J Korean Med Sci.  2023 Jun;38(25):e188. 10.3346/jkms.2023.38.e188.

All-Cause and Cause-Specific Mortality Attributable to Seasonal Influenza: A Nationwide Matched Cohort Study

• Jang H
• Cho J
• Cho SK
• Lee D
• Cho Si
• Koh SB
• Shin DC
• Kim C

• KMID: 2543979
• DOI: http://doi.org/10.3346/jkms.2023.38.e188

Abstract

Background
Although influenza poses substantial mortality burden, most studies have estimated excess mortality using time-aggregated data. Here, we estimated mortality risk and population attributable fraction (PAF) attributed to seasonal influenza using individual-level data from a nationwide matched cohort.
Methods
Individuals with influenza during four consecutive influenza seasons (2013–2017) (n = 5,497,812) and 1:4 age- and sex-matched individuals without influenza (n = 20,990,683) were identified from a national health insurance database. The endpoint was mortality within 30 days after influenza diagnosis. All-cause and cause-specific mortality risk ratios (RRs) attributed to influenza were estimated. Excess mortality, mortality RR, and PAF of mortality were determined, including for underlying disease subgroups.
Results
Excess mortality rate, mortality RR, and PAF of all-cause mortality were 49.5 per 100,000, 4.03 (95% confidence interval [CI], 3.63–4.48), and 5.6% (95% CI, 4.5–6.7%). Cause-specific mortality RR (12.85; 95% CI, 9.40–17.55) and PAF (20.7%; 95% CI, 13.2– 27.0%) were highest for respiratory diseases. In subgroup analysis according to underlying disorders, PAF of all-cause mortality was 5.9% (95% CI, 0.6–10.7%) for liver disease, 5.8% (95% CI, 2.9–8.5%) for respiratory disease, and 3.8% (95% CI, 1.4–6.1%) for cancer.
Conclusion
Individuals with influenza had a 4-fold higher mortality risk than individuals without influenza. Preventing seasonal influenza may lead to 5.6% and 20.7% reductions in all-cause and respiratory mortality, respectively. Individuals with respiratory disease, liver disease, and cancer may benefit from prioritization when establishing influenza prevention strategies.

Keyword

Influenza; Cause of Death; Comorbidity; Mortality; Korea

Figure

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  Fig. 1 Sampling process and examples of matched pairs. The 36th week to 35th week in the risk period is equivalent to 1 year in the 2013/2014 to 2016/2017 seasons.

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  Fig. 2 RRs of all-cause mortality in individuals with influenza. Estimates are crude RRs derived from conditional logistic regression models.CI = confidence interval, COPD = chronic obstructive pulmonary disease, RR = risk ratio.aSignificantly different from the reference group (sex: male; age group: ≤ 19 years; Charlson comorbidity index: 0-point group; CHA2DS2-VASc score: low-risk group; underlying disease: respiratory disease).

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