The value of anal swab RT-PCR for COVID-19 diagnosis in adult Indonesian patients

OBJECTIVE: This study will test the performance of the anal swab PCR test when compared with the nasopharyngeal swab PCR test as a diagnostic tool for COVID-19. DESIGN: An observational descriptive study which included hospitalised suspected, or probable cases of hopitalised COVID-19 patients, conducted in Dr. Cipto Mangunkusumo National Hospital, Ciputra Hospital, Mitra Keluarga Depok Hospital and Mitra Keluarga Kelapa Gading Hospital, Indonesia. Epidemiological, clinical, laboratory and radiology data were obtained. Nasopharyngeal and anal swabs specimens were collected for SARS-CoV-2 RNA detection. RESULTS: We analysed 136 subjects as part of this study. The clinical spectrum of COVID-19 manifesation in this study was typical of hospitalised patients, with 25% classified as mild cases, 14.7% in severe condition and 12.5% of subjects classified as having acute respiratory distress syndrome. When compared with nasopharyngeal swab as the standard specimen for reverse transcription polymerase chain reaction (RT-PCR) detection of SARS-CoV-2 antigen, the sensitivity and specificity of the anal swab was 36.7% and 93.8%, respectively. The positive and negative predictive value were 97.8% and 16.5 %, respectively. The performance of the anal swab remained similar when only the subgroup of patients with gastrointestinal symptoms (n=92, 67.6%) was analysed (sensitivity 40% and specificity 91.7%). Out of all the subjects included in analysis, 67.6% had gastrointestinal symptoms. Similarly, 73.3% of patients in the anal swab-positive group had gastrointestinal symptoms. The two most common gastrointestinal symptoms in the subjects’ population were nausea and anorexia. CONCLUSION: Anal swab specimen has low sensitivity (36.7%) but high specificity (93.8%) for detecting SARS-CoV-2 antigen by RT-PCR. Only one additional positive result was found by anal swab among the nasopharyngeal swab-negative group. Anal swab may not be needed as an additional test at the beginning of a patient’s diagnostic investigation and nasopharyngeal swab RT-PCR remains as the standard diagnostic test for COVID-19.