Whether It’s Covid, Monkeypox Or A Zombie Apocalypse, Here’s How To Investigate A New Epidemic
whether it’s covid, monkeypox or a zombie apocalypse, here’s how

Whether It’s Covid, Monkeypox Or A Zombie Apocalypse, Here’s How To Investigate A New Epidemic

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Infectious disease expert Dr. Mark Kortepeter explains how scientists take the first step in identifying a new disease epidemic.


Epidemiologists around the country track disease activity at county, city, and state health departments and the CDC. Warning of a possible new epidemic/outbreak can come in through a phone call, an email, a news report or review of routine disease surveillance data. Anyone on the receiving end of the call can relate to the contrasting feelings of dread mixed with the excitement of dealing with something new. Such notifications frequently arrive on a Friday afternoon just before the close of business, which makes launching an investigation challenging, because it is harder to reach people who have already left work for the weekend.

Investigating an outbreak is an important skill that is learned over time through trial and error. The CDC has an apprenticeship program, the Epidemic Intelligence Service, to mint new “disease detectives,” who spend two years embedded in one of the CDC departments or in a state or territorial health department, or other public health location. One of the key skills they learn is outbreak investigation.

Like any investigation, it is important to prepare before launching, and then to follow a tested series of steps in order not to miss anything.

Step 1: Confirm an outbreak is actually occurring

When that call or email comes in, the first questions are always: “Is this a real problem?” and “Is it something I need to worry about?” The last thing anyone wants to do is waste time and treasure chasing down rumors or something that doesn’t matter. As a baseline, it is useful to review current known disease activity from surveillance reports, assuming we know what the disease is. Is the disease activity normal for the time of year and location? Does this appear to be unusual in terms of who the victims are, their numbers, and the illness description? Some quick phone calls can help sometimes, but other times require driving or flying to the location to make an on-the-ground assessment.

Step 2: Make a diagnosis

If we don’t know the cause yet, we may have to start with only a constellation of symptoms (a syndrome) in the disease victims. From there, we need to understand what diagnostic tests have already been done on the patients, interview patients and their care providers, and collect specimens, such as blood, urine, sputum, and feces, for laboratory testing to make a diagnosis.

Step 3: Develop a case definition

At the outset of an outbreak investigation, we need to wrap our arms around how large the outbreak is and who might be affected. We do that by establishing a case definition, which includes common features we see in the ill patients. In the case of monkeypox, it might include someone with a fever and a pustular rash, and possibly includes contact with a known person with monkeypox. For Covid, it might include a person with a fever, cough, and loss of smell or taste. Whatever we choose, the case definition should be broad enough so as not to miss possible cases, but narrow enough to avoid pointing us in the wrong direction.

Step 4: Count how many people are impacted

Armed with a case definition, an epidemiologist can now search for cases to determine the extent of the problem. This is the concept of “shoe leather” epidemiology – the notion that the epidemiologist wears holes in their shoes from all the walking they do going house-to-house investigating the outbreak. As we have seen with monkeypox, after an initial notification in early May, once word got out and we started counting cases, there has been an explosion of greater than 3,000 cases identified on six continents. The problem keeps growing. Since it is likely that some of the cases may have already occurred before the investigation found them, one other critical factor is how many NEW cases are occurring over time. This helps us to determine whether the problem is getting worse, stable, or getting better.

Step 5: Assess what’s known about the new cases

Just knowing the numbers isn’t useful – what we really need to determine is what activities, exposures, and risks the ill individuals have in common. This clues us into who is at risk, what to tell the public about how the disease is spreading, and what risks and activities to avoid. In the 2003 outbreak of monkeypox in the United States, cases were linked to exposure to prairie dogs that had been infected by exotic pets imported from Africa. The current outbreak appears to be totally different and is spreading person to person. Most of the reported cases are occurring in men who have sex with men, but the question remains – is spread occurring through body fluids (i.e. sex), direct contact with skin lesions, or close respiratory contact. These are important distinctions to make to determine how to stop spread. We have yet to learn this definitively from an investigation.

One way to narrow down what exposures are leading to spread is to conduct a case control study. We would interview a number of the infected about their activities and possible risk factors for the disease exposure and then ask the same questions to a group of controls who do not have the disease. We can compare their answers using statistics to come up with a list of possible risks.

Step 6: Develop a hypothesis about how it’s spreading and test it

The case control study will help us make a hypothesis on mechanisms of disease spread. We take that information and assess whether the hypothesis make sense based on what we are seeing in the outbreak. Where are the holes in our theory? Do some people (called outliers) not fit in with the pattern we expect?

Step 7: Implement control measures and evaluate them

If we are confident we know how something might be spreading, we want to stop the spread. This is where we need to notify the public and enlist their assistance by telling them what they need to avoid. Even without final conclusions, CDC has already posted photos of monkeypox on its website and made such recommendations.

If we are correct about the mode of spread for the disease, we can monitor the number of new cases. Are we seeing a decline? If not, why not? Are people not doing what we ask? What have we missed?

Step 8: Learn from the experience and perfect the response for the next time

When we finally have the outbreak under control, it is time to take a step back and assess what we did well and what can be fixed for the next round – and there will always be a next round. One key tenet is that even though some things might have worked for this outbreak, we need to be mindful not to fight the “last war.” The next outbreak will be different, and it will require a different approach. The approach used for Covid-19 will not work for monkeypox. Regardless, the basic framework and steps I have described for chasing down an outbreak remain the same.

A good epidemiologist knows that every situation is different, and needs to be approached with an open mind. Every approach requires adaptation in real time as things change and new information becomes available. It just comes with the territory, but that is one aspect that makes outbreak investigation exciting.

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