The fact that the diagnosis for the index case-patient was made by PCR of a serum sample collected 10 days after symptom onset and tested several weeks later highlights the value of testing serum samples for MERS-CoV RNA. This finding also provides valuable information about viremia in MERS CoV–infected patients, contributing to our understanding of the natural history of MERS-CoV infection and kinetics of virus shedding (7).
Given the incubation period of the disease (up to 15 days), the father most likely acquired his infection in Qatar (8,9). Patient 3, who had not traveled outside Tunisia, could have been exposed during the 11 days he cared for his father at home and in the hospital.
The history of patient 2 is less clear; she might have acquired the virus from the same source as her father in Qatar, or she might have been secondarily infected by contact with him before he left Qatar, given that her illness began almost 12 days after her father’s.
Patient 1 was severely ill at the time of ICU admission; in <3 days, his condition rapidly evolved to multiple organ system failure and death. Although we cannot account for the diabetes or corticosteroid contributions to his disease severity, we can speculate that they might have worsened his outcome. Other MERS CoV patients who have died had concurrent conditions (2), and corticosteroids are thought to worsen the outcomes for patients with influenza A(H1N1) virus infection (10).
The contact tracing results shed light on the potential for person-to-person transmissibility of MERS-CoV. Only 2 family members who had been in close and prolonged contact with the index case-patient became infected. Infection was not acquired by the case-patient’s wife, his 2 children who did not live with him, or the ICU workers who had short-term close contact with him.
However, these results should be interpreted cautiously because only nasopharyngeal swab samples obtained 5 weeks after contact with the index case-patient were tested. In addition, serologic testing, which was not performed in the present investigation, could have shed more light on person-to-person MERS-CoV transmissibility.