lonati D. et al. 2011 29	2011****	Italy	1	Home-canned homogenized turkey meal	Inadequate temperature treatment
Ağaçayak A. 2011 30	2011****	Turkey	4	Home-canned red peppers	Not reported
Oriot C., et al. 2011 28	2010	Corsica	5	Home-canned green beans and/or salted roast pork	Inadequate temperature treatment
Swaan CM., 2010 26	2008	Netherlands/ Turkey	8	Home-packed black olives	Inadequate pH of the final product
CDC, 200624 & Ungchusak K. et al. 2007 25	2006	Thailand	163	Home-canned bamboo shoots	Inadequate temperature treatment
Peck MW., 2006 9	2005	Russia	16	Home-canned cucumbers	Not recorded
Peck MW., 2006 9	2005	Kyrgyzstan	6	Home-canned salad	Not recorded
Peck MW., 2006 9	2005	Russia	5	Unspecified home-canned food	Not recorded
Peck MW., 2006 9	2005	Russia	15	Unspecified home-canned food	Not recorded
Mclauchlin J. et al. 2006**21	2005	United Kingdom	1	Imported home-preserved pork (from Poland)	Inadequate temperature treatment
Cengiz M., 2006 22	2005	Turkey	5	Roasted home-canned mushrooms	Not recorded
Pavlova V. et al. 2007 23	2005	Bulgaria	3	Home-canned pork	Not reported
Cengiz N., et al. 2004 19	2004****	Turkey	1	Home-canned green beans	Not recorded
Rebagliati V. et al. 2009** 10	1992-2004	Argentina	41	Improperly processed meats and vegetables and home-canned food: onions, pickled octopus, asparagus, fish and sweet corn.	Storing food under conditions that benefits the toxin’s growth
Varma KJ., 2004 **18	1980-2002	Georgia	565	Home preserved vegetables (implicated food for 80% of botulism cases)	Inadequate sterilization equipment and temperature treatment, canned food stored for too long and preserved vegetables eaten uncooked.
Cawthorne A. et al. 2005 20	2004	Italy	28	Restaurant-preserved green olives in saline	Inadequate pH of the final product
Peck MW., 2006 9	2004	Kyrgyzstan	5	Home-canned aubergine	Not recorded
Abgueguen P., 2003 15	2000	France	9	Home-canned asparagus	Not recorded
Mclauchlin J. et al. 2006**21	1998	United Kingdom	2	Imported home-canned mushrooms in oil (from Italy)	Not recorded

**Meta analysis studies, the number of case reported are sum of reported cases.

**** Year of publication was used when there was no information on the year the cases were reported.

Source:  Parto, Naghmeh. Ontario Agency for Health Protection and Promotion (Public Health Ontario). Home canning: literature review. Toronto, ON, Canada: Queen’s Printer for Ontario; 2014. ISBN 978-1-4606-4166-8 [PDF]  page 9.

See original document for footnoted sources within the table.

Poland

Botulism is the name given to the paralytic disease caused by the neurotoxin released by Clostridium botulinum. It is very rare in the UK, only 58 cases having been reported between 1922 and 1998. In Poland, however, several hundred cases are seen every year, attributable to the widespread practice of preserving foods in the home.”  ^[43] Biggs, M J P, and C A Quick. “Mysterious Dysphagia.” Journal of the Royal Society of Medicine 96.11 (2003): 549–550. Accessed March 2015.

Poland has historically reported high rates of botulism, e.g. during 1961 and 1998, between 81 and 738 cases per year were reported.  ^[44] McLauchlin, Jim, et al. Food-borne botulism in the United Kingdom. London: Journal of Public Health. doi:10.1093/pubmed/fdl053. 17 August 2006. Page 5. Accessed March 2015. 

Italy

The Italian habit of preserving vegetables in oil, and waving off suggestions that it could be unsafe as absurd, appears to be quite unsafe after all, causing around 40 cases of botulism a year.

