HEALTH NEWS

Study Title:

Preliminary Analysis of Swine Flu Deaths

Study Abstract

This article describes the characteristics of 574 deaths associated with pandemic H1N1 influenza up to 16 July 2009. Data (except from Canada and Australia) suggest that the elderly may to some extent be protected from infection. There was underlying disease in at least half of the fatal cases. Two risk factors seem of particular importance: pregnancy and metabolic condition (including obesity which has not been considered as risk factor in previous pandemics or seasonal influenza).

Introduction

To date, there are few data on risk factors, severe cases and deaths associated with pandemic H1N1 influenza 2009. Estimating and interpreting case fatality ratios (CFR) is difficult, mainly due to the challenge of accurately estimating the numerator (N deaths) and the denominator (N cases) [1], especially during a pandemic that is still evolving. Furthermore, many countries have abandoned individual case counts and systematic screening of all suspect cases. This article aims to describe the characteristics of reported deaths, to assess the CFR and high-risk profiles linked with underlying disease, while assessing possible bias.

Methods

The study is based on an analysis of available data until 16 July 2009, as compiled by the epidemic intelligence team at the French institute for public health surveillance (Institut de Veille Sanitaire, InVS), using a well-defined methodology [2]. The individual or aggregated data originated from validated official sources (Ministries of Health, local or national public health authorities, European Centre for Disease Prevention and Control, United States Centers for Disease Control and Prevention, World Health Organization), completed by informal sources when needed.

Results

The first (retrospectively) confirmed death occurred in Oaxaca State, Mexico, (onset of symptoms on 4 April 2009). As of 16 July 2009, InVS was aware of 684 confirmed deaths reported worldwide since the start of the pandemic (Figure 1) for a total of 126,168 reported cases (Figure 2). At this stage, no deaths had been reported and scarce data was available from African countries.

Data were available for 574 deaths associated with pandemic H1N1 influenza 2009: individual data for 449 cases in 26 countries (Table 1, Figure 2) and aggregated data for 125 cases in Mexico [3].

The quality and completeness of the data regarding age, sex, date of death and the notion of underlying disease varied greatly for each case. The overall 'computed CFR' (number of reported deaths per number of reported cases as of 16 July 2009) was 0.6% and varied from 0.1% to 5.1% depending on the country (and the accurate quantification of deaths and overall case counts) (Table 1).

Deaths by sex and age

Data on sex were available for 503 fatal cases worldwide (257 men and 246 women, sex ratio=1.04). Data on age were available for 468 fatal cases worldwide (343 with individual data and 125 with aggregated data). Data on both information (age and sex) were available for 448 fatal cases (Figure 3).

Although previous reports suggested that cases of pandemic H1N1 influenza 2009 occurred mainly in children [4], the mean and median age of the 343 fatal cases in our analysis were 37 years (range 0-85 years). Most deaths (51%) occurred in the age group of 20-49 year-olds, but there was considerable variation depending on country or continent (Table 2). Overall, 12% of deaths occurred in cases aged 60 years or more, but 36% of reported deaths in Canada (mainly female) and 28% in Australia occurred in this age group.

Study Information

L Vaillant, G La Ruche, A Tarantola, P Barboza.
Epidemiology of fatal cases associated with pandemic H1N1 influenza 2009
Eurosurveillance
2009 August
French Institute for Public Health Surveillance (Institut de Veille Sanitaire, InVS), St Maurice, France.