Ct Values do not Predict SARS-CoV-2 Transmissibility in College Students

SARS-CoV-2 is highly contagious, and the global spread has caused significant medical/socioeconomic impacts. Other than vaccination, effective public health measures, including contact tracing, isolation and quarantine, is critical for deterring viral transmission, preventing infection progression and resuming normal activities. Viral transmission is affected by many factors but the viral load and vitality could be among the most important ones. Although in vitro studies have indicated that the amount of virus isolated from infected people affects the successful rate of virus isolation, whether the viral load carried at the individual level would determine the transmissibility was unknown. From the diagnostic point of view, we aimed to examine whether the Ct value, a measurement of viral load by RT-PCR assay, could differentiate the spreaders from the non-spreaders in a population of college students. Our results indicate that while at the population level the Ct value is lower, suggesting a higher viral load, in the symptomatic spreaders than that in the asymptomatic non-spreaders, there is significant overlap in the Ct values between the two groups. Thus Ct value, or the viral load, at the individual level could not predict the transmissibility. Our studies also suggest that a sensitive method to detect the presence of virus is needed to identify asymptomatic persons who may carry a low viral load but can still be infectious.