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

This study aimed to analyse the existence of an association between social class (categorized by type of occupation) and the occurrence of A(H1N1)pmd09 infection and hospitalization for two seasons (2009-2010 and 2010-2011). This multicentre study compared ambulatory A(H1N1)pmd09 confirmed cases with ambulatory controls to measure risk of infection, and with hospitalized A(H1N1)pmd09 confirmed cases to asses hospitalization risk. Study variables were: age, marital status, tobacco and alcohol use, pregnancy, chronic obstructive pulmonary disease, chronic respiratory failure, cardiovascular disease, diabetes, chronic liver disease, body mass index >40, systemic corticosteroid treatment and influenza vaccination status. Occupation was registered literally and coded into manual and non-manual worker occupational social class groups. A conditional logistic regression analysis was performed. There were 720 hospitalized cases, 996 ambulatory cases and 1062 ambulatory controls included in the study. No relationship between occupational social class and A(H1N1)pmd09 infection was found [adjusted odds ratio (aOR) 0·97, 95% confidence interval (CI) 0·74-1·27], but an association (aOR 1·53, 95% CI 1·01-2·31) between occupational class and hospitalization for A(H1N1)pmd09 was observed. Influenza vaccination was a protective factor for A(H1N1)pmd09 infection (aOR 0·41, 95% CI 0·23-0·73) but not for hospitalization. We conclude that manual workers have the highest risk of hospitalization when infected by influenza than other occupations but they do not have a different probability of being infected by influenza.

Score to identify the severity of adult patients with influenza A (H1N1) 2009 virus infection at hospital admission.

The objective of this paper was to develop a prognostic index for severe complications among hospitalized patients with influenza A (H1N1) 2009 virus infection. We conducted a prospective observational cohort study of 618 inpatients with 2009 H1N1 virus infection admitted to 36 Spanish hospitals between July 2009 and February 2010. Risk factors evaluated included host-related factors and clinical data at admission. We developed a composite index of severe in-hospital complications (SIHC), which included: mortality, mechanical ventilation, septic shock, acute respiratory distress syndrome, and requirement for resuscitation maneuvers. Six factors were independently associated with SIHC: age >45 years, male sex, number of comorbidities, pneumonia, dyspnea, and confusion. From the ß parameter obtained in the multivariate model, a weight was assigned to each factor to compute the individual influenza risk score. The score shows an area under the receiver operating characteristic (ROC) curve of 0.77. The SIHC rate was 1.9 % in the low-risk group, 10.3 % in the intermediate-risk group, and 29.6 % in the high-risk group. The odds ratio for complications was 21.8 for the high-risk group compared with the low-risk group. This easy-to-score influenza A (H1N1) 2009 virus infection risk index accurately stratifies patients hospitalized for H1N1 virus infection into low-, intermediate-, and high-risk groups for SIHC.