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By: Drew Barkley

Before I began working on my MPH, I knew very little about how foodborne disease outbreaks (or any outbreaks for that matter) were investigated. I just assumed that health departments would compare lab test results from a large group of people that got sick and look for commonalities in the foods they consumed or activities in which they participated. However, during my MPH and through my work at CFI, I have gained a greater knowledge and appreciation for the work that goes into an outbreak investigation. As a result, I would like to share a brief overview of the “Anatomy of an Outbreak Investigation” so that you might better appreciate the work that goes into such an investigation.

Outbreak Investigations can be divided into 3 main phases: descriptive, analytical, and intervention. The descriptive phase is first and is focused on information and data gathering. The analytical phase follows and uses the data gathered during the descriptive phase to look for potential risk factors and areas for intervention. The final phase, intervention, uses the results of the analytical phase to make more targeted interventions to try to halt the outbreak and stop the spread. I will now dive in and provide a little more detail on what occurs during the 3 phases.

The first step of the descriptive phase (and of any outbreak investigation) is to determine if an outbreak is occurring.  Here, it is worth mentioning the definition of an outbreak. An outbreak or epidemic occurs when we see levels of a disease above what is expected. For example, we expect to have a certain number of flu cases each flu season. However, if we see higher levels of flu than expected (as with 2009-2010 H1N1), an outbreak is declared. In the case of the 2009-2010 H1N1 outbreak, because it was an epidemic or outbreak affecting the whole world, we refer to it as a pandemic. Right, so back to step 1. To understand an outbreak is occurring, we must know if the number of cases of a disease is higher than we expect. For foodborne disease, this is done through surveillance systems such as FoodNet and PulseNet. Each year, we expect a certain number of sporadic cases of the various foodborne pathogens (Salmonella, E. coli, Campylobacter, etc.) based on trends from previous years. If we ever see an unexpected spike in cases, the alarm is sounded, and an outbreak is declared. Outbreaks can also be declared when a specific strain of a pathogen is detected in several, seemingly unrelated people. This is done using PulseNet which sequences pathogens recovered from sick individuals. If the same sequence appears in multiple individuals, an outbreak can be declared.

The next step of the descriptive phase is to create a case definition and identify your outbreak cases. Setting an appropriate case definition is an important step as making the definition too inclusive may overload the system and overestimate the size of the outbreak. However, making the definition too exclusive will leave out cases and valuable data. Using simple, objective criteria for the case definition is the best way to ensure systematic and uniform inclusion of cases. The case definition can also evolve over time as more is learned about an outbreak. For example, if an outbreak of Salmonella were occurring, you might start with a case definition of any individual with lab-confirmed Salmonella matching the outbreak strain. Then as you learn risk-factors and potential source foods, you can target the case definition to be any individuals with lab-confirmed Salmonella matching the outbreak strain who ate certain foods or attended a specific event.

Once the cases are identified, you want to begin part 3 of the descriptive phase, describing the occurrence of disease in time and place. Here is where you will find the “epidemic curve,” a plot showing cases over time, as well as maps showing spatial trends in the outbreak. In a foodborne outbreak investigation, investigators will also conduct interviews with confirmed cases to obtain information on what they ate, how they prepared food, if they attended any events or restaurants, etc. These interviews are performed by local health departments and contain questions based on previous foodborne contamination events in order to avoid bias and better direct questions. The information gathered here will aid investigators in the analytical phase of the investigation.

Speaking of the analytical phase, that is the next stop in our outbreak investigation. This phase has two steps: hypothesis generation and hypothesis testing. Using the epidemiological data collected in phase 1, investigators try to answer the following questions:

  1. What is the cause of the outbreak? (what is the pathogen or infectious agent?)
  2. What is the source of the outbreak? (common point source or multiple sources?)
  3. How did the outbreak spread? (what is the transmission pathway?)
  4. What are the risk factors associated with the outbreak?

The goal behind answering these questions is to identify key components of the outbreak in order to inform the third and final phase of the outbreak investigation.

The last phase of an outbreak investigation is the intervention phase. Similar to the previous phase, there are 2 parts to the intervention phase: implementing control and prevention measures and communicating the findings. The goal of any outbreak investigation is to stop the outbreak from spreading and limit the number of illnesses and deaths. Information gathered during the previous two phases of the investigation informs the interventions of the third phase. For example, in foodborne disease outbreaks, once investigators learn the source of an outbreak (i.e. romaine lettuce from Yuma, AZ), they will advise people to avoid food from that source until corrective action is taken. In cases where there is a food processor or company behind the outbreak, investigators will gather enough information to convince the processor or company to make a voluntary recall in order to help prevent the spread.

