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. 2018 May;12(3):360-373.
doi: 10.1111/irv.12529. Epub 2018 Feb 1.

The effects of the attributable fraction and the duration of symptoms on burden estimates of influenza-associated respiratory illnesses in a high HIV prevalence setting, South Africa, 2013-2015

Stefano Tempia  1   2   3 , Sibongile Walaza  3   4 , Jocelyn Moyes  3   4 , Adam L Cohen  1   5 , Claire von Mollendorf  3   4 , Meredith L McMorrow  1   2 , Sarona Mhlanga  3 , Florette K Treurnicht  3 , Marietjie Venter  6 , Marthi Pretorius  3   6   7 , Orienka Hellferscee  3   8 , Nicole Wolter  3   8 , Anne von Gottberg  3   8 , Arthemon Nguweneza  3 , Johanna M McAnerney  3 , Halima Dawood  9   10 , Ebrahim Variava  11   12   13 , Shabir A Madhi  3   14   15 , Cheryl Cohen  3   4
Affiliations

The effects of the attributable fraction and the duration of symptoms on burden estimates of influenza-associated respiratory illnesses in a high HIV prevalence setting, South Africa, 2013-2015

Stefano Tempia et al. Influenza Other Respir Viruses. 2018 May.

Abstract

Background: The attributable fraction of influenza virus detection to illness (INF-AF) and the duration of symptoms as a surveillance inclusion criterion could potentially have substantial effects on influenza disease burden estimates.

Methods: We estimated rates of influenza-associated influenza-like illness (ILI) and severe acute (SARI-10) or chronic (SCRI-10) respiratory illness (using a symptom duration cutoff of ≤10 days) among HIV-infected and HIV-uninfected patients attending 3 hospitals and 2 affiliated clinics in South Africa during 2013-2015. We calculated the unadjusted and INF-AF-adjusted rates and relative risk (RR) due to HIV infection. Rates were expressed per 100 000 population.

Results: The estimated mean annual unadjusted rates of influenza-associated illness were 1467.7, 50.3, and 27.4 among patients with ILI, SARI-10, and SCRI-10, respectively. After adjusting for the INF-AF, the percent reduction in the estimated rates was 8.9% (rate: 1336.9), 11.0% (rate: 44.8), and 16.3% (rate: 22.9) among patients with ILI, SARI-10, and SCRI-10, respectively. HIV-infected compared to HIV-uninfected individuals experienced a 2.3 (95% CI: 2.2-2.4)-, 9.7 (95% CI: 8.0-11.8)-, and 10.0 (95% CI: 7.9-12.7)-fold increased risk of influenza-associated illness among patients with ILI, SARI-10, and SCRI-10, respectively. Overall 34% of the estimated influenza-associated hospitalizations had symptom duration of >10 days; 8% and 44% among individuals aged <5 and ≥5 years, respectively.

Conclusion: The marginal differences between unadjusted and INF-AF-adjusted rates are unlikely to affect policies on prioritization of interventions. HIV-infected individuals experienced an increased risk of influenza-associated illness and may benefit more from annual influenza immunization. The use of a symptom duration cutoff of ≤10 days may underestimate influenza-associated disease burden, especially in older individuals.

Keywords: HIV; South Africa; attributable fraction; influenza; influenza-like illness; rates; severe respiratory illness; symptom duration.

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Figures

Figure 1
Figure 1
Weekly number of influenza‐positive specimens by type and subtype among outpatients with influenza‐like illness and inpatients with severe acute or chronic respiratory illness, Klerksdorp and Pietermaritzburg, South Africa, 2013‐2015
Figure 2
Figure 2
Overall unadjusted and attributable fraction‐adjusted mean annual influenza‐associated respiratory illness rates by age group, Klerksdorp and Pietermaritzburg, South Africa, 2013‐2015. (A) Influenza‐like illness; (B) severe acute respiratory illness (symptom duration ≤10 days); (C) severe chronic respiratory illness (symptom duration >10 days)
Figure 3
Figure 3
Proportion of attributable fraction‐adjusted influenza‐associated severe respiratory illness hospitalization rates by duration of symptoms, Klerksdorp and Pietermaritzburg, South Africa, 2013‐2015. (A) All; (B) HIV‐infected; (C) HIV‐uninfected
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