MERS-CoV: Different From SARS, Comorbidities May Be Key

Laurie Barclay, MD

July 25, 2013

Middle East respiratory syndrome caused by novel coronavirus (MERS) varies widely in clinical presentation and can cause substantial mortality in hospitalized patients with medical comorbidities, according to the largest case series to date.

Abdullah Assiri, MD, from the Global Centre for Mass Gatherings Medicine and the Infection Prevention and Control Program, Public Health Directorate, Ministry of Health, Riyadh, Saudi Arabia, and colleagues report the data in an article published online July 26 in the Lancet Infectious Diseases.

"Despite sharing some clinical similarities with SARS (eg, fever, cough, incubation period), there are also some important differences such as the rapid progression to respiratory failure, up to 5 days earlier than SARS," senior author Professor Ziad Memish, MD, deputy minister for public health, Saudi Arabia, said in a news release.

SARS appeared to be much more infectious, particularly in healthcare settings, and preferentially affected healthier and younger persons, whereas MERS has higher mortality (60% of patients with coexisting chronic illnesses vs 1% - 2% for SARS).

"Although this high mortality rate with MERS is probably spurious due to the fact that we are only picking up severe cases and missing a significant number of milder or asymptomatic cases, so far there is little to indicate that MERS will follow a similar path to SARS," Dr. Memish said.

As previously reported by Medscape Medical News, a hospital outbreak of MERS caused significant morbidity and 65% fatality.

Study Design and Findings

The present report describes epidemiologic, demographic, clinical, and laboratory features of 47 MERS cases (46 adults, 1 child), confirmed with real-time reverse transcription-polymerase chain reaction. To identify knowledge gaps and define research priorities, the investigators analyzed data from these sporadic, household-associated, community-associated, and healthcare-associated MERS cases reported in Saudi Arabia between September 1, 2012, and June 15, 2013.

The majority of patients were male (77% male). Case-fatality rate was 60% overall but increased with increasing age. Of the 47 cases, only 2 were previously healthy, and 45 (96%) had underlying comorbid medical conditions, which is a substantial difference with SARS. Comorbidities included diabetes (68%), hypertension (34%), chronic cardiac disease (28%), and chronic renal disease (49%).

Presenting symptoms included fever (98%), fever with chills or rigors (87%), cough (83%), shortness of breath (72%), myalgia (32%), diarrhea (26%), vomiting (21%), and abdominal pain (17%).

Chest radiography was abnormal in all cases, ranging from subtle to extensive unilateral and bilateral abnormalities. Laboratory abnormalities included elevated lactate dehydrogenase (49%), thrombocytopenia (36%), lymphopenia (34%), and elevated aspartate aminotransferase (15%).

Clinical Implications

"The recent identification of milder or asymptomatic cases of MERS in health care workers, children, and family members of contacts of MERS cases indicates that we are only reporting the tip of the iceberg of severe cases and there is a spectrum of milder clinical disease which requires urgent definition," coauthor Professor Ali Zumla, from University College London, United Kingdom, stated in the news release. "Ultimately the key will be to identify the source of MERS infection, predisposing factors for susceptibility to infection, and the predictive factors for poor outcome. Meanwhile infection control measures within hospitals seem to work."

The investigators note major knowledge gaps regarding epidemiology, community prevalence, and clinical spectrum of MERS. Limitations of this study include patient self-selection, retrospective record review, comorbidity data unavailable for admissions without MERS, and missing follow-up data.

In an accompanying comment, Professor Christian Drosten, MD, from the University of Bonn Medical Centre, Germany, compares MERS and SARS. He notes that both viruses trigger fever, but patients lack upper respiratory symptoms. "A striking difference to SARS is the high rate of underlying comorbidity in patients with MERS," he writes. Yet without community-based data, he says researchers cannot be sure MERS will be limited to individuals with underlying disorders.

"To ascertain relevant data for MERS epidemiology, we need to develop serological assays using samples from well-defined groups of patients, such as described here," Dr. Drosten writes. "Population-based antibody testing could establish the extent of MERS-CoV infection, instead of only seeing the tip of the iceberg represented by cases admitted."

This study received no funding. The authors and commentator have disclosed no relevant financial relationships.

Lancet Infect Dis. Published online July 25, 2013.

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