MERS-CoV: Long Incubation May Require Longer Quarantine

Laurie Barclay, MD

May 30, 2013

Two cases of Middle East Respiratory Syndrome coronavirus (MERS-CoV) in France suggest a longer incubation period than previously thought, according to a clinical study published online May 29 in the Lancet. The investigators therefore suggest that longer quarantines are needed to exclude infection among patient contacts.

"Human infection with [MERS-CoV] was first identified in Saudi Arabia and the Middle East in September, 2012, with 44 laboratory-confirmed cases as of May 23, 2013," write Benoit Guery, MD, PhD, from Hôpital Calmette, Lille, France, and colleagues from the MERS-CoV study group. "We report detailed clinical and virological data for two related cases of MERS-CoV disease, after nosocomial transmission of the virus from one patient to another in a French hospital."

MERS-CoV is similar to the pathogen responsible for the SARS outbreak of 2002 and 2003. Although most MERS-CoV cases have been seen in Saudi Arabia and other Middle Eastern countries, some were found in the United Kingdom and France in persons who had travelled to the Middle East.

Both patients in this report presented with fever, chills, and myalgia and had underlying immunosuppressive disorders. The first patient, who also presented with diarrhea, had traveled to Dubai in April 2013. The second patient is a resident of France and did not travel abroad.

Both patients rapidly developed respiratory symptoms, with acute respiratory failure requiring mechanical ventilation and extracorporeal membrane oxygenation, as well as acute renal failure. The first patient died on May 28 from refractory multiple organ failure.

Using real-time reverse-transcriptase polymerase chain reaction targeting the regions of the MERS-CoV genome, the investigators tested nasopharyngeal swabs, bronchoalveolar lavage, sputum, whole blood, plasma, and serum specimens.

Lower respiratory tract specimens had high viral load of MERS-CoV (eg, cycle threshold values of 22.9 for upE and 24 for Orf1a for bronchoalveolar lavage from patient 1 and values of 22.5 for upE and 23.9 for Orf1a for induced sputum from patient 2). However, nasopharyngeal specimens were weakly positive or inconclusive.

The 2 patients had shared the same room for 3 days, and the investigators estimated that for the second patient, the incubation period was 9 to 12 days. Although hospital staff used no specific protective measures before the diagnosis of MERS-CoV was suspected, there was no documented secondary transmission.

"Patients with respiratory symptoms returning from the Middle East or exposed to a confirmed case should be isolated and investigated for MERS-CoV with lower respiratory tract sample analysis and an assumed incubation period of 12 days," the study authors write. "Immunosuppression should also be taken into account as a risk factor."

"Our findings suggest that the virus's incubation period could reach 9–12 days, a longer period than what was previously recorded, with clinical implications for the duration of quarantine," the study authors conclude. "Our results also suggest that the best samples to detect the virus are those from the lower respiratory tract, rather than nasopharyngeal samples."

This study was supported by the French Institute for Public Health Surveillance, Labex Integrative Biology of Emerging Infectious Diseases, and the European Community's Seventh Framework Programme. The study authors have disclosed no relevant financial relationships.

Lancet. Published May 29, 2013. Full text

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