Tuesday, June 21, 2016

Saudi MOH CCC: Asymptomatic MERS-CoV Infections


Over the past half year the Saudi MOH has done a much better job conveying information about their MERS response via a Weekly MERS Monitor report from their CCC (Command & Control Centre), which are published at this link.

This week, the focus is on asymptomatic cases and the current nosocomial outbreak in Riyadh.

Until about 10 months ago the Saudi MOH treated RT-PCR positive but asymptomatic cases as something less than a true MERS case, rarely isolated them, and inconsistently reporting  them to the WHO.

Like most viral infections, MERS-CoV can produce a wide range of symptoms, and so many mild or asymptomatic cases likely go undiagnosed. And for a large number of community acquired cases, the source of their infection remains a mystery.
Asymptomatic carriage and transmission offers one plausible, if not yet proven, explanation (see Study: Possible Transmission From Asymptomatic MERS-CoV Case).

All of which came to a head last September in the WHO Statement On The 10th Meeting Of the IHR Emergency Committee On MERS which contained unusually blunt criticisms of the Saudis for their handling of asymptomatic cases (among other issues). 

Last fall we began to see better handling and reporting on asymptomatic cases, and more openness on the part of the Saudi MOH.  

Which brings us to the CCC's weekly monitor report, which includes the following on asymptomatic cases and their handling.

Asymptomatic MERS Infections

Contact tracing during a recent outbreak of (7) cases of MERS in one of the major hospitals in Riyadh revealed
18 asymptomatic infections.

Editorial Notes

Since 2012, approximately 20% of laboratory confirmed MERS cases have been classified as asymptomatic or having mild disease at the time of testing. Serological tests revealed that RT-PCR could detect only 50% of asymptomatic infections. 

Sometimes it is difficult to classify a case as ‘asymptomatic’ because although the person may not have any symptoms at the time of testing, he or she may develop illness during the course of infection. Most MERS cases among children appear to be asymptomatic; severe disease can occur in children with underlying conditions. Asymptomatic infections could pose difficulties for control efforts if these individuals are able to transmit the virus to others.

Thus, when MERS cases are detected, one of the major interventions is to monitor contacts for symptoms of MERS. The potential for transmission of infection from asymptomatic RT-PCR positive persons is currently unknown.

The virus does not appear to pass easily from person to person unless there is close contact, such as providing unprotected care to an infected patient. However, prolonged nasal virus RNA detection (more than 5 weeks) from one asymptomatic RT-PCR positive Healthcare Worker (HCW) has been reported. A study found that about 2% of contacts were positive for MERS on PCR assays and the viral loads varied from below 500 copies to 80,000 copies. 

Mild symptoms occurred in one contact that developed  pharyngitis  and  the  highest   viral   load;   i.e.,   contagiousness does  not  completely  coincide  with symptoms.

According to MoH guidelines, asymptomatic RT-PCR positive persons; especially HCW, should be isolated, followed up daily for symptoms and tested at least weekly – or earlier, if symptoms develop – for MERS-CoV.
The decision on where to isolate asymptomatic RT-PCR positive persons should be based on careful clinical judgment, presence of comorbidities, social and environmental conditions of the person’s household, and presence of household members with co-morbidities associated with increased risk of severe MERS-CoV infection. 
Isolation should continue until two consecutive upper respiratory tract samples (e.g. nasopharyngeal [NP] and/or oropharyngeal [OP] swabs) taken at least 24 hours apart test negative on RT-PCR.

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