Sociodemographic Factors and Clinical Conditions Associated to Hospitalization in Influenza A (H1N1) 2009 Virus Infected Patients in Spain, 2009–2010

Abstract

The emergence and pandemic spread of a new strain of influenza A (H1N1) virus in 2009 resulted in a serious alarm in clinical and public health services all over the world. One distinguishing feature of this new influenza pandemic was the different profile of hospitalized patients compared to those from traditional seasonal influenza infections. Our goal was to analyze sociodemographic and clinical factors associated to hospitalization following infection by influenza A(H1N1) virus. We report the results of a Spanish nationwide study with laboratory confirmed infection by the new pandemic virus in a case-control design based on hospitalized patients. The main risk factors for hospitalization of influenza A (H1N1) 2009 were determined to be obesity (BMI≥40, with an odds-ratio [OR] 14.27), hematological neoplasia (OR 10.71), chronic heart disease, COPD (OR 5.16) and neurological disease, among the clinical conditions, whereas low education level and some ethnic backgrounds (Gypsies and Amerinds) were the sociodemographic variables found associated to hospitalization. The presence of any clinical condition of moderate risk almost triples the risk of hospitalization (OR 2.88) and high risk conditions raise this value markedly (OR 6.43). The risk of hospitalization increased proportionally when for two (OR 2.08) or for three or more (OR 4.86) risk factors were simultaneously present in the same patient. These findings should be considered when a new influenza virus appears in the human population.

Risk factors associated with hospitalisation for influenza-associated severe acute respiratory illness in South Africa: A case-population study

“…Other studies have also identified smoking as a risk factor for increased influenza severity [30] but many were not statistically significant after adjusting for confounders [27,31]. Our findings could be explained by the fact that most of the SARI patients are female, who are more likely to be HIV-infected, and patients may quit smoking once sick, prior to hospital admission.…”

“…In contrast to HIV non-endemic countries like United States [26] and Spain [27], HIV has been implicated as a risk factor for influenza hospitalisation and severe disease in highly endemic settings like South Africa [5] and Kenya [28]. Cohen et al demonstrated that HIV-infected patients had a 4–8 times greater hospitalisation incidence, longer inpatient hospital admission by 2–7 days and more deaths when compared to HIV-uninfected patients [5].…”

Pregnancy as a risk factor for severe outcomes from influenza virus infection: A systematic review and meta-analysis of observational studies

“…A potential explanation for the high heterogeneity between these two studies was related to the inclusion criteria: while one study included patients presenting to the emergency department in Turkey [14], the other study included a mix of patients from a hospital emergency department and from outpatient clinics in Canada [8]. The three studies that reported risk estimates adjusted for other co-morbidities, all found slightly higher risks associated with pregnancy in the adjusted versus unadjusted analysis [8], [9], [10].…”

Social class based on occupation is associated with hospitalization for A(H1N1)pdm09 infection. Comparison between hospitalized and ambulatory cases

“…Following this argument, it is possible that occupation classification might differentiate between groups of individuals with similar clinical and behavioural risk factors of influenza infection, by severity of A (H1N1)pdm09 influenza infection and also to differentiate them according to utilization of health services [15].…”