Differences in swine flu response by population

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Remember when there was talk about how SARS might disproportionately hit Chinese in comparison to other populations? Here’s a new paper on how Swine Flu may progress in different populations, Clinical Findings and Demographic Factors Associated With ICU Admission in Utah Due to Novel 2009 Influenza A(H1N1) Infection:

The ICU cohort of 47 influenza patients had a median age of 34 years, Acute Physiology and Chronic Health Evaluation II score of 21, and BMI of 35 kg/m2. Mortality was 17% (8/47). All eight deaths occurred among the 64% of patients (n = 30) with ARDS, 26 (87%) of whom also developed multiorgan failure. Compared with the Salt Lake County population, patients with novel A(H1N1) were more likely to be obese (22% vs 74%; P < .001), medically uninsured (14% vs 45%; P < .001), and Hispanic (13% vs 23%; P < .01) or Pacific Islander (1% vs 26%; P < .001). Observed ICU admissions were 15-fold greater than expected for those with BMI ≥ 40 kg/m2 (standardized morbidity ratio 15.8, 95% CI, 8.3-23.4) and 1.5-fold greater than expected among those with BMI of 30 to 39 kg/m2 for age-adjusted and sex-adjusted rates for Salt Lake County.

Remember that these are 47 intensive care patients, the most extreme cases. Here’s a table with N’s & odds ratios:

I’m struck by the Pacific Islander results. Obviously there are some confounds here, Pacific Islanders are heavier and have lower socioeconomic status from what I know. But the odds ratio is so high. Unfortunately I don’t see the obesity levels of the Pacific Islanders broken out, rather, they controlled for ethnicity by looking only at the white population (and obesity, smoking, etc., still mattered). I wonder how much more susceptible groups from low density or isolated societies, like Pacific Islanders, are to endemic infectious diseases.

Citation: doi: 10.1378/chest.09-2517, CHEST April 2010 vol. 137 no. 4 752-758

3 Comments

  1. Mortality during the ‘Spanish flu’ outbreak in Samoa following World War One was massive – over a quarter of the population died. This was before the wholesale importation of high-sugar and the export/dumping of high-fat low-cost cuts of meat into Polynesia (‘Lamb-flaps’ from New Zealand)led to a surge in obesity in Polynesian populations. The population at the time was relatively fit and healthy.
    Influenza mortality in the Maori population was also much higher than that of the European/Pakeha population (my husband is Maori and groups of adult’s graves in their family cemetery all with the year of death are a stark reminder of this).
    It may well be that the relatively low genetic diversity found in most Polynesian populations due to alleles being lost through a series of genetic bottlenecks/founder population events. The last island groups settled were the results of many sequential colonisation events. Recent genetic data suggests that New Zealand for example may have been settled by a population icluding less than 70 women.
    This may well be one of the answers pointing toward why the Pacific Islander ICU numbers far outweigh their percentages in the general population

  2. Apologies, Line six should read “all with the SAME year of death”

  3. Persons of aboriginal ancestry disproportionately suffered from H1N1.

    http://www.cmaj.ca/cgi/content/short/182/3/257?rss=1

    Maybe persons directly descended from hunter-gatherers have less resistance to influenza. Likely it is a disease that began to infect humans after the development of agriculture, since it comes from birds and pigs.

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