Middle East Respiratory Syndrome-an emerging viral infection
Several news outlets, including CNN today, are carrying updates on human infections by a novel coronavirus which has been named MERS-CoV. The virus, which is related to the SARS coronavirus, has been implicated in 50 cases with a mortality rate of over 50 percent. According to the case tally at the Centers for Disease Control and Prevention, cases have been found in 7 countries throughout the Middle East and Europe; the news alert on CNN today updates this information with 3 new cases reported in Italy. MERS-CoV as the name suggests causes disease in the respiratory system, with lower respiratory involvement including fever, cough, and shortness of breath. Deaths due to MERS-CoV occurred in over half of the cases, but many of these the patients had an underlying medical condition which may have predisposed them to complications. It is not clear at this point how infection manifests itself in a generally healthy population with no underlying conditions. Because the number of individuals with potentially asymptomatic or unreported disease is not known, the exact scope of the outbreak remains an estimate. To date, all reported cases have either occurred in the Middle East, or have been in patients who reported very recent travel to the Middle East. Based on a comparison of the genome sequence of MERS-CoV with other coronaviruses, it is suspected that the virus originated in bats and has recently acquired the ability to infect humans.
Because news on this outbreak is being rapidly updated (the information this morning is more current on CNN than at the CDC), it is useful to look at some of the tools that epidemiologists and first responders might use to help officials track the spread of the virus. The CDC has published a set of case definitions that lay out the process by which possible patients should be tracked. The case definitions have come out in response to recommendations by the World Health Organization.
- Patients under investigation (PUI): individuals with acute respiratory infection (fever, cough), with likely pulmonary parenchymal involvement, travel to the Arabian Peninsula within 10 days, and no other underlying etiology for pulmonary infection (eg. S. pneumoniae, K. pneumoniae, L. pneumophila, Influenza A and B, Respiratory Syncitial Virus.) Other individuals demonstrating consistent signs and symptoms after being in contact with a PUI profile patient would also be monitored.
- Probable case: an individual fitting the above criteria, but for whom laboratory confirmation has not been completed or other the other etiologic agents above cannot be tested for AND has had contact with a laboratory confirmed case.
- Laboratory confirmed case: confirmation of the presence of MERS-CoV in a patient specimen has been accomplished by polymerase chain reaction (PCR) amplification of the virus genome. Currently, laboratory testing is being done at the CDC and other international laboratories.
The outbreak is worrisome to public health officials for several reasons. First, laboratory confirmed cases are showing a high mortality rate. Although it is unclear what the disease course looks like in an asymptomatic individual, in the elderly and other high risk populations this disease is very significant. Second, there is no cure for infection and any treatments are currently supportive in nature. Third, the virus appears to be easily spread from individual to individual, but it is not known whether it requires direct or indirect contact to do so. Several cases in May 2013 in Saudi Arabia were associated with health care workers caring for patients with the disease. Because it is not clear how the virus is spread, proper precautions with any patient fitting the at risk profile exhibiting lower respiratory involvement should be exercised!