Secondary US MERS case ruled out; Saudi count grows

Bloood draw
Bloood draw

The man's conclusive blood test -- neutralizing antibody -- confirmed that he did not have MERS., Alexander Raths / iStockphoto

An Illinois man who was thought to have caught MERS-CoV (Middle East respiratory syndrome coronavirus) from the first US MERS patient was not infected after all, the Centers for Disease Control and Prevention (CDC) announced today.

In late April the Illinois man met with a business associate who was later found to have a MERS-CoV infection. The CDC announced May 17 that the Illinois man had tested positive for MERS-CoV antibodies, suggesting that he had contracted the virus.

But more definitive serologic (antibody) tests now indicate that the Illinois man was not infected, the CDC announced today. Until today, his case was regarded as the first known secondary MERS case in the country.

In other developments, Saudi Arabia announced three more MERS cases today, two of them fatal, while the World Health Organization (WHO) reported a case in Jordan.

Three kinds of serologic tests

CDC officials announced the Illinois man's test results at a press conference and in a news release today.

The Illinois man is a business associate of an American who works in healthcare in Saudi Arabia and was diagnosed as having MERS-CoV on May 2 after he traveled to Indiana to visit relatives. The two men had face-to-face meetings on Apr 25 and 26, the first one lasting 30 to 40 minutes and the second one less, according to earlier reports.

Because of his close contact with the MERS patient, the Illinois man was contacted and tested for MERS-CoV. The CDC used polymerase chain reaction (PCR) to test a respiratory sample for active infection, and the results were negative, officials noted today.

But to be more sure of the results, CDC officials said they also ran three types of serologic tests: ELISA (enzyme-linked immunosorbent assay), IFA (immunofluorescent assay), and a neutralizing antibody assay. The last is more definitive and takes longer than the other two.

The ELISA and IFA tests were positive on May 16, and the CDC announced the findings the next day.

"This compelled us to notify and test those people with whom he [the Illinois man] had close contact in the days following his interaction with the Indiana MERS patient," said David Swerdlow, MD, leader of the CDC's MERS response, in today's press release.

"However, after CDC scientists completed the slower, more definitive test, we've concluded that the Illinois resident had not been infected with MERS-CoV," Swerdlow said at the press briefing. He noted that results of the three serologic tests "are not black and white, but require interpretation."

He also noted that no MERS-CoV infection has been found in any contacts of the first two US patients. (The second patient is a health professional who works in Saudi Arabia and tested positive for MERS after traveling to Florida in early May. Both patients have recovered.) Almost all the travelers who were on airline flights with the two men have now been tested, he said.

Erring on the side of caution

Although the testing of the Illinois man's contacts now appears to have been needless, CDC officials said today that, to protect the public's health, they would probably do the same thing again in similar circumstances.

"We'll continue to err on the side of caution when responding to cases of MERS in this country," Swerdlow said.

In response to questions, he said, "We can't wait until we have all the tests back to take public health action. . . . We have to be absolutely certain that we are protecting the public."

Responding to other questions, Mark Pallansch, PhD, director of viral diseases in the CDC's National Center for Immunization and Respiratory Diseases, said the three types of serologic tests are done "on a specific schedule," with ELISA first, and not concurrently. The neutralizing antibody test takes 5 days.

He allowed that it might be helpful in some circumstances to start the neutralizing antibody test right away, but said the test is time- and labor-intensive and can't be routinely used on all specimens.

"The neutralization test uses live MERS virus and therefore must be done in a high containment lab," Pallansch said. "It's not simple to immediately test hundreds of samples in that environment."

In other comments, Swerdlow said the absence of infection in the Illinois man doesn't mean that MERS-CoV could not spread with the level of contact he had with the patient. However, "It was a little reassuring that this contact did not lead to transmission," he said.

In response to a question about their level of confidence in the PCR test for MERS-CoV, Swerdlow said, "Wecertainly think the PCR is good, but we don't have the kind of ongoing information that you'd have for tests used for years and years."

He said contacts of the MERS patients have been tested with PCR twice—initially and at the end of the expected viral incubation period. "We don't like to take any chances in these kinds of circumstances," he commented.

Pallansch said a possible explanation of the false-positive results in the initial serologic tests is that the man had antibodies to other coronaviruses, leading to cross-reactions.

The officials said the CDC will continue to evaluate the MERS-CoV tests in use and will be developing new ones.

Latest Saudi cases

Meanwhile, the three MERS cases reported by Saudi Arabia today included one in Riyadh and two in Mecca. Today's announcement came after 2 days without any new cases in the country.

The Riyadh case involves a 72-year-old man who got sick on May 5 and was hospitalized on May 26 but is now in stable condition in home isolation, the Ministry of Health (MOH) said.

The two cases in Mecca were both fatal. The patients were a 65-year-old man and a 39-year-old woman, both of whom had several preexisting conditions and had prior contact with other MERS patients.

The MOH also announced four deaths in previously diagnosed MERS patients, two men in Medina and two women in Riyadh. Their ages ranged from 36 to 80. Four other patients—three in Riyadh and one in Taif—have recovered, the ministry said.

With the latest developments, Saudi Arabia's MERS count climbed to 565 cases and 186 deaths.

WHO announces Jordan case

In other news, the WHO today described another case in Jordan, in a 69-year-old man who lives in Amman governorate. The details don't seem to match up with a Jordanian case reported by the media earlier this week, but the information on that case was very sparse.

The WHO said the Amman man was hospitalized for surgery from Apr 29 to May 3, and 5 days later he sought treatment for a fever. He was hospitalized again May 11. Two days after that, he tested negative for MERS, but a chests x-ray showed pneumonia. On May 23 another MERS-CoV test came out positive.

The patient, who has preexisting conditions, is in critical condition and under intensive care. He has no history of recent travel, contact with animals, or contact with other MERS patients. But he is in a hospital where an earlier MERS case-patient was admitted, the WHO said.

The lack of a travel history contrasts with information about the Jordanian case reported earlier this week. A media report about that case said the patient was hospitalized a week after returning from a trip to the "Holy Land."

The Jordan case increases the WHO's MERS count to 636 cases with 193 deaths.

See also:

May 28 CDC press release

May 28 CDC teleconference transcript

May 28 MOH statement on latest cases

May 28 WHO statement on Jordan case

May 17 CIDRAP News story on suspected case in Illinois man

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