Symptoms predicting the onset and duration of SARS-CoV-2 infectiousness: A community cohort study

Objective To determine how upper respiratory tract (URT) viral load (VL) kinetics influence the timing, intensity, and duration of symptoms in SARS-CoV-2 community cases. Methods Our prospective community cohort provided daily URT swabs for VL quantification for 2 weeks and symptom diaries for 28 days post recruitment. Symptom data were summarized using a composite Symptom Burden Score (SBS) incorporating symptom presence and severity. Only cases who enrolled sufficiently early post exposure to discern peak (p)VL were included ( n = 89). Infectious viral shedding was assessed in a subset ( n = 37) through quantitative viral culture. Results The day of pVL correlated with the day of peak symptom burden score (pSBS) ( P < 0.001, n = 89). Very high pVL (>170,000,000 RNA copies/ml) was linked to prolonged illness, with a subset experiencing symptoms ≥3 weeks ( P < 0.001). Cases reported more symptoms, as well as an increase in URT symptom burden, on the first day of virus cultivability compared to the preceding day ( P < 0.001 and P = 0.005, n = 31). Peak systemic symptom score, and specifically muscle aches, significantly associated with prolonged infectious viral shedding ( P = 0.012 and P = 0.033, n = 34). URT symptoms such as rhinitis, sore throat, and hoarse voice showed the steepest increase at infectiousness onset. Conclusion The timing of pSBS aligns with pVL, and pVL above 170,000,000 RNA copies/ml predicts prolonged symptom duration. URT symptom escalation often marks the onset of infectiousness, while systemic symptoms, particularly muscle aches, signal prolonged infectiousness. These findings identify symptom-based markers of infectiousness with implications for testing strategies. They also highlight the importance of collecting early, frequent longitudinal symptom and virological data as a core element of the public health response to novel pathogens and future pandemics.