Sunday, 27 October 2013

MERS case-control study during the Hajj

Dr Ziad Memish, Deputy Minister of Health, Kingdom of Saudi Arabia, has made a welcome comment about some analysis of ill cases that went on during the Hajj. In the Saudi Gazette..

He added that in addition to detailed investigations of every suspected case, case-control studies for index cases and intensive follow-up of contacts with serological testing to improve understanding of the critical features of MERS-CoV infection were carried out.

I'm not clear on whether that indicates there were MERS-CoV cases during the Hajj, or if he is referring to probable cases that were not confirmed (no contacts then?) or to respiratory illnesses in general. He unfortunately wasn't quoted as saying whether any of those results were positive for MERS-CoV infection. 

Given that 997,3709 pilgrims apparently partook in some degree of medical healthcare service while in the KSA for Hajj, this study should provide some very useful information about what MERS-CoV was doing both in the ill and the healthy in mid-October. I might even be able to stop whingeing about lack of testing of all but those who are severely ill (or their contacts)!

The case-control study protocol is likely to follow that defined by the WHO in July - which can be found here.

The controls (best if >1 per case) will be randomly selected people of equal age (leeway varies with age band) and sex ("matched"), living in the same neighbourhood (to ensure try and capture the same environmental exposures; difficult for visiting pilgrims so general are of pilgrimage might suffice) that are not presenting with the same illness as the confirmed "case" at the time of sampling. Sampling (described in the lab testing WHO document here) which is recommended to include material from the lower respiratory tract - which may prove difficult from otherwise well controls. Informed consent is recommended as part of the (any such) study so controls will know what they are in for ahead do time.

Interestingly the WHO document comments that...

Currently, circulation of this virus in the community is thought to be nonexistent or minimal at most and the numbers of infections low. For that reason, prospective controls who have not had recent respiratory illness can be enrolled without laboratory

This study will address whether this is an accurate premise.