| Introduction
The circulation of influenza virus is associated with increased consultation
rates with general practitioners (GPs) (1), increased hospital admissions
(2), and excess deaths (3) and has to be considered in health care planning.
In western Europe, influenza viruses normally circulate in the winter
months, usually between October and March. During this season, surveillance
of clinical respiratory illness is intensified in several European countries.
Several indicators can be used to assess the impact of influenza epidemics.
These include mortality registration, outbreak investigations, acute admissions
to hospital, continuous reporting of morbidity by sentinel physicians,
and analyses of virus isolations. Within each European country some or
all of these indicators are used to greater or lesser extents to help
define the impact of influenza epidemics and to provide an early warning
system.
One of the first manifestations of influenza activity is an increase
in consultations by patients with GPs. Sentinel networks of physicians
have been set up in several countries, which monitor morbidity continuously
in defined populations. Linking data from clinical consultations for influenza-like
illness or acute respiratory illness with virological sampling from the
same population, usually by taking a combined nose and throat swab from
cases, improves the specificity of detection of influenza, and allows
the impact of influenza in defined communities to be assessed.
The European Influenza Surveillance Scheme (EISS) is made up of sentinel
physician networks in nine European countries - Belgium, the Czech Republic,
England and Wales, France, Germany, Netherlands, Portugal, Scotland, Spain,
and Switzerland - and their corresponding national virology laboratories,
many of whom form part of the World Health Organization (WHO) global influenza
surveillance network. The objective of EISS is to collect linked clinical
virological data from each country via the Internet into a single database
(http://www.eiss.org), which is available for consultation by each of
the member states. Access to most of EISS database on the Internet is
password protected and is therefore accessible only to authorised institutions.
There is a public section of the database which includes map details of
the current influenza situation in Europe.
Methods
Each week participating countries report the number of consultations
for influenza-like illness and acute respiratory illness, a denominator
for the sentinel network (number of GPs or population size), the number
of cases sampled, and the number of influenza viruses detected by various
virological tests. Data are sent as they become available. Clinical and
virological data are reported by age and sex, usually within seven days
of the end of the recording week. The virological data include the numbers
of specimens submitted and the results of tests undertaken. Password restricted
access and validation procedures provide the necessary quality assurance.
Clinical data are updated for two weeks and virological data for six weeks
after the end of the recording week.
Results
The EISS database can be used to build up a current picture of the clinical
impact of influenza in Europe in the winter of 1997/98. At the time of
writing this article (week 04/98) data from eight European countries had
been deposited from week 40/97 to week 02/98 or week 03/98 in some cases.
Figure 1 shows that in no European country within the EISS have consultations
for influenza-like illness or acute respiratory illness risen above their
national threshold levels, but sporadic isolations of influenza viruses
of various types and subtypes have been made in several European countries.
The first detection of influenza virus in sentinel GP samples this season
in Europe occurred in Belgium with the detection of influenza B in week
41/97, followed by the detection of influenza A in week 42/97 in France
and Portugal, in week 45/97 in England, and sporadically in a number of
other countries subsequently (figure 1). The influenza A H1N1 and influenza
B viruses detected so far have been related to A/Bayern/7/95 and B/Harbin/7/94,
respectively, the vaccine strains for 1997/98. The influenza A H3N2 strains
characterised so far are related to A/Wuhan/359/95, the vaccine strain
for 1997/98, and a new drift variant A/Sydney/5/97.
Figure 1
|