# Clinical predictors of severe forms of influenza A(H1N1)pdm09 in adults and children during the 2009 epidemic in Brazil

## TL;DR

This study identifies clinical predictors of severe influenza A(H1N1)pdm09 in Brazil during 2009 and develops prediction models for adults and children.

## Contribution

The paper introduces three clinical prediction models for severe influenza based on epidemiological data from Brazil's 2009 epidemic.

## Key findings

- Systolic blood pressure, respiratory rate, dehydration, obesity, pregnancy, and vomiting were key predictors of severe influenza.
- Three prediction models showed good performance with ROC AUC values of 0.89, 0.98, and 0.91 for adults, adult women, and children.
- The study included 1653 participants with a mean age of 26, mostly female and with low education levels.

## Abstract

The World Health Organization (WHO) raised the global alert level for the A(H1N1) influenza pandemic in June 2009. However, since the beginning of the epidemic, the fight against the epidemic lacked foundations for managing cases to reduce the disease lethality. It was urgent to carry out studies that would indicate a model for predicting severe forms of influenza. This study aimed to identify risk factors for severe forms during the 2009 influenza epidemic and develop a prediction model based on clinical epidemiological data. A case-control of cases notified to the health secretariats of the states of Rio de Janeiro, São Paulo, Minas Gerais, Paraná, and Rio Grande do Sul was conducted. Cases had fever, respiratory symptoms, positive confirmatory test for the presence of the virus associated with one of the three conditions: (i) presenting respiratory complications such as pneumonia, ventilatory failure, severe acute respiratory distress syndrome, sepsis, acute cardiovascular complications or death; or respiratory failure requiring invasive or non-invasive ventilatory support, (ii) having been hospitalized or (iii) having been admitted to an Intensive Care Unit. Controls were individuals diagnosed with the disease on the same date (or same week) as the cases. A total of 1653 individuals were included in the study, (858 cases/795 controls). These participants had a mean age of 26 years, a low level of education, and were mostly female. The most important predictors identified were systolic blood pressure in mmHg, respiratory rate in bpm, dehydration, obesity, pregnancy (in women), and vomiting (in children). Three clinical prediction models of severity were developed, for adults, adult women, and for children. The performance evaluation of these models indicated good predictive capacity. The area values under the ROC curve of these models were 0.89; 0.98 and 0.91 respectively for the model of adults, adult women, and children respectively.