Cycle threshold and viral load in SARS-CoV-2-infected patients in Sonora, Mexico

SARS-CoV-2 infection is confirmed with the polymerase chain reaction test. Its positivity is determined by the cycle threshold (Ct), which is inversely proportional to viral load.

To describe clinical and epidemiological characteristics of SARS-CoV-2-infected patients according to their viral load estimated by Ct.

Cross-sectional study that included 21,110 confirmed cases, which were stratified according to their viral load: low (Ct > 30), medium (Ct 25-30) and high (Ct < 25).

High viral load was identified in 53% of the cases, hospitalization was more common in subjects with medium viral load, and deaths were more prevalent in those with high viral load. Median Ct was lower during the first five days and linearly increased with the days of clinical evolution. There was a higher prevalence of deaths, hospitalizations and ventilatory support in subjects with confirmed SARS-CoV-2 infection who had a medium and high viral load.

The Ct value, correlated with other patient characteristics, can guide the prognosis, as well as the design of interventions that limit the spread of the virus within the population.