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Increasing laboratory confirmed cases of influenza in Europe, particularly cases of influenza B in the south west

John Paget (j.paget@nivel.nl), EISS co-ordination centre, Utrecht, the Netherlands, on behalf of EISS.

Eleven networks in Europe reported no influenza activity to the European Influenza Surveillance Scheme (EISS, http://www.eiss.org/) in the week ending 29 December 2002 (week 52). Four networks reported sporadic activity (Belgium, Portugal, Spain and Switzerland), and one network (France) reported regional activity (1). A report of no influenza activity indicates that the overall level of clinical activity was at baseline levels. In France, influenza activity was the highest in the Rhône-Alpes (south east), the Midi-Pyrénées (south west) and the Normandy (north west) regions. The intensity of clinical activity was medium in Spain and low in all of the other networks.

A total of 3604 sentinel respiratory specimens have been tested for influenza since 30 September 2002. Of these, 109 (3%) have tested positive for influenza A or B. Influenza B was the dominant strain, accounting for 77% of the positive specimens. Twenty three percent were found to be influenza A (see figure). EISS has received no reports this season of the influenza A(H1N2) virus strain that circulated in Europe last season (mainly in England and Ireland) (2). Most of the cases of influenza B (86%) reported so far this season, have been reported by Spain (29), France (26) and Portugal (18).

Figure. Sentinel respiratory specimens reported to EISS, end of September to end of December 2002 (30/9/2002 – 29/12/2002). n=109.

Influenza B infections have been the dominant influenza type in Portugal and Spain in recent weeks. They have also been the most frequent in France, but are co-circulating with influenza A viruses. Interestingly, in week 52/2002 the dominant virus in the Rhône-Alpes region was influenza B, whereas in the Midi-Pyrénées it was influenza A(H1) (not yet fully characterised) and in Normandy influenza B was co-circulating with influenza A(H3N2).

All of the influenza viruses detected/isolated so far this season by EISS have been closely related to the 2002-03 influenza vaccine strains.

The total number of respiratory specimens collected by sentinel physicians in week 52/2002 was 161 (compared to 305 in week 51/2002); 100 (62%) of these were collected in France. The low numbers of specimens collected is a reflection of the holiday period. The percentage of sentinel specimens that tested positive for influenza (A or B) was 5.6%, ranging from 0% in most networks to 8% in France.

The surveillance of influenza in week 52/2002 was affected by the Christmas/New Year holidays. The clinical and virological data are sent with a delay and/or processed more slowly than usual and the EISS database is not yet complete. These factors can affect the apparent clinical morbidity rates in some countries, and the data for week 52/2002 should therefore be interpreted with caution.

EISS aims to contribute to a reduction in morbidity and mortality associated with influenza in Europe. One of the ways it does this is by publishing a Weekly Electronic Bulletin on influenza activity in Europe. This bulletin describes the epidemiological and virological spread of influenza in the 19 countries (22 surveillance networks) that are members of EISS. During the current influenza season, EISS includes 28 national reference laboratories, at least 10,600 sentinel physicians and covers a total population of 441 million inhabitants.