A Commoner’s Guide to Investigating Food-Related Poisoning
Another large food related incident in India and this time around it has taken the lives of 22 innocent children. We still are unclear about how the chemical ended up in the school lunch. However, Indians and the political parties that represent them are terribly upset and they are demanding safe food for children. What they may not know, or choose to ignore, is that several thousand others across the country are dying slowly, suffering from infections caused by bacteria, viruses and parasites. These are children, adults and the elderly who have neither access to safe food and water nor good medical care and they are dying from diseases that can easily be prevented. Well, let us deal with the prevention later.
There is not a single week when I don’t come across a large outbreak of food poisoning in India. Some happen after wedding parties, some after religious festivals and most of them in schools. Such news gets into the mainstream media because a large number of people in a small area get sick simultaneously. Obviously, it’s easy to find the likely source of such large outbreaks that occur during large events – people know that they have all shared a common meal and nothing else that would make them sick. However, the story doesn’t end here for the food safety folks. If you have to prevent illness from occurring in the future, you need to find the likely food source and know exactly what led to the illness. Was it a bacteria, a virus, a parasite or a chemical that caused the illness? How did the bacteria end up in the food, or why was it not killed by cooking? How did the chemical get mixed with the food? Was it an intentional contamination (as the Osho Commune has been known to have participated in), a case of sabotage?
An investigation is never complete unless we know all the answers. Such investigations don’t occur in India despite having a strong scientific and medical community, largely because of the disconnect between organizations involved in public health and medical care. None are trained to do epidemiological studies that can link a food to the illness and its cause. That’s why we see reports blaming a lizard, rat or a cockroach for incidents of food poisoning- these are organisms that are perfectly edible if cooked well.
Here are two recent cases of food poisoning outbreaks in India.
Case 1: In September 2011, more than 500 students reported ill with symptoms of food poisoning in IIT Bombay. Thirteen of them were hospitalized and others responded satisfactorily to outpatient treatment. No fatalities were reported. IIT-B authorities conducted an investigation of food consumed by the students and found that all the people who were ill shared a common meal (a Chinese dinner) at their mess. They tested the water and some food and found nothing. However, the contractor who was running the mess was blacklisted. The Maharashtra Food and Drug Authority apparently investigated the case thoroughly but found nothing except that the food facility was maintained poorly.
Case 2: On 16th July, 2013, 20 children, aged four to 12, died after consuming a lunch of rice, soybean and pulses in the eastern state of Bihar. The school, in the district of Chapra, provided free meals under the Mid-Day Meal Scheme. It is likely that a container used for pesticide was used for food storage and thus the food got contaminated with organophosphates.
I thought it would be interesting to get some discussion going on these two cases. Figuring out what happened doesn’t require you to understand complex concepts of epidemiology. A few answers could help a long way:
Case 1- IIT Bombay:
What caused the illness?
From what I could understand from the news articles, most of the affected patients suffered from symptoms of gastrointestinal illness such as vomiting, abdominal pain and diarrhea within a few hours after eating the suspected meal. But, clinical symptoms aren’t enough to confirm an illness as food poisoning. We need to identify the biological/chemical agent that caused the illness, and link that to the food source. In the case of pathogens, we need to know how the organism multiplied to levels that could cause such a large outbreak. Vomit and stool samples of affected people and leftover food may have to be tested for the presence of toxins and pathogens. However, if we lack the facilities to do this, we can use ‘epidemiological studies’ and a bit of ‘food investigation’ to figure out what could have happened.
Can’t we test the food and find out what caused the illness?
Most of the infections occur 1 to 3 days after the contaminated meal is consumed. In such cases, it is unlikely that we may find leftovers of the same meal that caused the illness. Testing of food that belongs to the same batch of production could be useful, but not the foods that were produced later. It’s not necessary that the bacteria that caused the illness be present in all the batches of food, and processes such as heating can have a large effect on the contamination level in the end product. For example, pathogens present in a particular batch of meat that was not cooked properly could cause a large outbreak. If on the next day, the meat is cooked properly, that batch of food may not have pathogens. Stool samples of the affected people should be tested and pathogens isolated. This pathogen has to be then linked to the food ( ideally, it should be isolated from the food ) to confirm the source. . Investigation of foodborne infections need advanced techniques, both for testing and epidemiology. Understanding the limitations is a key to investigating such cases. Bottom line is – don’t jump into conclusions (such as blaming the lizard).
However, toxins produced by bacteria and chemicals such as pesticides affect people quickly. Depending on the dosage, symptoms are normally seen within a couple of minutes or hours. Toxin are pushed out by the body and this is manifested in the form of severe vomiting. Note that chemicals in the environment (toxic fumes) can also cause the same symptoms. This warrants rapid action to find the food or environmental exposure that caused the illness. Epidemiological studies could be useful to find the source without the help of testing.
