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PCR Confirmations In Asymptomatic HCWs & Children
The ministry also announced monitor virus in عاملتين of صحيتين in the eastern region and Hasa and they show no symptoms also,
The above translation from the June 23 Kingdom of Saudi Arabia Ministry of Health (KSA-MoH) update describes six more asymptomatic confirmed MERS-CoV cases. Two of the cases are health care workers (HCWs) from nosocomial outbreaks in Al Hasa, as well as a second location in the eastern province. These are in addition to the two asymptomatic HCW cases in Taif, which is in the western region of KSA and adjacent to Mecca (see map). The asymptomatic cases in Taif are in addition to a mild MCW case and two fatal cases in sisters (65F and 68F) in Taif, signaling a nosocomial outbreak in the west.
In addition, the four confirmed MERS-CoV cases in asymptomatic children who are contacts of cases in Riyadh and the eastern region are the first such cases reported. The reasons for the dramatic increase in confirmed asymptomatic cases is unclear.
WHO reported the asymptomatic and mild HCW cases in Taif as “weak positives”, which was the terminology used to describe PCR positives in asymptomatic contacts in Italy, which included at least five HCWs A second lab failed to confirm the weak positives, but different primers were used, raising the possibility that the first set of primers was more sensitive, leading KSA to switch primers.
A NEJM publication of the large nosocomial outbreak in the eastern region described a super spreader and multiple long transmission chains similar to those reported for SARS coronavirus in 2003. However, the NEJM report also cited 11 probable cases who developed pneumonia and were contacts of confirmed cases but were not confirmed (either because they were not tested or tested negative one time). The failure to detect MERS included fatal cases that included the index case and the super spreader, signaling serious sensitivities issues. This may have prompted a change to more sensitive PCR primers and the detection of the asymptomatic cases.
Alternatively, the NEJM paper included full sequences of four of the nosocomial cases generated through a collaboration between the Welcome Trust and the KSA-MoH. This relationship may have led to sequencing of inserts from PCR tests which proved that the weak positives were true positives, leading to an explosion of confirmed asymptomatic cases which increased the total from 0 to 8 in the past two days.
As expected these new cases led to a plummet in the case fatality rate for cases with outcomes, which has fallen from 82% (32/39) to 63% (34/54).
More detail on KSA-MoH PCR testing would be useful.