Vegetables in oil have contributed to 54% of the cases of botulism in Italy between 1992 and 1996, where approximately 40 cases per annum have been reported (Aureli et al. 1999; Squarcione et al. 1999). Other vegetable preserves have been implicated in 10% of cases. While many of the products implicated were home-prepared, a proportion was produced commercially.” ^[45]Barbara M. Lund and Michael W. Peck. EVALUATION OF THE RISK OF GROWTH AND TOXIN PRODUCTION BY CLOSTRIDIUM BOTULINUM IN SELECTED NEW PRODUCTS OF CONCERN. Food Safety Science Division, Institute of Food Research, Norwich Research Park, Colney, Norwich. 2000. Page 21.

Geographic prevalence of Clostridium botulinum bacteria

Geographically, where is the bacteria actually found?

“C. botulinum is prevalent in soil and marine sediments worldwide, most commonly as spores. These spores are found everywhere.”  ^[46] USDA FSIS. Clostridium botulinum. August 2013. Accessed July 2015 at https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/foodborne-illness-and-disease/clostridium-botulinum/ct_index#3. 

Pat Kendall, USDA Extension Agent in Colorado says,

Colorado and other states in the West have higher per capita rates of foodborne botulism than other parts of the United States. One contributing factor is that the soil in the western U.S. from the Rocky Mountains to the Pacific Ocean contains a particularly high count of Type A Clostridium botulinum spores, the type of spores that produce the toxin most dangerous to humans.”  ^[47] Kendall, Pat. Botulism. Colorado State University Extension. Food and Nutrition Series|Food Safety. Fact Sheet No. 9.305. May 2012.

Different types of C. botulinum tend to proliferate in different places:

Botulinum spores are widely distributed in soils. Type A predominates in the western states and in New England; type B, in the eastern and southern states. Type E is usually associated with marine or fresh water environments throughout the world and is psychrotropic (Riemann, 1973). Type F has been isolated too rarely to establish its distribution pattern (Eklund et.al., 1967).”  ^[48] Food Technology & Processing. Introduction to the Microbiology of Food: The Microorganisms. Accessed March 2015 at 

In New Zealand, sediment has been identified as a particularly high risk context:

In New Zealand, Fletcher et al., (2008) collected 501 harbour and inshore coastal marine sediments. ….However the molecular method (PCR) detected Type A BoNT-producing genes in one sample… A previous New Zealand environmental survey based on sediments from lakes, oxidation ponds and tidal waters around Auckland, detected C- and D-producing strains at samples from 11/20 sites (Gill and Penney, 1982). Two reasons have been proposed for the apparent lack of Type E-producing strains in the New Zealand marine environment: geographical isolation and the consistently high salinity of New Zealand waters (>3%), which may prevent the organism from establishing…..  ^[49] NZFSA. CLOSTRIDIUM BOTULINUM. Page 4. 

Even if you are in a region where botulism hasn’t historically been in high concentrations in the soil…. the days are gone when your carrots come from down the road. Now, food travels and criss-crosses the globe:

An argument that is sometimes used against the recommendation that all low-acid foods be processed in a pressure canner is that C. botulinum rarely if ever is reported in the soil of some areas. However, considering the possible danger when contaminated food has not been adquately processed, the wisdom of recommending a canning process inadequate to destroy any pathogens that may be present is debatable. It is possible that vegetables shipped from another area may be canned. This reasoning is the basis for the recommendation that the pressure canner always be used for low-acid foods.”  ^[50] Penfield, Marjorie P. and Ada Marie Campbell. Experimental Food Science. San Diego, California: Academic Press. 1990. Page 272.

Pressure canning is the answer for low-acid foods

Failing to use a pressure canner for low acid foods is the botulism canning mistake.”  ^[51] Plemmons, Skip (2014-09-14). Next Generation Home Canning: Contemporary and Fun Recipes for Beginners. Kindle Edition.

….inadequate processing is the cause named in virtually every case investigated by public-health teams. The spores of C. botulinum—and it’s the spores that make the toxin, remember—can survive 5 hours or more of boiling at 212 F/100 C, even though the vegetative form of the bacterium is much more fragile. Therefore anything less than adequate Pressure-processing is a monstrous gamble. People who count on getting away with processing natural vegetables in a Boiling–Water Bath are playing for stakes too high.”  ^[52] Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (p. 129-130). Penguin Publishing Group. Kindle Edition.

