Lancet just published results of a national covid seroprevalence survey based on plasma collected from US dialysis patients as part of their routine treatment. As of July, 8 percent of samples tested positive for covid antibodies. Compared with residents of mostly white neighborhoods, those living in black neighborhoods had 4 times the seroprevalence rate, while those from Hispanic neighborhoods had 2.5 times the white rate. “When compared with other measures of SARS-CoV-2 spread, seroprevalence correlated best with deaths per 100 000 population.” Only 9 percent of those testing seropositive for antibodies had been diagnosed with covid.
These findings generally support my estimates. Using a 0.85% fatality ratio as a lagging indicator of infection rate, I’d estimate a 6.4 percent US seroprevalence at the end of July — lower than the Lancet study’s 8 percent. The discrepancy isn’t surprising: as the article acknowledges, “Risk factors for acquisition of SARS-CoV-2 and for severe COVID-19, including advanced age, non-white race, poverty, and diabetes, are the rule rather than the exception in the US dialysis population.” Recently I estimated that blacks and Hispanics were between 5 and 6 times as likely as whites to be infected. That’s higher than the Lancet discrepancy; however, their method relied not on individual patients’ race or ethnicity but on the demographics of their residential neighborhoods.
It’s disturbing but not surprising that such a small percentage of seropositive dialysis patients have been diagnosed with covid. Everyone on dialysis has kidney failure; most also have diabetes and hypertension — major risk factors for dying of covid. It’s likely that, for a significant proportion of this highly vulnerable subpopulation who die during the pandemic, covid would have been the immediate but unrecognized cause of death, resulting in a significant undercounting of covid mortality. Consider also that most seropositive dialysis patients would have continued receiving essential regular treatment without having been diagnosed, exposing workers and vulnerable fellow patients at dialysis centers to contagion, typically four hours per session three times a week.