Lastly, it is crucial to communicate the findings from any outbreak investigation. As humans, we can make mistakes while learning along the way. In an outbreak investigation, mistakes may get made and there may be things the investigators wished they had done differently. By communicating and reporting on the outbreak as it happened, future investigations can be aided by the knowledge gained during previous investigations. Once the final numbers are in and reported, the outbreak investigation can be closed. Hopefully now you have a better understanding of how outbreaks are investigated and the work that goes into completing such an investigation. If you would like to dive deeper into how outbreak investigations occur, I recommend starting at the CDC’s website at the following link: 

Drew BarkleyDrew Barkley

Graduate Research Associate




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Compost, Photo by Trevor Wade on

By: Allison Howell

In 2011, the FAO released a report with a startling statistic: nearly 1/3 of food produced in the world is wasted or lost. Since then, reducing food waste has become a hot topic 1.  One popular method of reducing the amount of food waste sent to landfills at the consumer level is composting. Composting is a process of converting organic waste, such as fruits, vegetables and yard waste like leaves and grass clippings into a mixture for promoting plant growth, a “natural” fertilizer. This fertilizer can then be used to provide fuel for your plants, vegetable gardens, or window boxes. While commercially produced and distributed compost is subject to regulation by the Ohio EPA, compost created at a home residence is not subject to regulation or inspection. Without any sort of regulation into the safety of home-generated compost, risk arises in using the compost for vegetable or herb gardens, where the plant grown is intended to be consumed.

Today, there are lots of options for individuals to start composting. A quick search for “home composting” reveals a plethora of articles and guides for individuals to start composting. Some require the use of compost bins which can cost anywhere from $60 to upwards of $200, but you can also find DIY guides that require only space, time, and lots of browns (carbon-rich materials like leaves, newspapers, and twigs) and greens ( nitrogen or protein rich materials like grass clippings, fruit and veggie scraps, or egg shells).2 The EPA provides guidance on which waste items can be composted at home and which should not. While most yard and food scraps can be composted, some should be avoided for food safety and feasibility reasons. Dairy and meat may be hosts for harmful bacteria like Salmonella or E. coli. Composting contaminated foods would lead to the spread of pathogens onto the crops that is fertilized. Moreover, composting these items can attract pests or insects to the compost, which could again lead to transmission of pathogens.

However, for those low on space or time, but rich in browns and greens, community composting groups have begun to pop up in some neighborhoods. The mechanics of composting are the same, but the logistics make composting much easier (and possibly less stinky) for consumers. Composting programs such as the Compost Exchange in Columbus, Ohio provide subscribers  with a plastic bucket and compostable liners to collect compostable materials and then collect the contents of the bucket to be composted at their own facility. Programs like this are becoming quite popular. A 2019 report from US Public Interest Research Group revealed that the number of communities offering composting programs like Columbus’ Compost Exchange has grown by 65 percent over the last five years3.

So what exactly happens to the compost generated by at-home composters or community composting groups?

  • If you compost at home, you can reap the benefits of your hard work and use the compost as you wish to fertilize plants. Most composting groups also make the final compost product available to those that helped contribute the browns and greens necessary, sometimes free and sometimes for a small fee.

The final piece of this composting puzzle is where the food safety questions begin to arise. Here are some common questions about composting and food safety.

  • Is it safe to use homemade compost as a fertilizer for home-grown fruits and vegetables?
    • Probably. If you composted the correct materials and incorporated an appropriate amount of air and water to your compost.
  • What if I accidentally composted something that I shouldn’t have? Can I still use my compost as fertilizer for plants that will be eaten?
    • It depends. There are various reasons why certain items should not be composted and the resulting risk of incorrectly composting an item may vary based on that reason. To be safe, it would be best to not use for growing food, though you could use it for flowers or decorative plants.
  • How do I know that my compost is ready to be used as fertilizer? If I use it before it’s ready, am I going to get sick?
    • Compost is ready to use after it no longer resembles the starting materials, but looks like potting soil. It should feel cool and crumbly when touched4. It’s unlikely that compost contains pathogenic bacteria that could make you sick, but it could happen. There is always chance food could make us sick, and it is possible that harmful bacteria may be present in a compost heap at some time or another.

The rise of composting as a mechanism for reducing food loss (see the important distinction between food loss and food waste here), is a great advancement towards creating a more sustainable food system. But this excitement must be balanced with a conservative approach to and consideration of how composting might affect the safety of food, which it is used to fertilize down the line.  To quote a 2018 review article on the topic “Understanding the mechanisms of pathogen survival during the composting process and mechanisms that reduce pathogen populations can minimize the risk of pathogen contamination in the cultivation of fruits and vegetables”5. An aptly-titled 2020 article from Food Safety News “Cook your compost to the same temperature as your burgers” provided several important calls to action for individuals looking to start composting. However, the first action item cited by Brian Bonner is to “educate yourself on composting’s benefits and risks” is perhaps the most important6. The act of composting is positioned uniquely between two major areas of food studies: food safety and food loss and waste. To make responsible decisions and minimize food safety risk while maximizing the benefit of reducing food waste and loss, education is an imperative first step. Learning about and incorporating an understanding of food safety risk in your approach to composting can help ensure that the compost generated by your efforts best nourishes plants without introducing additional food safety risks to the friends, family, or even strangers that may end up consuming compost-fertilized produce.

1. Food Loss and Food Waste. Food and Agriculture Organization of the United Nations 

2. Vanderlinden, C. Which Items Are ‘Greens’ and Which Are ‘Browns’ for Composting? The Spruce

3. Composting in America | U.S. PIRG.

4. Composting | NRCS.

5. Gurtler, J. B. et al. Composting To Inactivate Foodborne Pathogens for Crop Soil Application: A Review. J Food Prot 81, 1821–1837 (2018).

6. Bonner, Brian. Cook your compost to the same temperature as your burgers. Food Safety News

Allison HowellAllison Howell

Graduate Research Associate






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