Federal health officials today said blood tests have found evidence of infection in an Illinois man who had close contact with the patient who had the United States' first case of imported Middle East respiratory syndrome coronavirus (MERS-CoV).

This represents the nation's first known secondary infection in ongoing investigations into illnesses involving two health professionals, the other one from Florida, who became ill after traveling from Saudi Arabia.

The Illinois man met with the patient twice in a face-to-face business setting shortly before the first patient's illness was detected, the US Centers for Disease Control and Prevention (CDC) said today. The first patient, who had worked in a Riyadh hospital before traveling to the United States, was admitted to an Indiana hospital on Apr 28, where his illness was confirmed May 2. He was released from the hospital on May 9.

At a media briefing today, David Swerdlow, MD, who leads the CDC's MERS response, said the case sheds more light on the spectrum of the disease and its transmission patterns. "We still don't think this virus transmits easily, but it does transmit," he said.

Swerdlow said the Illinois man met with the Indiana patient on Apr 25 once for 30 to 40 minutes, then met with him again briefly on Apr 26. The Indiana patient had traveled back to Illinois by car to see his business associate and was sick with fever and muscle aches during the meeting, though he reportedly didn't have respiratory symptoms at that time. The two men shook hands and were within 6 feet of each other.

Swerdlow said health officials were concerned enough about the level of contact the two had to place the Illinois man among the group of 60 close contacts of the Indiana man that health officials have been following with testing and health monitoring.

During the follow-up investigation, local health officials contacted the Illinois man on May 3 and tested him for active MERS infection May 5. Public health workers have also been monitoring his health, and though he had mild coldlike symptoms, he has not sought or received medical care.

Initial tests were negative, but health officials have been collecting blood samples from close contacts of the Indiana patient to check for asymptomatic infections. Late last night preliminary blood tests showed that the Illinois man had developed antibodies to the MERS virus and had likely been infected by the Indiana patient, the CDC said.

The Illinois man was previously healthy, is feeling well, and has been on home isolation since early May, which Swerdlow pointed out has limited his number of contacts. He said health officials are now monitoring and testing that man's contacts, using the same protocols they did for the patients in Indiana and Florida.

Transmission risk considerations

Most MERS infections have occurred in the Middle East or have been directly linked to a case in that region. Though sporadic imported cases have been occurring since early in the outbreak, secondary infections have been more rare but did occur after primary cases were detected in the United Kingdom, France, and Tunisia.

Global and national health officials have said the risk of secondary infections is low and limited mainly to people who had unprotected, close contact with MERS patients, such as family members or healthcare workers. Today's CDC announcement raises questions about the level of contact that puts people at risk, with a business meeting presumably reflecting a lower level of contact than a care-giving scenario involving a sick family member or hospital patient.

Swerdlow told reporters that the virus still doesn't appear to spread among humans easily in a sustained way, but he added that aggressive testing will not only help flesh out transmission patterns but also reveal more about what appears to be a broader range of severity for the disease, from no symptoms to severe and sometimes fatal pneumonia. "We don't understand a lot about how the virus is transmitting, so we're casting a wide net, hoping to learn more," he said. "Our most important point is that doctors should be vigilant."

"We don't think this changes the risk to the general public or public health practices," Swerdlow said.

The Illinois man's illness, though considered the third US infection, won't be reflected in the global MERS count, because positive serology results aren't included in the World Health Organization (WHO) case definition for MERS, Swerdlow said.

Michael T. Osterholm, PhD, MPH, director of the University of Minnesota's Center for Infectious Disease Research and Policy, publisher of CIDRAP News, said one case doesn't change the picture and the event is consistent with other examples of MERS spread.

Though the risk of transmission still appears to be low, he said there's a lot that is still not known about the disease—for example, whether some patients are "super shedders" who are more likely to transmit the disease to others. Osterholm has traveled to the Middle East to consult on the MERS outbreak.

"All of us should be more careful to describe the risk to the public," Osterholm said, adding that the message should be balanced and not "oversell" a lack of risk.

Saudi Arabia reports nine cases, five deaths

In other MERS developments today, Saudi Arabia's ministry of health (MOH) announced nine new cases along with five more deaths, all from areas that have been the epicenters of the outbreak during a surge of infections that began in March.

Jeddah and Medina reported three cases each, two infections occurred in Riyadh, and one was in Mecca. All patients are younger or middle-aged adults, and only one was reported to have an underlying medical condition. Two are in critical condition, six are listed as stable, and one is asymptomatic.

Illness onsets range from Apr 27 through May 16, and hospitalization admission dates range from May 2 to May 16.

Only one patient, a 36-year-old woman from Riyadh who has an asymptomatic infection, was reported to have had contact with a MERS patient. No other exposures, such as contact with camels or animal environments, were listed for the other patients.

Health experts who were part of a recent WHO mission to Saudi Arabia said healthcare-acquired infections appear to be amplifying what may be a seasonal increase in MERS. However, over the past several weeks, the Saudi officials have not said whether any of the infected patients are healthcare workers.

Some unusual details were listed for three of today's patients. One is a 33-year-old woman from Jeddah who first started having respiratory symptoms on Apr 27 and was admitted to the hospital on May 2. The first two rounds of MERS tests were negative, but the third-round tests were positive.

In two other cases, patients left health facilities in Medina but were then hospitalized, one of them after initially refusing to be tested. One is a 36-year-old man who was admitted to the hospital on May 13 after coming down with a fever but was discharged against medical advice on May 15. He was readmitted to another hospital the next day.

The other patient, a 37-year-old man, started having respiratory symptoms on May 6 and visited an emergency department on May 10, where he refused to be tested for MERS. On May 16 he was admitted to another hospital where he is receiving treatment in the intensive care unit).

Fatal cases announced today include patients whose illnesses were reported earlier, between Apr 23 and May 14. All of them were adults aged 55 to 80 years old. One of the patients died on May 11 and the other four died on May 16.

Today's announcement bumps Saudi Arabia's MERS total to 529 cases 168 deaths from the disease.

See also:

May 17 CDC press release

May 17 Saudi MOH statement on 9 cases

Saudi MERS page with case count

CDC MERS guidance for health professionals