COMMENTARY

Armchair epidemiology


 

Real epidemiologists are out knocking on doors, chasing down contacts, or hunched over their computers trying to make sense out of screens full of data and maps. A few are trying valiantly to talk some sense into our elected officials.

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This leaves the rest of us with time on our hands to fabricate our own less-than-scientific explanations for the behavior of the SARS-CoV-2 virus. So I have decided to put on hold my current mental challenge of choosing which pasta shape to pair with the sauce I’ve prepared from an online recipe. Here is my educated guess based on what I can glean from media sources that may have been filtered through a variety politically biased lenses. Remember, I did go to medical school; however, when I was in college the DNA helix was still just theoretical.

From those halcyon days of mid-February when our attention was focused on the Diamond Princess quarantined in Yokohama Harbor, it didn’t take a board-certified epidemiologist to suspect that the virus was spreading through the ventilating system in the ship’s tight quarters. Subsequent outbreaks on U.S. and French military ships suggests a similar explanation.

While still not proven, it sounds like SARS-CoV-2 jumped to humans from bats. It should not surprise us that having evolved in a dense population of mammals it would thrive in other high-density populations such as New York and nursing homes. Because we have lacked a robust testing capability, it has been less obvious until recently that, while it is easily transmitted, the virus has infected many who are asymptomatic (“Antibody surveys suggesting vast undercount of coronavirus infections may be unreliable,” Gretchen Vogel, Science, April 21, 2020). Subsequent surveys seem to confirm this higher level carrier state; it suggests that the virus is far less deadly than was previously suggested. However, it seems to be a crafty little bug attacking just about any organ system it lands on.

I don’t think any of us are surprised that the elderly population with weakened immune systems, particularly those in congregate housing, has been much more vulnerable. However, many of the deaths among younger apparently healthy people have defied explanation. The anecdotal observations that physicians, particularly those who practice in-your-face medicine (e.g., ophthalmologists and otolaryngologists) may be more vulnerable raises the issue of viral load. It may be that, although it can be extremely contagious, the virus is not terribly dangerous for most people until the inoculum dose of the virus reaches a certain level. To my knowledge this dose is unknown.

A published survey of more than 300 outbreaks from 120 Chinese cities also may support my suspicion that viral load is of critical importance. The researchers found that all the “identified outbreaks of three or more cases occurred in an indoor environment, which confirms that sharing indoor space is a major SARS-CoV-2 infection risk” (Huan Qian et al. “Indoor transmission of SARS-CoV-2,” MedRxiv. 2020 Apr 7. doi: 10.1101/2020.04.04.20053058). Again, this data shouldn’t surprise us when we look back at what little we know about the outbreaks in the confined spaces on cruise ships and in nursing homes.

Dr. William G. Wilkoff practiced primary care pediatrics in Brunswick, Maine, for nearly 40 years.

Dr. William G. Wilkoff

I’m not sure that we have any data that helps us determine whether wearing a mask in an outdoor space has any more than symbolic value when we are talking about this particular virus. We may read that the virus in a droplet can survive on the surface it lands on for 8 minutes, and we can see those slow motion videos of the impressive plume of snot spray released by a sneeze. It would seem obvious that even outside someone within 10 feet of the sneeze has a good chance of being infected. However, how much of a threat is the asymptomatic carrier who passes within three feet of you while you are out on lovely summer day stroll? This armchair epidemiologist suspects that, when we are talking about an outside space, the 6-foot guideline for small groups of a dozen or less is overly restrictive. But until we know, I’m staying put in my armchair ... outside on the porch overlooking Casco Bay.

Dr. Wilkoff practiced primary care pediatrics in Brunswick, Maine, for nearly 40 years. He has authored several books on behavioral pediatrics, including “How to Say No to Your Toddler.” He has no disclosures. Email him at [email protected].

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