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.
