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Comparative Study
. 2010 Dec 15;51(12):1362-9.
doi: 10.1086/657314. Epub 2010 Nov 11.

Elevated influenza-related excess mortality in South African elderly individuals, 1998-2005

Cheryl Cohen  1 , Lone Simonsen, Jong-Won Kang, Mark Miller, Jo McAnerney, Lucille Blumberg, Barry Schoub, Shabir A Madhi, Cécile Viboud
Affiliations
Comparative Study

Elevated influenza-related excess mortality in South African elderly individuals, 1998-2005

Cheryl Cohen et al. Clin Infect Dis. .

Abstract

Background: Although essential to guide control measures, published estimates of influenza-related seasonal mortality for low- and middle-income countries are few. We aimed to compare influenza-related mortality among individuals aged ≥65 years in South Africa and the United States.

Methods: We estimated influenza-related excess mortality due to all causes, pneumonia and influenza, and other influenza-associated diagnoses from monthly age-specific mortality data for 1998-2005 using a Serfling regression model. We controlled for between-country differences in population age structure and nondemographic factors (baseline mortality and coding practices) by generating age-standardized estimates and by estimating the percentage excess mortality attributable to influenza.

Results: Age-standardized excess mortality rates were higher in South Africa than in the United States: 545 versus 133 deaths per 100,000 population for all causes (P<.001) and 63 vs 21 deaths per 100,000 population for pneumonia and influenza (P=.03). Standardization for nondemographic factors decreased but did not eliminate between-country differences; for example, the mean percentage of winter deaths attributable to influenza was 16% in South Africa and 6% in the United States (P<.001). For all respiratory causes, cerebrovascular disease, and diabetes, age-standardized excess death rates were 4-8-fold greater in South Africa than in the United States, and the percentage increase in winter deaths attributable to influenza was 2-4-fold higher.

Conclusions: These data suggest that the impact of seasonal influenza on mortality among elderly individuals may be substantially higher in an African setting, compared with in the United States, and highlight the potential for influenza vaccination programs to decrease mortality.

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Figures

Figure 1
Figure 1
Observed and predicted (baseline) deaths in persons aged ⩾65 years, 1998–2005, South Africa. A, Reported influenza deaths, predicted deaths, epidemic threshold (upper 95% confidence interval of predicted deaths), and number of influenza viral isolations (all ages) by month. B, Deaths due to pneumonia and influenza (P&I). C, Deaths due to all causes. Note that the number of deaths predicted is under the assumption that influenza viruses were not circulating.
Table 1
Table 1
Comparison of Causes of Death in Persons Aged ⩾65 Years in South Africa and the United States, Based on All Deaths Occurring during 1998–2005
Table 2
Table 2
Annual Excess Deaths due to Pneumonia and Influenza (P&I) and All Causes in Individuals Aged ⩾65 Years, South Africa, 1998–2005
Table 3
Table 3
Comparison of Mean Seasonal Estimates of Influenza-Related Excess Mortality in Individuals Aged ⩾65 Years in South Africa (SA) for 1998–2005 and in the United States (US) for the 1997/1998 to 2004/2005 Seasons
Table 4
Table 4
Age-Specific Estimates of Influenza-Related Excess Mortality Rates per 100,000 Population Aged ⩾65 Years in South Africa (SA) and the United States (US)
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References

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