Washington — Scientists from around the world met in a virtual conference about the novel H1N1 outbreak. The call, hosted by the World Health Organization (WHO) on May 5, is the second international technical meeting held since disease surveillance efforts in Mexico began detecting cases of influenza-like illness March 18.

Certainties about the rapidly moving virus have been scarce, even as WHO reported May 6 that 23 countries have officially reported 1,658 cases of H1N1 infection and 30 deaths, including a second death in the United States confirmed May 5.

But together the scientific exchanges — the first held April 29 — and open communication among the world’s health agencies are slowly producing information that will help public health officials deal with the emerging pandemic.

“This was a call in which the investigators of a number of different countries were reporting what they were seeing and their understanding of the information that they have at this time,” Dr. Keiji Fukuda, WHO assistant director-general for health security environment, said during a May 5 briefing, “and we focused the discussions primarily on clinical illness.”

PROFILING THE ILLNESS

Countries are continuing to report new cases, Fukuda said. Mexico has reported 822 laboratory-confirmed cases of infection, including 29 deaths. In the United States, the Centers for Disease Control and Prevention (CDC) reports 642 confirmed human infections in 41 states, another 845 probable cases and two deaths, both in Texas.

The following countries have reported confirmed cases (as of May 6) but no deaths: Austria (1), Canada (165), China (1), Colombia (1), Costa Rica (1), Denmark (1), El Salvador (2), France (4), Germany (9), Guatemala (1), Ireland (1), Israel (4), Italy (5), Netherlands (1), New Zealand (6), Portugal (1), South Korea (2), Spain (57), Switzerland (1) and the United Kingdom (27).

The average age range of those who are being infected seems to be the mid-20s. This is in contrast to the age range in seasonal flu, which tends to infect the very young and the very old.

Investigators do not yet know the reason for H1N1 infections in young people, Fukuda said, but this could include the possibility that younger people were traveling in Mexico when the outbreak began and the infection could spread over time to older people, or that older people have some protection from H1N1, either from earlier flu infections or for some other reason.

Other observations from the meeting include the following:

• The H1N1 incubation period seems to be from one to five days, similar to seasonal flu.

• Infected people are developing generally milder illness, more like the seasonal flu, despite the fact that some of the earlier cases in Mexico seemed more severe. Several countries are reporting severe illness in some patients, but investigators do not yet know how often this is happening, Fukuda said.

• The viruses that are being studied in different locations “look pretty similar,” he said.

The WHO pandemic phase is still at 5, a strong signal that a pandemic is imminent and a notice to countries that it is time to organize, communicate and implement planned mitigation measures. The level could be elevated to full pandemic phase 6 if community transmission of the virus becomes more widespread.

“Right now we do not believe we are seeing community transmission [in other countries] in the same way we are seeing community transmission in the United States or Mexico,” Fukuda said.

“When we talk about community transmission,” he added, “what we are really looking for is transmission not just in institutions but out in the broader community. We do not feel that we are seeing that right now. We will continue to work closely with the countries and any other countries reporting cases to make sure that we feel that we have a good handle on that situation.”

SOUTHERN HEMISPHERE

Flu viruses thrive in cold weather, and countries in the Southern Hemisphere are just moving into their autumn season, which runs from about March 10 to May 31 each year. The coldest average temperatures occur in July.

To date, one country there, New Zealand, has reported six confirmed cases of H1N1. International public health officials say they are closely monitoring seasonal and H1N1 activity there.

“Most of the infections right now are located in North America. There are infections that have gone to other countries in Europe, Asia and South America, but most of the infections have still been in North America,” Fukuda said.

“When you look at the map you see that there are no large outbreaks reported in the Southern Hemisphere, but I think this is still very early in the spread of this virus,” he added. “The Southern Hemisphere is entering into the winter months and this is one of the areas we want to monitor most closely because it is quite possible that we will see activity there.”

The burden of diseases such as HIV/AIDS and tuberculosis in some developing countries in the Southern Hemisphere, including many African countries, will complicate the H1N1 infection and potentially accelerate it.

“The world is made up of a large number of groups of people who have different medical conditions. [Meeting participants] talked about how chronic heart or lung conditions make people more vulnerable to influenza viruses in general,” Fukuda said.

“We know that people who have HIV infections can be susceptible to a number of other infections and with influenza viruses HIV-infected populations are one of the groups of people who can be somewhat more heavily impacted than people who are healthy,” he said. “This is another reason for us to monitor very carefully what is going on as this infection spreads.”