Thursday, 28 August 2014

MERS-CoV around the house-yes, it does transmit at home

Click on graph to enlarge.
Some Middle East respiratory syndrome coronavirus (MERS-CoV) questions remain stubbornly unanswered even after two and a half years.

Today comes a study from Prof Christian Drosten and colleagues, including Prof Ziad Memish, released by the New England Journal of Medicine.[1] This study takes a look at MERS-CoV infection among the contacts of MERS cases.

We already know that asymptomatic or "silent" MERS-CoV infections are not rare. At least 17% of detections of this virus have occurred in people with no overt signs or reported symptoms of disease. That's not to say that they didn't have a slightly raised temperature, headache, sniffle or something very mild that got overlooked or forgotten, but nothing noted or noteworthy. I'd love to see a study on asymptomatic MERS-CoV infected people that looked into fine detail signs and symptoms by the way-that might tell a nice little story about "silent" infections.

This new study looks at the contacts of infected cases from 26 different households, each with a single confirmed MERS-CoV infected case, with MERS. These households provided throat swabs from 280 contacts and antibody test results on at least 1 sample (only 44 permitted a second voluntary blood sample be taken-a shame) from the 280 contacts as well.

Some interesting findings included:

  • Median age of cases (65.4% male) was 55-years
  • Median age of contacts (52% male) was 29-years
  • Cases 7 household contacts (2.5%) were viral RNA-positive (RT-PCR) within 2-weeks of the index patient's illness onset. Similar to what PCR-based studies conducted previously have yielded.
  • 5 household contacts (1.7%) were considered antibody positive after a series of different tests were used. 3 were positive between 2-3 weeks after the index case's onset, and 1 each before or after that period. 
  • some indication that neutralizing antibodies against MERS-CoV might be low level and short lived in mild or asymptomatic infections and that previous antibody studies may have missed some cases if the took blood too long after a mild infection
Overall, 12 (4%) contacts acquired MERS-CoV infection from an index case, across 6 of 26 households (23.1%). 

Among others, one question I'd like answered is whether symptomatic cases being kept in home isolation, which was occurring during the Jeddah-2104 outbreak when they don't need hospital-based supportive care, is the best option for stopping transmission? We don't know whether mild or silent infections can transmit virus, which remains another important question. While 4% seems like a small proportion, it's big enough to perhaps explain some of the sporadic case occurrences. Also, we should be mindful that MERS-CoV infection is associated with the death of a third of the people it infects. I'd want to be pretty sure I wasn't letting a house-bound shedding mild/silent person spread MERS-CoV to a visiting old uncle with a co-morbidity.

References
  1. http://www.nejm.org/doi/full/10.1056/NEJMoa1405858
  2. If this is what MERS-CoV detections look like with more testing...what is the "normal" community level of virus?? [UPDATED]
    http://virologydownunder.blogspot.com.au/2014/04/if-this-is-what-mers-cov-detections.html
  3. Guidelines for home isolation related to MERS Corona Virus infections | May 2014http://www.moh.gov.sa/en/Documents/3-Isolation.pdf