Look at what the campus doctor in IIT had to say:
“Confirmatory tests, she said, require that same bacteria should grow from the stool samples as well as food. But since the food samples were not available, these confirmatory tests couldn’t be done. Regarding prevention she warned that students should know their vaccination schedule and take them timely.”
She has already assumed that it is a case of infection and not a toxin induced illness. Even though the symptoms clearly indicate the likelihood of intoxication, she has assumed that it is a type of pathogen that could be prevented by vaccination.
How can we link the food to the illness?
“ IIT-B authorities conducted an investigation of food consumed by the students and found that all the people who were ill shared a common meal ( a Chinese dinner) at their mess. They tested the water and some food and found nothing.”
The simplest thing to do is to do a cohort study and they have done it. However, I am not sure whether that was done properly. What they may not have realized is that testing fried rice is tricky. Fried rice is essentially cooked twice – first the rice gets boiled, then it gets cooled down and then boiled again. If the rice is kept at warm temperature for a long time after the initial boiling, a type of bacteria called Bacillus cereus can grow and produce heat stable toxins that will not be destroyed in the second heating (frying) step. The reheating step eliminates all live bacteria leaving the toxins that can make people sick. Testing of that sample of rice will not show any bacteria because they are all dead. Bacterial toxins cannot be isolated from food that easily and this gives us only one option, epidemiological studies and in this case a cohort study can help.
In case 1, I would have interviewed the people who were staying in the same hostel, both the ones that were ill and those who were well. This can help us to find out whether all the ill people were exposed to something in particular, may be some food, water or a chemical used in the hostel or surrounding area. The study will tell us whether all those who were ‘well’ weren’t exposed to the things that the ones that were ‘ill’ were exposed to and thus help us to narrow down our search. Sounds simple enough?
So, if 500 were sick and all of them had eaten the fried rice that was on the counter, it is likely that the fried rice had made them sick. But what if there was something else on the counter that all of them had also eaten?
This is where the data from the people who were not ill are going to help you. The meal history of the ‘well’ people should reveal that they had not eaten the food (or water) that all the ill people had eaten. If there is a mismatch here, it is likely that we are not looking at a case of food poisoning here and look for possible environmental exposure, say common air supply.
What is this talk about food sampling and testing then?
As I had mentioned earlier, food testing has its limitations. However, if it is a chemical agent, it is likely to stay in the entire lot- that has been cooked and un cooked. Such tests have to complement other investigations such as the results of the epidemiological study, environmental health investigation etc.
Let’s now move to case number 2 which looks pretty straight forward. Bacterial toxins in food are rarely fatal with the exception of toxins produced by an anaerobic bacteria, Clostridium botulinum. C. botulinum causes botulism, and since they are anaerobic bacteria, they are commonly associated with foods that are stored in anaerobic condition such as canned and vacuum packed food. This doesn’t seem to be the case in Bihar. Rapid onset of illness indicates a common exposure either through air or through food and water. The symptoms and the fatality indicate acute exposure to a highly toxic chemical. It could be pesticides or any other highly toxic chemicals that could have been intentionally added to the food. Investigators have narrowed down the cause to the chemical, but they have no idea how it landed in the food. Reusing a container used for pesticide for storage of drinking water and food is a common practice in India. However, the kind of dosage that’s possible from such an exposure is likely to be low. Severe illness and high fatality rate indicates a large intake of chemical and further investigations have to be done to find out whether it was an accident or an intentional contamination.
Though the incident in Bihar could be linked to a toxic chemical, most other outbreaks that occur in India, especially the ones that occur in schools, are likely to be due to inappropriate handling and storage of cooked foods. If cooked food such as rice is kept at room temperature for a very long time ( 4 hours or more), bacteria can multiply and produce toxins that could make people ill. Contaminated water, vegetables etc can also cause outbreaks, but most often infections that could sometimes be life threatening for malnourished children. When such outbreaks occur, identification of the pathogen that caused the illness can help find the food source and the conditions that led to the outbreak.
I will talk about the common practices that lead to food poisoning and prevention in another article. For those of you who are interested to learn more, you can look at CDC’s guide to confirm the diagnosis of foodborne diseases and figure out how clinical symptoms and tests can be linked to the pathogen or toxin. This page will give you information about chemicals that cause illness.It’s worthwhile to note that confirmatory tests for most pathogens can be done in several laboratories across India with the existing facilities. However, the disconnect between organizations in charge of public health, epidemiology, food inspection and testing makes it difficult for us to complete any investigation credibly. If you are working in the public health sector, World Health Organization’s guidelines for investigating foodborne illness could be handy.
Be food safe…..