Risk factors for hospital-acquired influenza A and patient characteristics: a matched case-control study

BackgroundWhile hospital-acquired influenza A results in an additional cost burden and considerable mortality in patients, its risk factors are unknown. We aimed to describe the characteristics of patients vulnerable to hospital-acquired influenza A and to identify its risk factors to assist clinicians control hospital-acquired infections and reduce the burden of treatment.MethodsA case-control study was conducted among hospitalized patients aged >= 18years at a tertiary level teaching hospital during the 2018-2019 influenza A season. Patient data were retrieved from hospital-based electronic medical records. Hospital-acquired influenza A was defined as a case of influenza A diagnosed 7days or more after admission, in a patient with no evidence of influenza A infection on admission. The controls without influenza A were selected among patients exposed to the same setting and time period. We identified risk factors using conditional logistic regression and described the characteristics of hospital-acquired influenza A by comparing the clinical data of infected patients and the controls.ResultsOf the 412 hospitalized patients with influenza A from all the departments in the study hospital, 93 (22.6%) cases were classified as hospital-acquired. The most common comorbidities of the 93 cases were hypertension (41.9%), coronary heart disease (21.5%), and cerebrovascular disease (20.4%). Before the onset of hospital-acquired influenza A, patients presented more lymphocytopenia (51.6% vs 35.5%, P=0.027), hypoalbuminemia (78.5% vs 57.0%, P=0.002), and pleural effusion (26.9% vs 9.7%, P=0.002) than the matched controls. Infected patients also had longer hospital stays (18days vs 14days, P=0.002), and higher mortality rates (10.8% vs 2.2%, P=0.017) than the matched controls. Lymphocytopenia (odds ratio [OR]: 3.11; 95% confidence interval [CI]: 1.24-7.80; P=0.016), hypoalbuminemia (OR: 2.24; 95% CI: 1.10-4.57; P=0.027), and pleural effusion (OR: 3.09; 95% CI: 1.26-7.58; P=0.014) were independently associated with hospital-acquired influenza A.ConclusionsLymphocytopenia, hypoalbuminemia and pleural effusion are independent risk factors that can help identify patients at high risk of hospital-acquired influenza A, which can extend hospital stay and is associated with a high mortality.