Risk factors and characteristics of patients with hospital-acquired influenza A: A Matched Case-Control Study

Abstract Background: Nosocomial influenza A brings hospitalized patients additional cost of care and considerable mortality, but predictors for hospital-acquired influenza A at the early stage remained unidentified. We aimed to describe the characteristics of patients vulnerable for hospital-acquired influenza A and identify its risk factors, which would help clinicians control nosocomial infection and ease the burden of treatment. Methods: A case-control study was conducted in hospitalized patients aged ≥ 18 years in a level A tertiary teaching hospital during the 2018-2019 influenza A season. Information of patients was retrieved from hospital-based medical records system. Hospital-acquired influenza A was defined as cases diagnosed 7 days or more after admission, who had no signs of viral respiratory infection on admission. The controls with no influenza infection were selected by the following criterion. Namely, patients were exposed to the same setting in the same period of time. We identified risk factors using conditional logistic regression and described characteristics of hospital-acquired influenza A through comparing the clinical data between influenza infected patients and controls. Results: Of 412 hospitalized patients with influenza A from all departments of the investigated hospital, 93 (22.6%) cases were classified as hospital-acquired influenza A. Older age (>65 years old) accounted for 34.4%. Hypertension (41.9%), coronary heart disease (21.5%) and cerebrovascular disease (20.4%) were the most common comorbidities. Before the infection 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 matched controls. Notably, infected patients had a longer hospital stay [18(12-27.5) days VS 14(11-20) days, P=0.002], and higher mortality (10.8% VS 2.2%, P=0.017 ). Lymphocytopenia (OR: 3.107; 95% CI 1.238-7.796; P =0.016), hypoalbuminemia (OR: 2.241; 95% CI 1.099-4.570; P =0.027) and pleural effusion (OR: 3.094; 95% CI 1.263-7.583; P =0.014) were independently associated with hospital-acquired influenza A. Conclusions: Lymphocytopenia, hypoalbuminemia and pleural effusion were independent risk factors that could help identify patients at high risk of hospital-acquired influenza A, which extended hospital stay and was associated with high mortality.