Complicated hospitalization due to influenza: results from the Global Hospital Influenza Network for the 2017-2018 season

Abstract

Background: Since 2011, the Global Influenza Hospital Surveillance Network (GIHSN) has used active surveillance to prospectively collect epidemiological and virological data on patients hospitalized with influenza virus infection. Here, we describe influenza virus strain circulation in the GIHSN participant countries during 2017-2018 season and examine factors associated with complicated hospitalization among patients admitted with laboratory-confirmed influenza illness.

Methods: The study enrolled patients who were hospitalized in a GIHSN hospital in the previous 48 h with acute respiratory symptoms and who had symptoms consistent with influenza within the 7 days before admission. Enrolled patients were tested by reverse transcription-polymerase chain reaction to confirm influenza virus infection. "Complicated hospitalization" was defined as a need for mechanical ventilation, admission to an intensive care unit, or in-hospital death. In each of four age strata (< 15, 15-< 50, 50-< 65, and ≥ 65 years), factors associated with complicated hospitalization in influenza-positive patients were identified by mixed effects logistic regression and those associated with length of hospital stay using a linear mixed-effects regression model.

Results: The study included 12,803 hospitalized patients at 14 coordinating sites in 13 countries, of which 4306 (34%) tested positive for influenza. Influenza viruses B/Yamagata, A/H3N2, and A/H1N1pdm09 strains dominated and cocirculated, although the dominant strains varied between sites. Complicated hospitalization occurred in 10.6% of influenza-positive patients. Factors associated with complicated hospitalization in influenza-positive patients included chronic obstructive pulmonary disease (15-< 50 years and ≥ 65 years), diabetes (15-< 50 years), male sex (50-< 65 years), hospitalization during the last 12 months (50-< 65 years), and current smoking (≥65 years). Chronic obstructive pulmonary disease (50-< 65 years), other chronic conditions (15-< 50 years), influenza A (50-< 65 years), and hospitalization during the last 12 months (< 15 years) were associated with a longer hospital stay. The proportion of patients with complicated influenza did not differ between influenza A and B.

Conclusions: Complicated hospitalizations occurred in over 10% of patients hospitalized with influenza virus infection. Factors commonly associated with complicated or longer hospitalization differed by age group but commonly included chronic obstructive pulmonary disease, diabetes, and hospitalization during the last 12 months.

Keywords: Epidemiology; Hospitalization; Influenza; Mortality; Risk factors.

Fig. 1

Disposition and influenza positivity of included patients. Community-dwelling patients residing in predefined catchment areas of the participating hospitals and hospitalized < 48 h with presenting complaints potentially associated with influenza were eligible. Patients aged > 5 years had to have ≥1 systemic symptom (fever/feverishness, malaise, headache, or myalgia) and ≥ 1 respiratory symptom (cough, sore throat, or shortness of breath) and had to have been hospitalized < 7 days of the onset of the symptoms. Patients aged ≤5 years had to be hospitalized < 7 days after the appearance of symptoms potentially associated with influenza. Patients were excluded if they had been discharged from a hospital < 30 days before the current episode. Influenza infection was confirmed and typed/subtyped by RT-PCR

Fig. 2

Influenza strain circulation by year-week and World Health Organization influenza transmission zone. Influenza strains were detected by RT-PCR. An individual patient could have been positive for more than one strain of influenza

Fig. 3

Influenza strain circulation by site and overall during 2017–2018. Influenza strains were detected by RT-PCR. An individual patient could have been positive for more than one strain of influenza

Fig. 4

Proportion of influenza-positive patients with complicated hospitalization by age group. Complicated hospitalization was defined as ICU admission, mechanical ventilation, or death

Fig. 5

Adjusted odds ratios for complicated hospitalization in influenza-positive patients. Adjusted odds ratios for complicated hospitalization were determined in influenza-positive patients aged < 15 years (N = 1309), 15 to < 65 years (N = 1193), and ≥ 65 years (N = 776) by mixed effects logistic regression adjusted for age and vaccination for influenza during the previous 12 months and with site as a random effect. Complicated hospitalization was defined as ICU admission, mechanical ventilation, or death. Abbreviations: COPD, chronic obstructive pulmonary disease; CVD, cardiovascular disease

Fig. 6

Mean length of hospital stay in influenza-positive patients. Abbreviation: CI, confidence interval

Fig. 7

Adjusted coefficients for long hospital stays in influenza-positive patients. Coefficient estimates for length of hospital stay were determined in influenza-positive patients aged < 15 years (N = 1306), 15 to < 65 years (N = 1189), and ≥ 65 years (N = 775) by linear mixed-effects regression model adjusted for age and vaccination status and with site as a random effect. The coefficient indicates the change in length of hospital stay in days when the indicated factor is changed by one unit (i.e. from yes to no). Abbreviations: COPD, chronic obstructive pulmonary disease; CVD, cardiovascular disease