TORONTO — 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.
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.
The damage to lung tissue is consistent with that inflicted by ARDS or acute respiratory distress symptom, Zaki says, referring to an often-fatal syndrome.
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 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 have died suffered lung damage that would have made it difficult to deliver enough oxygen into their bloodstreams, Zaki says.
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 Hebert, 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.
Doctors 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.”
Roughly 90 per cent of the cases studied had underlying medical conditions.
A separate report issued by the CDC on Thursday revealed that 67 per cent of the 36 American children who died from swine flu had at least one high risk medical condition.
“(Extreme) obesity was the top one and then hypertension or chronic cardiac conditions, asthma — those were the top three,” Dr. Dianna Blau, who works with Zaki, says of the adult cases.
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.
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.
The report on deaths in children revealed there were also significant rates of bacterial co-infections among the children who died of swine flu. It said doctors should be aware of the potential and treat children with antibiotics if co-infections are found.
“When you get the flu, your immune system can be a little weakened, you can be more susceptible to other infections,” CDC director Dr. Thomas Frieden said Thursday during a media briefing.
“That’s an important message for doctors to know that if someone has the flu, they get better, then they get worse again with high fever, that’s a clue that maybe they should be treated with antibiotics.”