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. (C) 2018 Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved.