The authors were interested in estimating the burden of medically- and non-medically-attended influenza-associated illness in South Africa, in particular among patients with different clinical presentations (all-respiratory, all-circulatory and non-respiratory/non-circulatory) and levels of severity (mild, severe-non-fatal and fatal). The authors found that the estimated mean annual number of influenza-associated illness episodes was 10,737,847 (19.8% of 54,096,705 inhabitants). Of these episodes, 98.7%, 1.2% and 0.1% were mild, severe-non-fatal and fatal, respectively. 25.6% of the mild, 43.9% of the severe-non-fatal and 42.8% of the fatal episodes were medically-attended. Influenza-associated respiratory illness accounted for 99.2%, 65.5% and 33.7% of any mild, severe-non-fatal and fatal illnesses, respectively. The authors found that the ecological and case-based estimates of medically-attended influenza-associated respiratory illnesses were similar: mild 1,778.8 vs. 1,703.3, severe-non-fatal 88.6 vs. 75.3 and fatal 3.8 vs. 3.5, per 100,000. Therefore there is a significant burden of influenza-associated symptomatic illness, including severe-non-fatal and fatal illness, with a large proportion being non-medically-attended. Estimates that included only influenza-associated respiratory illness substantially underestimated influenza-associated severe-non-fatal and fatal illness.
Read more here