Association between household exposure and cycle threshold in COVID-19 infected health care workers

Ai Chien,Harry Lampiris,Kristopher Taylor,Sandeep Guntur,Sandra Domeracki,Chuanyi M Lu,Paul D Blanc

doi:10.1186/s12995-021-00321-3

Abstract

ObjectiveHousehold SARS-COV-2 contact constitutes a high-risk exposure for health care workers (HCWs). Cycle threshold (Ct) of reverse transcriptase–polymerase chain reaction testing provides an estimate of COVID-19 viral load, which can inform clinical and workplace management. We assessed whether Ct values differed between HCWs with COVID-19 with and without household exposure.MethodsWe analyzed HCW COVID-19 cases whose Ct data could be compared. We defined low Ct at a cut-point approximating a viral load of 4.6 × 106 copies per ml. Logistic regression tested the association of household exposure and symptoms at diagnosis with a low Ct value.ResultsOf 77 HCWs with COVID-19, 20 were household exposures cases and 34 were symptomatic at testing (7 were both household-exposed and symptomatic at testing). Among household exposures, 9 of 20 (45%) manifested lower Ct values compared to 14 of 57 (25%) for all others. In a bivariate model, household exposure was not statistically associated with lower Ct (Odds Ratio [OR] 1.20; 95% Confidence Interval [CI] 0.97–1.51). In multivariable modelling both household exposure (OR] 1.3; 95% CI 1.03–1.6) and symptoms at diagnosis (OR 1.4; 95% CI 1.15–1.7) were associated with a low Ct value.DiscussionHousehold exposure in HCWs with newly diagnosed COVID-19 was associated with lower Ct values, consistent with a higher viral load, supporting the hypothesis that contracting COVID-19 in that manner leads to a greater viral inoculum.

Highlights

Cycle threshold (Ct) of reverse transcriptase–polymerase chain reaction, the number of amplification cycles for the target gene to exceed threshold detection, can provide an estimate of SARS-COV-2 viral load and may be related to infectivity and disease severity [1]
This supports the hypothesis that contracting illness through household exposure represents a greater viral inoculum than other Health care work (HCW) with acute SARS-COV-2 infection but without this exposure scenario
This could be related to multiple potential factors

Summary

Introduction

Cycle threshold (Ct) of reverse transcriptase–polymerase chain reaction, the number of amplification cycles for the target gene to exceed threshold detection, can provide an estimate of SARS-COV-2 viral load and may be related to infectivity and disease severity [1]. Among health care workers (HCWs) with COVID-19, Ct data have been analyzed in light of return-to-work protocols in one study and used in analysis of work-absence risk in another [3, 4]. Household exposure to SARS-COV-2 has been associated with a higher secondary attack rate than other sources of exposure, including acquisition in health care settings [5, 6]. This presumably reflects a greater intensity of exposure to the virus in persons acquiring COVID-19. In a cohort of HCWs with acute SARSCOV-2COVID-19 infection and with well-characterized contact tracing, we assessed whether the Ct differed between those with illness likely contracted from a household member compared to all others

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Conclusion