Recently there have been several tragic deaths of young doctors in Wuhan from covid19, including the 29-year-old Dr. Xia Sisi, the 29-year-old Dr. Peng Yin Hua, the 42-year-old Dr. Huang Wenjun, and of course the 34-year-old Dr. Li Wenliang.
This is at some odds with general population data showing that deaths of covid19 tend to be highly concentrated in the elderly. It could be a statistical anomaly, but it does seem like death rates may be higher in young doctors than would be expected in the population.
As an explanation, many of the most upvoted comments on these posts suggest that their immune systems might be suppressed due to overwork, poor sleep, and stress. To me, this seems to be an extremely unlikely explanation for many reasons, including the fact that doctors don't seem to die at relatively higher rates of other infectious illnesses such as influenza.
However, some people have mentioned higher viral load as a possibility, which seemed more likely. I did some research and I found this 2005 study on the role of viral load in SARS (which is very similar to covid19): https://wwwnc.cdc.gov/eid/article/11/12/pdfs/04-0949.pdf
The study looked at an outbreak of SARS in a particular housing area in Hong Kong. They found that people who had closer contact with the index patient had a higher nasopharyngeal viral load on admission as measured by RT-PCR. Crucially, they also found that people in this area were also the most likely to die. Some quotes:
"The median nasopharyngeal viral load in E block patients (5.09 log10 copies/mL) was much higher than in non-E block patients (0 log10 copies/mL) on admission (p<0.001)… The overall case death rate among the 79 patients was 24.1%. The highest rate was in block E, which accounted for 79% of all deaths, while the death rate in patients living in E7 (the same block as the index patient) was 70% (7 patients). This rate is significantly higher than in other units (p = 0.001 by χ2 test). The index patient was one of the few patients from E7 who survived the disease."
"Severity of illness did not differ between block E patients and non-E block patients when they were first seen at the hospital, despite higher viral load in block E patients. However, the death rate was higher in block E. We have previously demonstrated that patients with high initial and peak viral loads in nasopharyngeal samples were more likely to show a less favorable disease course and lower survival rate (8,18). Patients living in E7 who had highest nasopharyngeal viral loads explains why their death rate was higher than for those living in other units. The dilution effect resulted in a decreased viral load as the disease spread to other units and in a lower death rate."
This data corroborates the viral load theory. It's not perfect evidence, but the theory also makes basic physiologic sense. A higher viral load on initial infection means that the virus will be able to do more damage and suppress the host's immune system further (lymphopenia) before the host can mount an immune response against the virus.
Hospital workers are likely to be exposed to especially high viral loads of covid19. People who are hospitalized with covid19 infections are likely to cough more and require close contact for procedures such as IV placement and intubation. It is hard to know for sure, but healthcare transmission risk may have been especially high in the early stages of the epidemic in Wuhan, when people were not as aware of the high mortality rates of this disease.
If viral load upon initial infection correlates with disease severity, this may also help to explain why some local clusters seem to have more severe disease, such as the family who all died of the disease. For some reason, people in these clusters may have been exposed to an especially high viral load. Ideally, we could measure the viral load of infected people with RT-PCR to test this, although it's hard enough to get basic yes/no tests for covid19 at this point.
The viral load theory is not rock solid. It may not explain a large percentage of the variance in disease severity – certainly age seems to be a larger factor. But to me, it is clearly the leading theory why a disproportionate number of young doctors without apparent pre-existing health problems have died of covid19 in Wuhan.
Healthcare workers putting themselves at risk to care for the sick during this pandemic are heroes. It is an urgent priority to have sufficient PPE available to our healthcare staff. We also need to have adequate space available to allow for the adequate distancing of staff and possibly infected patients. The viral load theory suggests that PPE and distancing are not only important for preventing healthcare workers from getting the illness but also decreasing the likelihood that they will die of the illness if they are infected.
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