In the first 2 weeks in April, cases of infection with an untypable influenza A virus began to be identified in Mexico and southern California.1 Although the exact sequence of events is uncertain, by the third week of April it was established that the illness resulted from a triple recombination of human, avian, and swine influenza viruses; the virus has been found to be H1N1. This virologicanalysis allowed for the development of a polymerase-chain-reaction (PCR) test to determine whether, in any given person, illness with the protean manifestations of cough, fever, sore throat, diarrhea, and nausea could be confirmed as a case. Armed with this critical tool, clinicians and epidemiologists are able to make case assignments to define and track the outbreak and to determine diseaseseverity.
Health authorities from around the world formulated plans for monitoring and controlling this outbreak. On May 7, 2009, just about a month after the first case of this new H1N1 influenza was recognized, we are publishing articles providing background information about novel recombinant forms of H1N1 influenza causing human disease in the United States and a summary of the outbreak casesreported in the United States as of May 6.
Our goal in publishing these articles is to provide clinical descriptions of patients with the condition so that health professionals can use this information in making the difficult decision about whether an individual patient has a suspected case. This decision will depend on the presence of typical, but unfortunately variable and nonspecific, symptoms;an epidemiologic link to other known suspected or established cases (though this may become less useful as the infection becomes widespread throughout the population); and, where appropriate, a positive identification of the H1N1 virus by the PCR test (see video for the correct method of obtaining a nasal sample). Making informed decisions is important for several reasons. First, crediblesuspected cases should trigger public health measures such as contact tracing and quarantine — which will benefit the community — and consideration for treatment with neuraminidase inhibitors, which will potentially benefit the individual patient. Obviously, if we assign suspected-case status to more people than belong in this category, we alarm the public and create hardship for many who will turn out tobe influenza-negative. If we miss suspected cases and the affected people circulate in the community, the illness will spread more rapidly. Finding the right balance will be difficult, but our efforts should be guided by the data as they emerge. The ability to clearly define a confirmed case will also allow for a careful assessment of the associated illness and its severity.
We now haveimportant tools with which to fight this outbreak: a clear case definition, an aware health care system, and an informed public. We await the availability of a vaccine, which will require several months to prepare.
Although it has been just over a month since the first cases were identified, it seems unlikely that this outbreak will lead to widespread, severe illness and deaths. However, this may bejust the first wave, and we will carefully monitor this outbreak. To help in this process, we have established the H1N1 Influenza Center at NEJM.org, which is open and available to all. We will post original research and other articles, as well as Journal Watch summary and commentary on important articles that may appear elsewhere. We have also posted historical pieces from our archive on the"swine flu" epidemic of the 1970s and the 1918 influenza epidemic. The H1N1 Influenza Center will also have links to the most up-to-date news on the outbreak, including material from sources such as the World Health Organization and the Centers for Disease Control and Prevention. One highlight is an interactive map from HealthMap showing the location of confirmed and suspected cases of H1N1...
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