Water-bathing low-acid foods actually increases the risk of botulism

Boiling something long enough to kill just spoilage bacteria, or sealing it to deprive them of air, can actually be the most dangerous thing you can do. It’s spoilage bacteria that can alert you that a food has gone off and should not be consumed. If you boil something for 10 hours and seal it, all you have done is kill off your early warning system bacteria, and left for the still-alive botulism spores a competition-free playground in which to flourish, with nobody left in the jar to warn you there is a problem.

The FDA says,

Mild heat treatments (heat shocks) in combination with Reduced Oxygen Packaging may actually select for C. botulinum by killing off competitors.” ^[53]FDA Food Code 2009: Annex 6 – Food Processing Criteria. Accessed November 2016 at https://www.fda.gov/Food/GuidanceRegulation/RetailFoodProtection/FoodCode/ucm188201.htm.

Clemson Cooperative Extension says,

In addition, boiling waterbath canning processes kill the competitive “good” bacteria that help prevent the growth of C. botulinum.” ^[54]Clemson Cooperative Extension. Canning Controversies: No to Home Canning Dairy Products. Accessed November 2016.

The National Center explains,

…removal of oxygen from the surrounding environment does not eliminate the possibility for all bacterial growth; it just changes the nature of what is likely to occur. In fact, what is most likely to be eliminated is growth of spoilage bacteria. The bacteria that normally spoil the quality of food in noticeable ways (odor, color, sliminess, etc.) like to have oxygen in the environment. If able to multiply on foods, these spoilage bacteria can let you know if a food is going bad before it reaches the point it makes someone sick. In an almost oxygen-free environment like vacuum packaging produces, the spoilage bacteria do not multiply very fast so the loss of food quality is slowed down.

Some pathogenic (illness-causing) bacteria, however, like low-oxygen environments and reproduce well in vacuum-packaged foods. In fact, without competition from spoilage bacteria, some pathogens reproduce even more rapidly than in their presence. These bacteria often do not produce noticeable changes in the food, either. In the vacuum-packaged environment, food may become unsafe from pathogenic bacterial growth with no indicators to warn the consumer; the bacteria that would also normally be multiplying and spoil food in ways to make it unappealing (odor, sliminess, etc.) are not able to function without enough oxygen.

For example, C. botulinum (a very dangerous pathogen that causes the deadly botulism poisoning under certain conditions) grows at room temperature in low-acid moist foods if the package presents anaerobic (lacking in oxygen) conditions – if the bacteria are present, of course. Without the competition from spoilage bacteria, reproduction is even easier. Refrigeration at 38-40 degrees F becomes a critical step for storage of low-acid vacuum-packaged foods that aren’t otherwise stable (don’t keep) at room temperature (e.g., canned properly). The actual temperature of the refrigerator and the temperature at which it keeps the food are essential to maintain safety of this product. If the food were not packaged under vacuum, the oxygen in the environment would offer some protection against C. botulinum growth and toxin development in the package.” ^[55]Andress, Elizabeth L. Should I Vacuum Package Food at Home? University of Georgia. 1999. Accessed November 2016.

Acidity neutralizes C. botulinum spores, not kill them

C. botulinum spores, if present in an acid food, will remain viable for a considerable period of time. Odlaug and Pflug (46) have shown that C. botulinum spores stored in acid media (pH 4.2) survived up to 180 days with little or no decrease in numbers. It will be normal for a fraction of the C. botulinum spore population present on foods to survive the heat processes given to acid foods and remain viable during storage. Presence of viable C. botulinum spores in properly preserved acid foods does not constitute a public health hazard because of the inability of these spores to grow at a pH of < 4.6.” ^[56]Odlaug,T.E. and Pflug,I.J. Clostridium botulinum and acid foods. Journal of Food Protection 41, 566-573. 1978.

It’s because the spores may be “sleeping” in jars of high-acid food that you really want to heat-process those jars, to kill off any moulds that may lower the acidity and allow the spores to “wake.”

What else can inhibit the C. botulinum bacteria?

High acid foods, provided the jars are properly processed to ensure that the foods will stay high acid (invisible moulds can lower the acidity), will be safe:

[Marisa McClellan] explains that most jams, jellies, preserves and pickles are high-acid foods, which can be safely processed in a boiling water canner with no risk of botulism. “It is impossible for botulism to develop,” McClellan said. “I really stress it just isn’t going to happen.”  ^[57] Weigl, Andrea. Find answers to common questions about canning. Newsobserver.com 3 June 2014. Accessed March 2015.

