WHO cites severe H1N1 cases as southern outbreaks wane

Aug 28, 2009 (CIDRAP News) – Novel H1N1 influenza outbreaks are starting to wane in the southern hemisphere, and while most cases are still mild, clinicians are reporting some severe cases of viral pneumonia in young, previously healthy people, the World Health Organization (WHO) said today.

Meanwhile, the US Centers for Disease Control and Prevention (CDC) said today that US flu activity remains low overall but appears to be increasing in the Southeast. The agency also reported five more deaths linked to the novel virus in children.

The WHO said the novel H1N1 virus has become the dominant flu strain in most of the world. In a weekly update, the agency said most southern hemisphere countries, including Chile, Argentina, New Zealand, and Australia, have passed their peak of flu activity, but South Africa and Bolivia are still seeing high levels of flu.

Elsewhere, tropical countries are seeing increasing or sustained high levels of H1N1, while temperate areas of the northern hemisphere have low activity overall, punctuated by localized outbreaks. But in Japan, "the level of influenza activity has passed the seasonal epidemic threshold, signaling a very early beginning to the annual influenza season," the WHO said.

The novel virus continues to distinguish itself from seasonal flu by causing severe cases and deaths mainly in people younger than 50, the agency noted.

"Perhaps most significantly, clinicians from around the world are reporting a very severe form of disease, also in young and otherwise healthy people, which is rarely seen during seasonal influenza infections," the WHO said. "In these patients, the virus directly infects the lung, causing severe respiratory failure. Saving these lives depends on highly specialized and demanding care in intensive care units, usually with long and costly stays."

The agency listed an overall H1N1 death toll of 2,185 today, but it offered no estimate of how many severe cases or deaths involved viral pneumonia in young people.

The WHO statement appears to fit with findings reported by a French researcher this week from H1N1 infection and death rates on two islands—the French territory of New Caledonia and the nation of Mauritius. The researcher, Antoine Flahault, said it appears that viral pneumonia, as opposed to secondary bacterial pneumonia, is far more common as a cause of death in H1N1 flu than in seasonal flu, according to an Aug 24 Agence France-Presse report.

A CDC official said today that the agency does not have an estimate of how many severe cases of H1N1 viral pneumonia have occurred in the United States.

"We certainly have seen serious pneumonia, including in previously healthy people, just like in the WHO report, but I don't have a good way to tell how many there have been," Dr. Anthony Fiore, a medical epidemiologist in the CDC's influenza branch, told CIDRAP News.

The CDC reported today that the nation has had 8,843 hospitalizations and 556 deaths linked to the novel virus, up from 7,983 hospital cases and 522 deaths reported a week ago.

The WHO said several countries in the southern hemisphere have viewed the need for intensive care as the greatest burden on the healthcare system during the current flu season. Some cities reported that close to 15% of hospitalized patients needed intensive care.

In other observations in today's reports, the WHO said:

  • Early studies show a higher risk of hospitalization and death among minority groups and indigenous populations—four to five times higher than the general population in some studies.
  • Early data from two countries suggest that people infected with both HIV and novel H1N1 are not at increased risk for severe illness, provided they are on antiretroviral therapy.
  • H1N1 viruses from all outbreaks are virtually identical, showing no signs of dangerous mutations.

The CDC, in its flu surveillance report for the week that ended Aug 22, said flu activity remained stable or declined in most parts of the country, but it appeared to increase in the Southeast. The jurisdictions reporting widespread activity were Alaska, Georgia, and Puerto Rico.

Five pediatric deaths linked to H1N1 illness were reported last week, bringing the total to 42, the CDC said. The deaths occurred between Jun 7 and Aug 15 in California, Georgia, Illinois, and Texas.

The CDC also said the number of cases of oseltamivir (Tamiflu)-resistant H1N1 infection has reached seven, up from four a week earlier. Six of the seven patients had received oseltamivir for either treatment or prophylaxis.

The WHO said that among the handful of oseltamivir-resistant H1N1 cases identified worldwide, no instances of onward transmission of resistant viruses have been found so far.

See also:

WHO briefing note

WHO weekly update

Jun 29 CIDRAP News story "Novel H1N1 flu can cause severe respiratory illness"

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