Performance & clinical utility of oropharyngeal versus nasopharyngeal swabs in COVID-19

BACKGROUND & OBJECTIVES: The oropharyngeal (OP) and nasopharyngeal (NP) swab samples are the most recommended clinical specimens for detecting SARS-CoV-2 in an individual through the quantitative real-time reverse-transcriptase-polymerase chain reaction (rRT-PCR) method. The primary objective of this study was to compare the performance of NP and OP swabs for the diagnosis of COVID-19 among 2250 concomitant samples (1125 NP + 1125 OP) using rRT-PCR test. METHODS: This study was conducted at a tertiary care hospital in southern India. The study compared the specificity and efficacy of the two samples (NP & OP swabs) in 1125 individuals suspected having COVID-19 infection. The rRT-PCR values from all the samples were compared based on gender, age group and viral load. The differences between unmatched proportion and matched proportion were analysed. Agreement between the two methods was assessed using Kappa statistic. Absolute sensitivity, specificity, positive and negative predictive values (PPV and NPV) for OP and NP swabs were analysed. RESULTS: The study identified a fair degree of agreement between OP and NP swabs in diagnosis of COVID-19 (kappa = 0.275, P<0.001). There was also a fair degree of agreement between NP and OP swabs irrespective of gender, age or duration of symptoms. NP swabs had better sensitivity and NPV as compared to OP swabs, however, specificity and PPV were 100 per cent for both. INTERPRETATION & CONCLUSIONS: The present study showed that both OP and NP swabs had similar sensitivity and specificity for predicting the presence of SARS-CoV-2.