For the second week in a row, the state health department is reporting decreased H1N1 activity in Utah, but officials aren't yet willing to call it a sustainable trend.

There were no deaths reported for the week ending Nov. 7, and 103 hospitalizations were logged, but only 37 actually occurred during that week, while 66 occurred prior to Nov. 1 but were not reported until the most recent week.

Dr. Robert Rolfs, state epidemiologist, said he doesn't know whether the coming cold weather will send H1N1 levels back up.

"It's unlikely that we've gotten to the level of immunity in the population that we can be sure we won't have another outbreak, but when and whether that happens is completely unknown. I am encouraged that the level of flu is still going down," he said, though the rate of disease is still above the "epidemic" threshold.

Rolfs said the decline wasn't just in numbers of deaths and hospitalizations, but in the number of cases being seen by health-care clinics throughout the state.

"We do a weekly call with them, and that's what they said on Tuesday. The proportion of visits for influenza-like illness are down," he said. Diseases rates at this point "are about half of what we saw a few weeks ago."

As for a relationship between cold weather and flu, Rolfs said in tropical climates "they tend not to have outbreaks, but the disease is just sustained at something lower than the outbreak level."

In temperate zones like the Wasatch Front, "we have outbreaks that are quite distinct. Cold, dry air is more favorable to the virus," he said.

"It clearly happens in the winter, but I wouldn't want to say the reason it's going down is because it has been warmer. It's quite possible we'll have another wave of this. We really just don't know when."

Rolfs said Utah is unique in the number of older people contracting H1N1.

"We're seeing somewhat more serious disease among the older population, and we're trying to figure out what that means," he said. "It's not enough that we would change our priority status (for who can now get the H1N1 vaccination) but we've talked to the CDC about it."

The national Centers for Disease Control and Prevention hasn't seen as much illness in the older population as the Beehive State has, he said. When older Utahns do get H1N1, "they are in the target group to receive the anti-virals" like Tamiflu and Relenza, which shorten the flu's duration if given within 48 hours.

"They have a lower attack rate (of contracting the virus) but a much higher incidence of getting seriously ill if they do get it," Rolfs said.

Obesity is another category showing higher than expected illness in Utah, he said.

"The problem with depending on that is obesity is associated with a bunch of conditions like diabetes and lung disease that also put you at risk," Rolfs said. Researchers at Intermountain Healthcare are currently examining obesity as a risk factor for H1N1. At this point, there is not enough evidence to make obesity, in and of itself, a risk factor.

"I personally think at some point it will be proven to be a risk factor, but I don't think we have enough information to answer that yet," Rolfs said.

He said obesity has been examined as a risk factor in other parts of the country, "and it's not convincing. We usually do this type of thing (analysis of risk) through (academic) peer review. We're just not at that point yet. But it definitely looks suspicious to me."

e-mail: carrie@desnews.com