Patients on dialysis showed fewer unknown COVID-19 infections vs general population
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A study of patients on hemodialysis in the United States revealed that although the actual infection rate was greater than reported COVID-19 cases, this patient population had fewer unknown infections than the general population.
Adam G. Walker, PhD, of DaVita Clinical Research in Minneapolis, and colleagues attribute this finding to the “tight surveillance” placed on patients by dialysis clinics.
“Following guidance from the Centers for Disease Control and Prevention, U.S. dialysis organizations have put into place robust entrance screening procedures, whereby all patients entering a clinic are asked about symptoms, high-risk contacts, or both; patients who screen positive then undergo testing for viral RNA,” the researchers wrote. “These procedures, as well as the high rate of interaction with the health care system (~13 clinic visits per month for dialysis treatments), may lead to a narrower gap between viral infections and reported cases among maintenance dialysis patients.”
To investigate, Walker and colleagues determined seroprevalence (testing for IgG antibodies for SARS-CoV-2) in 12,932 patients who received dialysis treatments at DaVita clinics across the United States. Researchers used serum samples that were collected for routine laboratory screenings.
They considered such factors as state, sex, age and race, and focused on the ratio of seropositivity to the known COVID-19 case rate.
Overall, 5.8% of samples were seropositive, leading researchers to determine the actual number of infections was 1.7 times greater than reported cases (the known COVID-19 case rate was 3.3% during the study period).
Although seroprevalence was similar between men and women, further findings indicated variations between state, age and race.
For instance, seroprevalence was 1% in Kentucky vs. 23.6% in New York, while samples from Black and Hispanic patients were 7.3% and 7.7% positive, respectively, compared with 2.8% of samples from white patients. Samples by age indicated a seropositivity of 6% to 6.5% for patients younger than 70 years vs. 3.9% for those 80 years or older, a finding which the researchers theorize is due to greater infection-related mortality for older patients.
“Direct comparison of seropositivity rates in our sample to the general population of states must be interpreted cautiously for [two] important reasons: 1) our seroprevalence data were from a later period in time and are subject to be higher as the epidemic progressed; 2) the high-risk nature of maintenance dialysis patients,” Walker and colleagues wrote. “However, for states where general population data have been reported, seroprevalence in the dialysis population was approximately [two to three] times that in the general population ... Notwithstanding the above limitations (which would tend to bias in a direction that exaggerates risk in the dialysis population), this difference in seroprevalence is substantively lower than the [five-fold] difference in reported case rates between maintenance dialysis patients and the general population.”
Perspective
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Alan S. Kliger, MD
Patients on dialysis are at high risk of acquiring COVID-19 and, if infected, may have a mortality rate of 20% or higher. The high frequency of asymptomatic infections makes COVID-19 diagnosis particularly challenging.
Early in the pandemic, dialysis organizations adopted stringent policies to limit viral spread, with entrance testing, universal masking, separating infected patients from others, hand hygiene and personal protection equipment. How successful were these efforts in reducing unknown infections and thereby reducing infection spread?
In this paper, Walker and colleagues examined a national cross-sectional, quasi-random study of serum samples for IgG antibody to the SARS CoV-2 spike and nucleocapsid proteins among 12,932 DaVita hemodialysis patients between May 27 and July 1, 2020.
They found an overall seropositive rate of 5.8%, with geographic variation between 1.6% and 23.6%. Another study (Anand et al, Lancet 2020;doi:10.1016/S0140-6736(20)32009-2) of seroprevalence in 28,503 hemodialysis patients found a seropositive rate of 8%.
Both studies found patients who were 80 years old and older had lower seroprevalence, and that white patients had significantly lower seroprevalence rates than did Black or Hispanic patients. In the DaVita sample, the overall rate of patients diagnosed with COVID-19 was 3.3%, making the seropositive rate 1.7 times the clinical diagnosis. Thus, approximately 56% of seropositive patients were identified clinically with COVID-19. The Anand study estimated for the U.S. population, 9.2% of seropositive patients were diagnosed.
The authors of the DaVita study conclude that these findings suggest a lower rate of unknown infections among dialysis patients compared to the general population. While the authors acknowledge several limitations to their study, they nonetheless stress that this finding appears to hold in several individual states, and they speculate that this favorable finding may be due to the tight surveillance for COVID-19 during this pandemic.
Hemodialysis facilities and transportation to them thrice weekly make this a risky location for vulnerable patients during a pandemic. These findings suggest that undiagnosed infections are less prevalent among patients on hemodialysis than in the general population, and it is likely that the strict infection identification and prevention procedures adopted in dialysis facilities have been successful.
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