Strikingly high levels of H1N1 virus were spotted in the lungs of people who died rapidly from swine flu. (C. S. Goldsmith and A. Balish/Centers for Disease Control/Reuters)

The lungs of people who have died from swine flu look more like those of the victims of H5N1 avian influenza than those of people who succumb to regular flu, the chief of infectious diseases pathology at the U.S. Centers for Disease Control says.

A study of about 70 fatal H1N1 cases so far also reveals there may be more incidences of co-infections with bacteria than was earlier thought, Dr. Sherif Zaki told The Canadian Press in an interview.

The damage to lung tissue is consistent with that inflicted by ARDS or acute respiratory distress symptom, Zaki says, referring to an often-fatal, difficult-to-treat syndrome that can have a number of causes. The U.S. National Heart, Lung and Blood Institute estimates about 30 per cent of people who develop ARDS die.

"In terms of the disease, yes, it [H1N1] is remarkably different than seasonal flu," Zaki says. "The pathology looks very similar to H5[N1]."

The dangerous H5N1 avian flu virus has killed 60 per cent of the 440 people known to have been infected with it. To date, though, the virus hasn't acquired the capacity to spread easily from person to person.

The swine flu patients who went on to die suffered lung damage and changes in the lungs that would have made it difficult to deliver enough oxygen into their bloodstreams, Zaki says.

ICU doctors struggle

That reflects the observation of intensive care doctors who've struggled to save these profoundly ill patients.

"That's what they saw in Winnipeg," Dr. Paul Hébert, an intensive care physician and editor of the Canadian Medical Association Journal, said recently of how hard it is to oxygenate swine flu patients who become gravely ill.

"They have everybody on experimental ventilators and techniques. They can barely keep them alive."

A number of doctors who have treated novel H1N1 patients — and colleagues who haven't yet — were meeting in Winnipeg this week discussing what steps hospitals and ICUs need to take to get ready for an expected increase in pandemic flu cases this fall and winter.

Zaki says finding ways to prevent cases from progressing to severe illness should be the goal, "because once it happens in these patients … it's very difficult to treat."

Underlying medical conditions common

Roughly 90 per cent of the cases studied had underlying medical conditions.

"[Extreme] obesity was the top one and then hypertension or chronic cardiac conditions, asthma — those were the top three," says Dr. Dianna Blau, who works with Zaki.

Others included diabetes and immune deficiencies.

Zaki says doctors treating people with these kinds of conditions should let their patients know so that they respond quickly if they catch the virus and start to get really sick.

Strikingly high levels of virus were spotted in the lungs of people who died rapidly from swine flu, he says, though less is seen in those who die after a longer battle with the virus.

"Some people die very quickly of it, within days. And some have more protracted illness, maybe two, three weeks," he says. "It's surprising the amounts [of virus] that you see …. But it's not unheard of," he adds, pointing to what was seen with SARS.

Earlier studies conducted in tissue culture and in ferrets — the best animal model for human flu — found the new virus is drawn to tissue found deep in the lung. That's a penchant it shares with H5N1. Seasonal flu viruses attack the upper airways.

Staph, strep co-infections

Zaki says about a third of the fatal cases his team has reviewed involved co-infection with a bacterium, though the culprit varies.

Sometimes it is Staphylococcus aureus — the drug-resistant kind, known by the nickname MRSA and antibiotic-sensitive varieties as well. Some cases have involved group A Streptococcus. And some have been co-infection with Streptococcus pneumoniae.

"Those are the main three that we found."

"It was not very clear initially," Zaki adds of the frequency with which co-infection seems to occur in these cases. "But the more we studied, the more we realized that these do happen."

He suggests pneumococcal vaccine, used in the elderly to lower the risk of pneumonia, could be a useful tool if given to younger people with underlying medical conditions. The highest numbers of deaths so far have been in people in their late 30s and 40s.

On Thursday, Dr. Thomas Friedman, director of the U.S. Centers for Disease Control and Prevention, also recommended pneumococcal vaccination for children and the elderly to prevent complications from H1N1.

Some of the cases of co-infection have been in people who were hospitalized for an extended period, which wouldn't be all that surprising. But some were seen in people who weren't hospitalized.

With the new virus causing severe disease in only a small portion of cases, public health authorities have been criticized for overreacting and overhyping the threat swine flu poses. Some critics have suggested the new flu isn't really much worse than seasonal influenza.

From Zaki's vantage point, however, this is not regular flu.

"This is a new virus. It causes a different disease than what we're used to," he says. "So I don't think anybody can predict exactly, but it would be foolish not to be trying to study the disease more."