Expatriate health care workers in Saudi could disperse MERS globally, but the coronavirus still has transmission problems

March 18th, 2015

The importation of MERS into the United States via health care workers from hospitals in Saudi Arabia has cast light on the huge expatriate work force of international clinicians in the Kingdom and neighboring countries.

Even in the face of increasing MERS cases in the region, recruiting services continue to promise high salaries and tax-free compensation for a wide variety of physician posts, nursing jobs and opportunities for ancillary workers.

Given that one-third of all MERS cases thus far have occurred in health care workers, it doesn’t take a great leap of logic to see that these traveling caregivers are the emerging coronavirus’ best bet to escape the Middle East and spread globally. Indeed, if MERS was not so difficult to transmit to healthy people in the community, we would probably be having a very different conversation that would include words like “pandemic,” “quarantine” and “morgue.”

While a deadly threat to immune compromised patients in hospitals, MERS has not been able to sustain transmission in the community beyond a few reports of families and other close contacts. Many uncounted mild or asymptomatic cases may have occurred, but the point is transmission rapidly dissipates in any measurable way in the community. In the absence of a mutation making it more transmissible – which is certainly a realistic concern given the known mutability of coronaviruses -- MERS currently lacks the staying power needed for true pandemic potential. In a nutshell, it lacks the ability for sustained spread in the community between people with competent immune systems.

Last year, for example, researchers compared MERS to SARS using the classic epidemiological measure of reproductive ratio, the expected number of secondary infections from a single case.(1) The reproductive ratio reaches a tipping point for further transmission at 1 or above, indicating secondary infections can sustain an outbreak. Researchers looked at 55 laboratory-confirmed cases of MERS, finding that even in their most “pessimistic scenario,” that MERS had a reproductive ration of .69. They noted that pre-pandemic SARS was in the .80 range, but that coronavirus did apparently mutate and become more transmissible at some point in the outbreak.

Reference

1.Breban R, Riou J, Fontanet A. Interhuman transmissibility of Middle East respiratory syndrome coronavirus: Estimation of pandemic risk. Lancet Early Online Publication, 5 July 2013 doi:10.1016/S0140-6736(13)61492