Middle East respiratory syndrome coronavirus intermittent positive cases: Implications for infection control

BACKGROUND: Middle East respiratory syndrome coronavirus (MERS-CoV) continues to be reported from the Kingdom of Saudi Arabia. Data on the phenomenon of intermittent positive results for MERS-CoV on reverse-transcription polymerase chain reaction (RT-PCR) with negative results in between are lacking. Here we describe cases with intermittent positive MERS-CoV test results and highlight the required number of tests to rule out or rule in MERS-CoV infection based on a large retrospective cohort of patients with confirmed MERS-CoV. METHODS: This analysis included cases admitted between January 2014 and December 2017. The included patients had a minimum of 3 nasopharyngeal MERS-CoV RT-PCR tests for confirmation and needed 2 negative samples for MERS-CoV evaluated 48 hours apart with clinical improvement or stabilization apart to ensure clearance. RESULTS: A total of 408 patients with positive MERS-CoV test results were treated at the referring hospital. We excluded 72 patients who had only 1 swab result available in the system and were treated in the initial years of the disease. Of the remaining 336 patients, 300 (89%) had a positive result after 1 swab, 324 (96.5%) had a positive result after 2 consecutive swabs, and 328 (97.6%) had a positive result after 3 consecutive swabs. Of the total cases, 46 (13.7%) had a positive MERS-CoV test then a negative test, followed by positive test results. CONCLUSIONS: Our data indicate that 2 to 3 nasopharyngeal samples are needed to produce the highest yield of positive results for MERS-CoV. In addition, 2 negative results 48 hours apart with clinical improvement or stabilization are needed to clear patients from MERS-CoV. Evaluation of the yield of sputum samples is needed to assess the effectiveness against nasopharyngeal swabs.