At least 81 U.S. healthcare workers have contracted laboratory-confirmed cases of the novel H1N1 influenza virus and about half caught the bug on the job, the Centers for Disease Control and Prevention said Thursday.
The finding is worrisome because it suggests that hospitals and workers are not taking sufficient preventive measures to limit the spread of the virus.
If a large-scale outbreak of the virus recurs this fall, a similar infection rate could cause significant problems -- not only because it would limit the number of workers available to care for the sick, but also because the infected nurses, doctors and others could transmit the virus to debilitated patients before their own symptoms become apparent. Already-ill patients would be more likely to develop life-threatening side effects from the flu.
The report in the Morbidity and Mortality Weekly Report studied 48 cases that occurred from the beginning of April to May 13, and concluded that "probably half were related to the healthcare setting," said Dr. Michael Bell of the CDC's Center for Preparedness, Detection and Control of Infectious Diseases. An additional 33 cases have been observed since then, but not studied in depth.
One of the key findings of the study, he said, is that potential patients with so-called swine flu "need to be identified at the front door" of the hospital so that personnel will know they need to take preventive measures, such as wearing masks, isolating the patients and paying particular attention to hand hygiene.
It is also "absolutely essential that healthcare personnel be vaccinated annually, for their own protection and to protect patients in hospitals," he added.
The agency is not recommending that all hospital personnel receive the antiviral drug Tamiflu, but that it be used prophylactically in personnel who have been exposed to the virus.
Agency officials are mildly surprised that the new flu virus is continuing its spread in the summer months, well after the normal end of the flu season. To date, there have been more than 17,800 laboratory-confirmed cases in the U.S., with 1,600 patients hospitalized and 44 deaths, according to Dr. Daniel Jernigan, an epidemiologist in the CDC's influenza division.
Worldwide, there have been nearly 40,000 confirmed cases in 88 countries, with 167 deaths.
In the U.S., the spread appears to be tapering off throughout most of the country but is continuing at relatively high levels in New England and New York state. And the confirmed cases may be the tip of the iceberg, Jernigan said. In areas such as New England and New York, an estimated 7% of the population has been infected, suggesting that hundreds of thousands of Americans have contracted the virus to date.
"The fact that we are seeing ongoing transmission now indicates that there is something different with the virus," Jernigan said. "It may also have to do with the complete lack of immunity among the younger population."
The spread in the Northeast may be because of cooler weather there, which favors transmission of the virus.
As schools have closed for the summer, the focus of transmission has shifted to summer camps, another place where children congregate. A Boy Scout camp in Asheville, N.C., for example, sent 19 scouts from Florida and Georgia home after they got sick and 10 tested positive for novel H1N1. Other students were quarantined.
Bell said the CDC had the same recommendations for camps as it did for schools: Sick children should be sent home and not allowed to return for a week or for 24 hours after the last symptoms disappeared.
In the week that ended June 6, the most recent period for which figures were available, 89% of laboratory tests for influenza viruses revealed the presence of H1N1. Only 1.8% of the tests revealed seasonal viruses. The rest were not sub-typed, which generally means that they were also novel H1N1.
The CDC is closely monitoring outbreaks in the Southern Hemisphere, which is now at the beginning of its flu season. Outbreaks are becoming more widespread in several places, such as Australia and Chile. Preliminary results suggest that most laboratory tests in the Southern Hemisphere are revealing the novel virus, implying that seasonal flu is being displaced.
Such findings suggest that seasonal flu may not be a significant problem during the coming winter flu season, but that the novel virus will. But Jernigan cautioned that the labs might not be looking for the seasonal virus, biasing the findings.
Virologists received a bit of a scare this week when researchers at the Adolfo Lutz Bacteriological Institute in Sao Paulo, Brazil, reported that they had isolated a mutated H1N1 virus from a patient who had recovered.
But academic researchers and scientists at the CDC discounted the report, noting that there were no changes in the portions of the virus that would alter its ability to spread or its pathogenicity.