How does a disease investigation work?

Y’all have heard by now that there’s a potentially community-acquired case of SARS-CoV2 in California.

What does that mean and how does public health respond?

Community-acquired means the patient doesn’t have a history of travel or direct exposure to someone who traveled, that they know of. That is, they don’t have a spouse or family member who was in Wuhan recently, and most likely are not sure from whom they caught it.

This is epidemiology. We have two goals: limit the spread and determine from whence it came. (June edit: We often can’t determine the source in a respiratory outbreak, so we focus on limiting the spread.)

If you’ve paid attention to recent measles cases, you’ll be expecting a list of all places visited on particular dates. But you may not get that, at least not immediately.

First, there’s HIPAA. That’s the health care privacy act that prevents the release of the patient’s information. In a public health investigation some information CAN be shared when absolutely necessary. What is absolutely necessary will depend on the situation. This can be a challenge, as some people — the public, government officials, etc — *expect* access to all information. The public health professionals leading the investigation must determine what information is essential to protecting the public’s health and what’s not. And I speak from experience here, sometimes you must do battle with people a lot more powerful then yourself to protect patient information in an outbreak.

I’m not involved in the CA investigation at all, but having conducted other investigations including during the H1N1 pandemic where the first case was identified just outside San Antonio, I can describe what is likely happening.

First, the epidemiologists and their teams are taking all information on the patient’s whereabouts for the past two weeks (or more). They’re listing any known contacts. Then they are contacting each individual on those lists. They’re checking those contacts for symptoms. They’re asking a list of questions about the contacts’ movement and travel. They’re asking if anyone they were around has been symptomatic. They are likely asking them to remain at home. Quarantine is a legal term, but they would ask for a voluntary home “quarantine.”

And it’s not just one visit. Those contacts are being visited daily to check for symptoms. (June edit: they’re not visiting contacts, but locally, those contacts are being followed up via phone calls with contact tracers.)

Now the teams are going to the next circle of contacts — all the contacts of the first contacts, and repeating the same process. They’re also going to any of the public places the patient had been since they were symptomatic. Depending on when the symptoms started, they may go back farther to an asymptomatic phase.

Public Health officials will then decide if they should put out a notice about those public places specifically. That may come, but it’s not the first step. Due to how we think SARS-CoV2 is transmitted, a person needs to be in fairly close contact to become infected. It’s a respiratory virus but that doesn’t mean it’s airborne. It appears to be transmitted by droplets. Droplet transmission means that when a person coughs, the virus is in droplets that may enter another person’s nose, mouth, or land on their hands which then touch the eyes/nose/mouth. We don’t yet know how long the virus can live on surfaces, but it’s not like measles virus which lingers in the air for hours.

Say the person went to the grocery store and coughed into their elbow when in the milk aisle. The likelihood that someone in the produce aisle will become infected is pretty much nil. Now, fomites are a concern, so they’re not ignoring the potential exposure, it’s just lower on the list of likely exposures.

Why not just tell everyone who was at that store to identify themselves to be screened? Because people panic. The last thing the local health care systems need is a rush on hospitals and clinics because everyone who was in that store is worried. You’ll also get folks who were never in the store but walked by, or who were there hours later or the next day, fearing exposure.

If the Public Health Department was to put out a list of places immediately, before they’d have time to investigate all the known contacts and therefore likely, they’d quickly be overwhelmed and unable to do their jobs effectively. Then we’d have an even bigger crisis.

Then there’s the very real impact that stigma has on the patient and their family and friends. Information like zip codes (or streets) can lead to areas or groups of people becoming targets. Scared people don’t always act rationally. We already know this from discrimination against Asian restaurants, businesses, and groups since this epidemic started.

And then the police have to get involved to protect the first group. Again, this is another burden on the capacity of a community resource.

Identifying information probably will get out, because it usually does. A list of places will probably, eventually, be released when it’s necessary. As the public, we’re not owed such information.

It’s essential that the professionals involved in the investigation, who have the real-world practical experience in conducting disease investigations, have the time and resources to do their jobs. And really, they WILL tell us what we need to know WHEN we need to know it. But that requires public trust.

Dr. Rohr-Allegrini is an epidemiologist and tropical disease scientist currently working to prevent diseases through immunizations.

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