WHO sees changing pattern in recent MERS cases

Recent MERS-CoV cases have featured less severe symptoms and patients who were younger and more likely to be female, but precisely what the changing pattern means is not clear, the World Health Organization (WHO) said in a new summary today.

The report came on the heels of a Saudi Arabian Ministry of Health (MOH) report of another new case, this one in a 66-year-old man in the southwestern province of Asir, who was said to be in stable condition. His illness raises Saudi Arabia's MERS-CoV (Middle East respiratory syndrome coronavirus) count to 66 cases with 38 deaths.

The MOH also announced the recovery of another patient, a female healthcare worker in Hafr Al-Batin in the northeastern part of the country. She apparently is the same patient whose case was noted by the WHO 2 days ago. The WHO listed her age as 56.

In still another development, the WHO's new emergency committee on MERS-CoV held its first teleconference today and scheduled a second session for Jul 17, the WHO said. Today's inaugural session focused on background briefings.

The global MERS-CoV tally, according to today's WHO summary and literature update, is now 80 cases and 45 deaths, which does not include the new Saudi case. That's one more death than was reported by the agency on Jul 7. WHO spokesman Gregory Hartl said the additional death was that of the Qatari patient who died in London last week after being hospitalized there since last September.

Asymptomatic cases

The WHO summary says that 16 new confirmed cases have been reported by Saudi Arabia since the last WHO summary on Jun 20, and 8 of those were reported to be asymptomatic. Four of the symptom-free cases were in female healthcare workers, while the other four were in children who had contact with other MERS patients.

Of the 80 total cases so far, 45 patients (56%) have died. Of 75 case-patients whose sex was known, 49 (64%) were male, and the median age is 51 years, the WHO reported.

When the WHO released its last MERS-CoV summary on Jun 20, the case-fatality rate was 59% (38 of 64 cases), slightly higher than the new number of 56%. Seventy-two percent of the case-patients were reported to be male at that time.

"With recent reports of asymptomatic and mild cases, the proportion of confirmed cases that have died of MERS-CoV infections is lower than previously reported, as is the average age, and the proportion of patients who are female has increased," the agency said. "It is noteworthy that these cases have been detected as part of contact investigations around severe cases."

Index case-patients in clusters are presumably more likely to have caught the virus from non-human sources and continue to be mostly older men, the report goes on to say. "Whether the relative mildness of illness in contact cases is an artifact of surveillance and case-finding activities or represents a difference in virulence between sporadic infections acquired from non-human exposures and those acquired from human-to-human transmission is unknown," it adds.

The WHO further observes that the recent mild and asymptomatic cases raise concerns about the possibility that many mild cases are going undetected. It's clear that human-to-human transmission occurs, but it's not clear if it is sustained in the community.

Two possible scenarios

"The currently observed pattern of disease occurrence could be consistent either with ongoing transmission in an animal reservoir with sporadic spillover into humans resulting in non-sustained clusters, or unrecognized sustained transmission among humans with occasional severe cases," the agency says.

To answer the questions, detailed case contact investigations, increased surveillance in other Middle Eastern countries, and studies of non-human exposures in index cases are urgently needed, it adds.

Although the worry about asymptomatic cases is that people can spread the virus unwittingly, the WHO says the public health importance of such cases is uncertain. The record of the SARS (severe acute respiratory syndrome) outbreak in 2003, also caused by a coronavirus, suggests that "very little if any transmission occurred from asymptomatic individuals."

Also, false-positive MERS-CoV tests in asymptomatic patients can result from laboratory contamination, the agency said. Serologic or other tests can provide additional confirmation in doubtful cases.

Some similar comments about the pattern of recent MERS cases were heard at a London conference sponsored by Public Health England (PHE) today, according to the conference's Twitter feed.

John Watson, MB MS, MSc, of PHE said secondary cases in clusters have tended to be milder than index cases, and the significance of milder and asymptomatic cases is not yet clear, according to conference tweets.

In other points in the WHO statement, the agency said it is preparing travel and health advice for travelers to upcoming mass gatherings. Saudi Arabia is expecting crowds of visitors this month for the Umrah pilgrimage and far more for the Hajj in October.

The WHO also said it is coordinating the collection of a set of clinical serum samples, including negative and positive ones, to standardize serologic assays. Other steps include a review of hospital infection prevention recommendations and development of advice on infection prevention for patients being cared for at home.

Emergency panel's first conference

The WHO's new International Health Regulations Emergency Committee on MERS-CoV had a 3-hour inaugural teleconference today, according to a statement from WHO Director-General Margaret Chan, MD.

The 15-member group of experts heard a review of the situation by the WHO Secretariat and briefings from representatives of several countries that have had MERS cases, Chan said. The panel decided it needs time for further discussion and consideration and decided to schedule its second conference for Jul 17.

The committee's task is to provide technical advice to the WHO on responding to MERS. Its establishment was announced last week.

See also:

Jul 9 WHO summary and update

Jun 20 WHO summary and update

Jul 8 Saudi MOH statement

Saudi MOH page with case count

PHE MERS conference information

PHE conference Twitter feed

Jul 9 Chan statement on emergency committee

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