#13,737
After not reporting any MERS cases for Epi Weeks 48 & 49, the Saudi MOH has reported 3 new cases over the past 4 days. All are middle-aged males, two reportedly had camel contact, while one does not.
As usual, the amount of detail offered is fairly limited, and we'll have to wait for WHO follow up reports to learn more.While we strive to keep track of cases, looking for any changes in patterns or trends in infections, filling the gaps in our understanding of how this virus continues to spread in the community remains a high priority.
Contact with infected camels is a known risk factor - and no doubt accounts for the continued re-introduction of the virus into the human population - but most community acquired human infections have no known recent contact with camels or camel products.While a few of these cases have had contact (usually hospital or household) with a known infected person, most do not. Exactly how, and where they were exposed remains a mystery.
One theory is that a small number of mildly symptomatic (or asymptomatic) individuals may be inefficiently spreading the virus in the community. While unproven at this time, a few recent studies on point include:
mBio: High Prevalence of MERS-CoV Infection in Camel Workers in Saudi Arabia
AJIC:Intermittent Positive Testing For MERS-CoV
JIDC: Atypical Presentation Of MERS-CoV In A Lebanese PatientSince the initial signs of MERS infection are often similar to a cold or the flu, differentiating who is - and who isn't - infected can be a extremely difficult, even for doctors used to seeing cases (see Evaluation of a Visual Triage for the Screening of MERS-CoV Patients).
Over the years, we've seen other analyses that have concluded that only a fraction of MERS cases are likely diagnosed, including:
- In November of 2013, we looked at a study published in The Lancet Infectious Diseases, that estimated for every case identified, there are likely 5 to 10 that go undetected.
- In 2015, when Saudi Arabia had recorded fewer than 1200 MERS cases, a seroprevalence study (see Presence of Middle East respiratory syndrome coronavirus antibodies in Saudi Arabia: a nationwide, cross-sectional, serological study by Drosten & Memish et al.,) suggested nearly 45,000 might have been infected.
- And a 2016 study (see EID Journal: Estimation of Severe MERS Cases in the Middle East, 2012–2016) suggested that as much as 60% of severe Saudi MERS cases go undiagnosed.
Essentially, the more thoroughly we look, the more we find.
Asymptomatic Middle East Respiratory Syndrome Coronavirus (MERS-CoV) infection: Extent and implications for infection control: A systematic review
Jaffar A.Al-Tawfiq abc Philippe Gautretd
Asymptomatic infections - once believed to be the excerption - with more comprehensive testing, now appear to be fairly common. What isn't known, however, is how well asymptomatic cases can transmit the MERS virus to others.
While this review is unable to directly answer that question, the authors do write:
ConclusionsThe good news is - despite nagging questions over the sensitivity of current surveillance and the role of asymptomatic cases in the spread of the disease - we've seen no signs of any sustained or efficient transmission of the MERS virus outside of health care facilities, and Saudi health care facilities appear to be getting better at infection control.
The proportion of asymptomatic MERS cases were detected with increasing frequency as the disease progressed overtime. Those patients were less likely to have comorbid disease and may contribute to the transmission of the virus.
The big unknown, of course, is that the MERS virus continues to evolve and adapt - and while it may not be equipped to spark a pandemic today - no one can say what tomorrow will bring.