Technically, there’s a broader range of options even, but these include many processes and additives not typically available to home canners:

Primary growth-limiting factors for C. botulinum include environmental temperature above 122°F (50°C) or below 50°F (10°C); high acidity (pH <4.6); low water activity (lack of available moisture); food preservatives such as nitrite, sorbic acid, phenolic antioxidants, polyphosphates, and ascorbates; a low redox potential (absence of oxygen); and competing microorganisms (CDC 1998). …. If canning meats at home, consider including food preservatives such as nitrites in the brine solution to reduce the growth of C. botulinum. ”  ^[58] Schneider, Keith R. Preventing Foodborne Illness: Clostridium botulinum. University of Florida IFAS Extension. Publication #FSHN0406. Revised December 2014. Accessed March 2015 at https://edis.ifas.ufl.edu/fs104

Some noted incidents in the past

1924, Albany, Orgeon. “A typical family gathering on Feb. 2 turned lethal for people who ate home-canned green beans at the home of Emelia and Reinholt Gerber on Baker Street near what is now the Pacific Boulevard overpass. Over the next eight days, 12 would die from botulism.” ^[59]Albany Democrat. 2 February 1924. Page 1. Accessed June 2020 at https://www.gazettetimes.com/news/local/focus/a-city-mourns/article_47a1a013-f6b5-5864-9c9b-800b488ca6d0.html

1931, North Dakota, Twelve Dine With Death In Grafton Farm Home (improperly home-canned peas) ^[60]Twelve dine with death in Grafton farm home. Walsh County Record. 5 February 1931. Page 1. Accessed June 2020 at https://www.nal.usda.gov/exhibits/ipd/canning/exhibits/show/results/item/140

New York, 1974. “Thirteen members of a Bronx family are hospitalized with food poisoning suspected as botulism after they ate homecanned foods prepared by another family member who died earlier this week.” ^[61]Botulism Suspected in Illness Of 13 Members of Bronx Family. New York Times. 28 December 1974. Page 27. Accessed June 2020 from https://www.nytimes.com/1974/12/28/archives/botulism-suspected-in-illness-of-13-members-of-bronx-family.html?ref=oembed

Vancouver, Canada, 1987. 11 people. Improper home canning technique applied to mushrooms bottled in a restaurant. ^[62] http://www.bccdc.ca/resource-gallery/Documents/Educational%20Materials/EH/FPS/Food/BotulismInBritishColumbia_TheRISKofHomeCannedProducts.pdf

Toronto, Canada, 1999, 6 people including parish priest. Improper home canning of tomatoes.  ^[63]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2094941/

Can your home canning be safe from botulism?

Your home canning will be 190% safe from the risk of botulism if you follow a tested recipe developed based on science.  There are safety margins built-in “up the whazoo.”

And, if you do, you won’t have to worry either about a host of other food nasties such as straph, e.coli, listeria, salmonella, etc. All the procedures to deal with the Big B word will blow those guys out of the water quite early in the game.

The key to safe canning is following professionally tested recipes, such as those from the National Center for Home Food Preservation and from authors you trust. ‘People are very afraid of preserving their own food,’ [Sherri Brooks ] Vinton says. ‘They don’t have to be. Just follow the recipe.’ ”  ^[64] Weigl, Andrea. Find answers to common questions about canning. Newsobserver.com 3 June 2014. Accessed March 2015.

Further Reading

Canning / Sterilization of meat products. In: Meat processing technology for small- to medium-scale producers. FA). Regional Office for Asia and the Pacific. 2010. ISBN: 978-974-7946-99-4.

N.M Anderson et al. Food Safety Objective Approach for Controlling Clostridium botulinum Growth and Toxin Production in Commercially Sterile Foods. Journal of Food Protection, Vol. 74, No. 11, 2011, Pages 1956–1989 doi:10.4315/0362-028X.JFP-11-082

US Botulism incidences table 2008 and 2012 (bottom of page.) Schneider, Keith R. Preventing Foodborne Illness: Clostridium botulinum. University of Florida IFAS Extension. Publication #FSHN0406. Revised December 2014.