H1N1 Influenza Cases Worldwide Now at 2500; Southern Hemisphere Cases Reported

Neil Osterweil

May 08, 2009

May 8, 2009 — The World Health Organization (WHO) is holding the line, keeping the global influenza A (H1N1) pandemic alert level at phase 5, which indicates that a pandemic is expected but has yet to be officially declared.

As of 8:00 am EDT, there were 2500 laboratory-confirmed cases of swine-origin influenza A (H1N1) from 25 countries, with the numbers of deaths remaining at 44 — 42 in Mexico and 2 in the United States, said Sylvie Briand, MD, acting director of the Global Influenza Program at WHO, during a media briefing.

For the first time, cases have been reported from the southern hemisphere, with 4 confirmed cases in Brazil.

"However, [although] we see this increase in the number of cases, we still remain in phase 5, which means that we have no evidence of community transmission. We have new cases, most of them are imported cases from returning travelers or close contacts of these people," Dr. Briande said.

Dr. Briand heads a science, knowledge management, and standards group at WHO made up of experts in infection control, clinical management, occupational health, environment, and other disciplines. On Thursday May 7, her team held a conference call with health authorities in Mexico to try to get a better idea of which patients are at high risk in the current outbreak.

They conducted a case-by-case review of the most serious cases in the Mexican outbreak, and they identified 2 groups of people who developed severe illness.

The first group includes previously healthy young people who experienced a rapid deterioration of health status; most of these patients died from acute viral pneumonia.

A second at-risk group includes patients with chronic conditions such as diabetes, tuberculosis, and cardiovascular disease. Such patients are typically at increased risk for complications and death from seasonal influenza as well, Dr. Briande noted.

The Mexican physicians reported that viral pneumonia progressing into acute respiratory distress, rather than acute bacterial pneumonia, was the most common presentation.

The primary causes of death were respiratory failure and major organ failure.

"We understand that the disease is mild in the majority of cases; however, we will have some serious cases, mostly in people with underlying conditions, which is close to the pattern we see in seasonal influenza. But we can expect also some cases in people who were previously healthy and will suffer from this virus directly," Dr. Briande said.

She noted that the young, previously healthy people who died from viral pneumonia in Mexico were among the first patients to present, before the nature of the outbreak was fully understood, and they tended to seek medical help only when they were very ill, late in the course of the disease.

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