A family cluster of Middle East Respiratory Syndrome Coronavirus infections related to a likely unrecognized asymptomatic or mild case

BACKGROUND: Ninety confirmed cases of Middle East Respiratory Syndrome Coronavirus (MERS-CoV) have been reported to the World Health Organization. We report the details of a second family cluster of MERS-CoV infections from Riyadh, Saudi Arabia. METHODS: We present the clinical, laboratory and epidemiological details of 3 patients from a family cluster of MERS-CoV infections. RESULTS: The first patient developed respiratory symptoms and fever 14 days after admission to hospital for an unrelated reason. He died 11 days later with multi-organ failure. Two of his brothers presented later to another hospital with respiratory symptoms and fever. MERS-CoV infection in the latter 2 patients was confirmed by reverse transcriptase polymerase chain reaction testing. All 3 patients had fever, cough, shortness of breath, bilateral infiltrates on chest x-ray, thrombocytopenia, lymphopenia and rises in serum creatinine kinase and alanine transaminase. No hospital or other social contacts are known to have acquired the infection. It appears that the index patient in this cluster acquired MERS-CoV infection whilst in hospital from an unrecognized mild or asymptomatic case. CONCLUSION: MERS-CoV acquisition from unrecognized mild or asymptomatic cases may be a more important contributor to ongoing transmission than previously appreciated.