Coronavirus incubation period may be longer than previously thought

A detailed clinical description of two cases of Middle East Respiratory Syndrome coronavirus (MERS-CoV) in France, published online in The Lancet today, suggests that the incubation period for the virus may be longer than previously thought, and longer quarantine periods may be required to rule out infection among patient contacts.

MERS-CoV – a novel virus, similar to that which caused the SARS outbreak of 2002-03 – was first identified in two patients suffering from severe respiratory illness in September 2012.  As of 23 May, 2013, there have been 44 cases worldwide [1].  The majority of cases have been identified in Saudi Arabia, with a smaller number of cases appearing in other countries in the Middle East (Jordan, Qatar, Tunisia, and United Arab Emirates), as well as the UK and France. The European cases were linked to people who had been travelling in the Middle East.

The new study provides the first detailed clinical description of the two MERS-CoV cases identified in France, outlining the symptoms the patients experienced, how they were treated, and how the virus was detected.  The first patient described, who has since died, appears to have become infected with the virus while travelling in the Middle East, and the second patient seems to have caught the virus while sharing a hospital room with the first patient (before doctors had detected the MERS-CoV infection), although the exact method of transmission is unclear.

The virus’s incubation period in the second patient appears to have been nine to twelve days, somewhat longer than the one- to nine-day incubation period previously observed, a finding with important implications for the duration of the quarantine required to rule out infection among contacts. 

For both patients, the virus could only be detected in samples taken from the lower respiratory tract – nasopharyngeal samples taken from the upper respiratory tract were negative or inconclusive for both patients.  While preliminary results in this paper suggest that the virus might be present in blood, the authors suggest that until further results are available, sputum samples from the lower respiratory tract should be taken to test for MERS-CoV infection.  Moreover, before MERS-CoV infection can be ruled out, initial negative results should be confirmed by a further sample taken a few days later.

Source: The Lancet