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

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.

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.

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.

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.