Until relatively recently, we seldom saw in-depth reports on outbreaks of MERS-CoV come out of Saudi Arabia. Last fall, that began to change, and since then we've seen some impressively detailed epidemiological studies emerge (see EID Journal: Large Hospital Outbreak Of MERS-CoV - Jeddah, Saudi Arabia, 2014).
Today we've another example, one that looks at a very large household outbreak that occurred during May and June of 2014, spread across four homes belonging to an extended family in the town of Al-Qouz (about 400 miles south of Jeddah).
This took place at the same time (and just after) the huge Jeddah nosocomial outbreak involving several hundred cases, and at at time when reporting of cases was fragmented. Looking back, I can only find mention of a couple of these cases.
In any event, using rRT-PCR and serology, researchers identified 19 members of an extended family (n=79), who tested positive for MERS infection. Some were asymptomatic, others were mildly ill, while 11 were hospitalized (2 died).
Out of 19 cases, only 11 (58%) tested positive by rRT-PCR, a reminder that even with PCR testing, `no' doesn't always mean no.
As with any lab test, the timing of sample collection, the type of sample collected, and the handling of that sample can all affect its accuracy. The eight who tested negative by rRT-PCR were later confirmed via serology.
Since follow up testing wasn't done, it is possible that additional family members might have been infected, but had not seroconverted at the time they were tested.
The takeaway message from the authors on the lack of sensitivity of rRT-PCR testing is worth emphasizing.
This finding highlights the need for clinicians to consider MERS-CoV diagnoses in appropriate clinical settings, even in patients with negative rRT-PCR results.
I've only posted the abstract and a small snippet from the discussion, so follow the link to read the paper in its entirety.
ResearchMiddle East Respiratory Syndrome Coronavirus Transmission in Extended Family, Saudi Arabia, 2014
Risk factors for human-to-human transmission of Middle East respiratory syndrome coronavirus (MERS-CoV) are largely unknown. After MERS-CoV infections occurred in an extended family in Saudi Arabia in 2014, relatives were tested by using real-time reverse transcription PCR (rRT-PCR) and serologic methods.
Among 79 relatives, 19 (24%) were MERS-CoV positive; 11 were hospitalized, and 2 died. Eleven (58%) tested positive by rRT-PCR; 8 (42%) tested negative by rRT-PCR but positive by serology.
Compared with MERS-CoV–negative adult relatives, MERS-CoV–positive adult relatives were older and more likely to be male and to have chronic medical conditions. Risk factors for household transmission included sleeping in an index patient’s room and touching respiratory secretions from an index patient. Casual contact and simple proximity were not associated with transmission.
Serology was more sensitive than standard rRT-PCR for identifying infected relatives, highlighting the value of including serology in future investigations.
DiscussionThis investigation defined the epidemiology of a large family cluster of MERS-CoV infection in Saudi Arabia, identified multiple possible household transmission risk factors, and highlighted the useful role of serology in describing the extent of family clusters and spectrum of illness. For approximately half (42%) of the 19 MERS-CoV–infected family members, rRT-PCR results were negative while they were ill or after recognized exposure, and infection was diagnosed only retrospectively by serology; this included patients tested during extended hospitalizations and demonstrates real-world limitations in rRT-PCR or timing of specimen collection, transport, and testing.
This finding highlights the need for clinicians to consider MERS-CoV diagnoses in appropriate clinical settings, even in patients with negative rRT-PCR results. Clinicians should consider obtaining lower respiratory tract specimens to improve the sensitivity of rRT-PCR, particularly if nasopharyngeal and oropharyngeal test results are negative and clinical suspicion is high, and they should consider follow-up serologic testing. Most importantly, clinicians should apply appropriate infection control practices for patients with clinically suspected illness, regardless of initial rRT-PCR results.