H1N1 sent higher pro­por­tion of pa­tients to ICU than reg­u­lar flu: re­port


TORONTO — H1N1 in­fluenza landed a higher pro­por­tion of Cana­di­ans in ICUs and on ven­ti­la­tors, and at a much younger age on av­er­age, than sea­sonal flu does in a typ­i­cal year, says a re­port as­sess­ing the com­par­a­tive im­pact of the pan­demic virus.

The study by the Cana­dian In­sti­tute for Health In­for­ma­tion com­pared hos­pi­tal­iza­tion statis­tics for H1N1 pa­tients be­tween April and De­cem­ber to data for pa­tients with reg­u­lar flu dur­ing the 2007-2008 sea­son.

“Ini­tially there were clin­i­cal per­cep­tions of the pa­tients: they seemed younger, they seemed sicker,” co-au­thor Kath­leen Mor­ris said of the H1N1 pan­demic that be­gan last April.

“ What this does is take a look at all of the H1N1 pa­tients that were hos­pi­tal­ized in Canada and com­pare them to a full hos­pi­tal­iza­tion (sea­sonal) flu year, so right across the coun­try,” Mor­ris, head of emerg­ing is­sues at CIHI, said Thurs­day from Ottawa.

“So it gives us a clearer sense of A, whether those find­ings are con­firmed by the data, and B, what mag­ni­tude is the dif­fer­ence.”

She said re­searchers were sur­prised at how big some of the dif­fer­ences were.

“Peo­ple ad­mit­ted to hospi­tal with H1N1 were younger than what we’d come to ex­pect in a typ­i­cal flu year, and those who died were younger, too,” said Mor­ris.

The me­dian age for pa­tients hos­pi­tal­ized with H1N1 was 28, com­pared to 71 for peo­ple ad­mit­ted for sea­sonal in­fluenza or flure­lated pneu­mo­nia. Among those sent to the ICU, the me­dian age of H1N1 pa­tients was the mid-40s, while sea­sonal flu pa­tients in a typ­i­cal year had a me­dian age of 68.

There was a stag­ger­ing dif­fer­ence in the me­dian ages of those who died: the mid-50s for H1N1 and the mid-80s for those from com­pli­ca­tions of sea­sonal flu, the most com­mon of which is pneu­mo­nia.

“So that’s some­thing about the pa­tient that seems to be a bit dif­fer­ent,” Mor­ris said. “There’s also some­thing about the kinds of care they needed in hospi­tal that seemed to be dif­fer­ent.”

The re­searchers found that a higher pro­por­tion of pa­tients in hospi­tal for H1N1 were ad­mit­ted to an in­ten­sive care unit — al­most one in six com­pared with about one in 10 of those with sea­sonal flu or flu-re­lated pneu­mo­nia.

And when it came to the pro­por­tion of pa­tients who needed a ven­ti­la­tor to as­sist breath­ing, H1N1 pa­tients were more than twice as likely to re­quire the ma­chines.

“ We also know that H1N1 ap­pears to have had a greater im­pact on some sub­groups of the pop­u­la­tion — like preg­nant women — than what we’d ex­pected in a typ­i­cal year,” Mor­ris said.

The study found the pro­por­tion of preg­nant women hos­pi­tal­ized with H1N1 was higher than what would be ex­pected in a typ­i­cal flu year — 21 per cent ver­sus 13 per cent.

Four of the preg­nant women with H1N1 died, she said. “And when we looked in all of 2007-8, there were no deaths among women hos­pi­tal­ized with flu or pneu­mo­nia.”

Com­ment­ing on the study, Dr. Michael Gardam said that while there are no big sur­prises in the re­port, it pro­vides an­other per­spec­tive us­ing a dif­fer­ent set of data.

“Most peo­ple with it did have mild dis­ease, but it re­ally points out that ac­tu­ally there were a sub­stan­tial num­ber of peo­ple who were quite sick who ended up ven­ti­lated,” said Gardam, head of in­fec­tion preven­tion and con­trol for Toronto’s Uni­ver­sity Health Net­work.

“It just re­in­forces how lucky we were, that had this virus had a lit­tle bit more of the right stuff, we could have been in re­ally big trou­ble.”

Gardam be­lieves we’ve seen the end of the H1N1 in­fluenza pan­demic be­cause such a high pro­por­tion of Cana­di­ans has ei­ther been in­fected with the virus or been vac­ci­nated against it.

“It be­comes very dif­fi­cult for the virus to take off ... You’re still go­ing to get cases, but you’re not go­ing to get those big peaks like we had in the first and sec­ond wave be­cause there sim­ply is not enough fuel.”

Mor­ris said that while the CIHI study an­swers a lot of ques­tions about what hap­pened with H1N1, more re­search is needed to an­swer the why ques­tions, as in “ Why did it be­have the way it did?”

Peo­ple ad­mit­ted to hospi­tal with H1N1 were younger than what we’d come to ex­pect in a typ­i­cal flu year, and those who died were younger, too. Kath­leen Mor­ris, head of emerg­ing is­sues at CIHI

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