New reports yield clues about H7N9 detection, links to poultry

May 16, 2013 (CIDRAP News) – Though the steady stream of new H7N9 cases has tapered, the pace of publications on the new virus is still brisk, with new reports today on Taiwan's case, a link between markets and human cases, and risk assessment and planning for possible scenarios in Europe.

All three reports were published in today's issue of Eurosurveillance.

Lessons from Taiwan's H7N9 case
In the report on Taiwan's only case, officials from the Taiwan Centers for Disease Control wrote that they learned several useful lessons from the case involving a man in his 50s who got sick in the middle of April after traveling for work to China's Jiangsu province, where the virus had already sickened people and been detected in live-market poultry.

Within days of the announcement of the first cases in China, Taiwanese officials made H7N9 a notifiable disease and prepared for suspected cases to be detected through its influenza surveillance system, as well as the surveillance system for community-acquired pneumonia of unknown cause.

The enhanced surveillance activities helped flag the man's illness. His was the only H7N9 infection confirmed in Taiwan among 358 suspected cases and 41 severe pneumonia illnesses from Apr 3 through May 10.

The authors noted that the man did not have a cough and didn't meet the official case definition, but his doctors reported his illness as a suspected infection anyway, given his recent travel to China's outbreak area. They suggested that physicians be allowed to report suspected cases that don't fully meet case definitions.

The patient's throat swabs were negative for the H7N9 virus on day 4 and 9 after his illness onset, but an endotracheal aspirate collected on day 8 was positive for the new virus. Taiwan officials wrote that the testing experience led them to revise their sampling guidance.

No H7N9 infections have been found in any of the man's 139 contacts, including three healthcare workers who had respiratory symptoms a few days after they were exposed to the patient. The team noted the healthcare workers who had symptoms provided routine care using N95 respirators, goggles, gloves, and protective clothing.

Strong link between human cases, poultry
Meanwhile, health workers involved in outbreak response in Huzhou City, located in China's Zhejiang province, found a strong link between illnesses in 12 patients and local poultry in different settings, according to another Eurosurveillance report.

They described 12 patients whose H7N9 cases were confirmed from late March to May 10. Ages ranged from 32 to 81. Ten had underlying medical conditions such as hypertension, bronchitis, and heart disease.

Nine of the 12 patients had visited live-poultry markets within 10 days of getting sick. The three others had a history of direct contact with poultry shortly before they started having symptoms. One had culled poultry from the live markets, one had purchased live poultry from a vendor and raised them with a neighbor in a courtyard, and one was the spouse of a man who had bought live birds from a market and brought them home to raise.

Researchers collected poultry and/or environmental samples from nine poultry markets linked to the cases, the home settings where case-patients kept their birds, and seven other live-poultry markets in the area that the patients had not visited. Evidence of H7N9 was found in samples from all of the settings.

The team wrote that the findings support the hypothesis that poultry are the source of the H7N9 virus, and they noted that no new cases in Huzhou City have been reported since live markets were shuttered there in the middle of April.

A reported lack of poultry exposure in some of the earlier cases in the outbreak might stem from some patients forgetting details of their exposure history or because they are too sick to provide the details. "It may therefore be possible that patients with no documented exposure may have in fact been exposed to poultry," they wrote.

Testing of 339 close contacts found no other H7N9 infections, and although throat swabs might not yield the virus as reliably as deep sputum samples, the patients had no obvious symptoms, the authors wrote.

EU risk and planning scenarios
In the third Eurosurveillance report today, officials from the European Centre for Disease Prevention and Control (ECDC) described two scenarios they are considering as they assess the risk of H7N9 to European countries and take the next response steps.

One of the scenarios reflects the current situation in China: zoonotic spread of the disease with sporadic infections in humans who have close contact with the animal reservoir. The other is efficient human-to-human transmission of the H7N9 virus, resulting in a pandemic. The ECDC also listed 13 critical epidemiologic events that might have consequences for Europe.

Though Europe is likely to see an imported H7N9 case, it may not occur anytime soon, if the H7N9 virus shows the same warm weather decline as the H5N1 virus historically has, the officials wrote. The likelihood of an imported case could increase, however, if the outbreak area expands.

The ECDC said the likelihood of the H7N9 virus spreading to wild birds in Europe is difficult to assess, given how little is currently known about its circulation in China's wild bird population. Once validated tests are available, it will be crucial to watch for the virus in Europe's wild birds.

Likewise, the threat to Europe's domestic birds is difficult to assess, the authors said. The virus could be brought to the continent through illegal importation of live birds, but a more likely scenario would be mixing of migratory birds, which could expand the virus westward toward Europe.

With the second possibility, the virus might not arrive for several years, the ECDC officials said, noting that it took nearly a decade for H5N1 to spread from wild birds in China to the European Union.

Because the virus doesn't cause noticeable disease in poultry, statutory surveillance for low-pathogenicity viruses will become crucial for protecting human health, the ECDC officials wrote.

See also:

May 16 Eurosurveill rapid communication on Taiwan H7N9 detection

May 16 Eurosurveill rapid communication on H7N9 link between poultry and confirmed cases

May 16 Eurosurveill perspective on H7N9 triggers for EU risk assessment and planning

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