Upper Respiratory Tract COVID-19 Viral Load May Effectively Stratify Patients at High Risk for Severe Infection

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Viral load of the COVID-19 in the upper respiratory tract may be an effective stratification method for severe outcomes, length of stay, and death.

Viral load of the coronavirus disease 2019 (COVID-19) in the upper respiratory tract (URT) may be an effective stratification method for severe outcomes. These findings, from analysis of a national surveillance database in Greece, were published in the Journal of Infectious Diseases.

Patients (N=1122) who were diagnosed with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at 3 major reference laboratories in Greece were included in a database collected by the National Public Health Organization. RNA was extracted from nasopharyngeal or oropharyngeal swabs. Patients were stratified as having high (<25 Ct), moderate (25-30 Ct), or low (>30 Ct) viral loads. Severe COVID-19 infection was defined as admission to the intensive care unit (ICU), intubation, or death.

Patients were 55.2% men with an average age of 46 years, 29.9% of patients had at least 1 comorbidity. Of the 1122 patients diagnosed with COVID-19, 24.4% had an asymptomatic infection.

Patients with symptoms of COVID-19 were tested by swab an average 5.91±5.54 days after symptom onset. Among the patients with symptomatic infections (75.6%), 61.1% were hospitalized. Of the hospitalized patients, 19.1% were admitted to the ICU, 17.9% were intubated, and 17.2% died.

Patients’ URT viral load was categorized as either low (44.3%), moderate (28.2%), or high (27.5%). Stratified by viral load, those with high URT load were significantly older (P =.001) with higher rates of immunosuppression (P =.001), hypertension (P =.002), obesity (P =.005), chronic cardiovascular disease (P =.019), chronic pulmonary disease (P =.026), and chronic neurological disease (P =.026) comorbidities compared with moderate and low viral loads.

Patients with high URT viral load were less likely to be asymptomatic (13.6% vs 22.5% vs 32.4%; P <.001) and more likely to die (11.3% vs 7.3% vs 6.2%; P =.030) or be intubated (11.3% vs 8.2% vs 6.4%; P =.011) compared with intermediate or low viral load statuses, respectively.

Compared with low viral loads, patients with high URT load were intubated (P =.006) and remained in the ICU (P =.011) for longer periods of time.

Severe SARS-CoV-2 infection was increased among patients of increased age (odds ratio [OR], 1.03; 95% CI, 1.02-1.05; P <.001) with comorbidities (OR, 1.67; 95% CI, 1.15-2.42; P =.006) and was decreased among women (OR, 0.41; 95% CI, 0.25-0.65; P <.001).

This study may have been limited by pooling results from both nasopharyngeal and oropharyngeal swabs. It remains unclear whether URT viral load in the nasal or oral passageways are equivalent with regard to severe SARS-CoV-2 infection outcomes.

These data indicated patients with high URT viral load were more likely to present with COVID-19 symptoms, be intubated or remain in the ICU for longer periods of time, and have higher mortality risk. Quantification of viral load when assessing COVID-19 positivity may be an effective strategy for stratifying patients at risk for severe infection.


Maltezou HC Raftopoulos V, Vorou R, et al. Association between upper respiratory tract viral load, comorbidities, disease severity and outcome of patients with SARS-CoV-2 infection. J Infect Dis. Published online January 3, 2021. doi:10.1093/infdis/jiaa804.