*
Data by year of diagnosis
** Includes
retrospective reporting before 1997
*** AIDS
data by year of diagnosis, not adjusted for reporting delays
na : not available
Discussion
HIV infection reporting systems are an established part
of HIV surveillance in most countries in western Europe. In the three
countries that account for two thirds of the cumulative total of reported
AIDS cases, however, HIV reporting either began only recently (Spain,
1999) or has yet to be implemented at national level (France, Italy).
Differences exist in the organisation of reporting and in the type and
format of information collected. As with AIDS, reports of HIV infection
from clinicians provide detailed epidemiological and clinical information.
Since diagnosis of HIV infection is less concentrated in specialised
centres, HIV infection reporting by clinicians may be less complete than
AIDS reporting, for which 75% to 100% of cases are estimated to be
reported (3). For this reason, in most countries cases of HIV infection
are (also) reported from laboratories, which are usually few in number and
may provide a more exhaustive count of diagnosed cases (e.g., higher than
95% in Denmark (4))
The elimination of duplicate reports and the ability to
match reports of HIV infection with other data sets are essential
requirements of an effective HIV reporting system. This implies the
collection of personal information which, in turn, creates a potential
risk for breaches of confidentiality. Among the measures taken to ensure
data security, most western European countries exclude names from the
collected personal information in HIV reports. In the UK, the use of ‘soundex’
codes (based on the surname) and date of birth provides efficient
identification of duplicates and linkage with AIDS case reports (5). The
use of initials, date of birth, and sex in a simulation made on the
nominal AIDS data set in Spain resulted in a very low proportion of truly
new cases being erroneously classified as duplicates (0.1%) (I Noguer,
personal communication). When non nominal HIV reporting is implemented,
the efficiency of matching and removal of duplicates also depends on the
completeness of the identifying information collected (6), however, and on
the (increasing) size of data sets. Further evaluations of this issue are
needed in Europe.
Reporting of HIV infection must be interpreted with
caution, taking into account other available epidemiological data, because
these reports do not provide a direct measurement of the incidence or
prevalence of HIV infection. The proportion of HIV infected individuals
who are diagnosed and reported varies according to the phase of the
epidemic (4), HIV testing patterns (7), and characteristics of
surveillance systems. In countries where HIV infection reporting began
early, the cumulative number of HIV reports can provide a minimum estimate
of prevalence if mortality data are also available or can be estimated.
Numbers of cases of HIV infection reported in 1998 are higher than numbers
of AIDS reports. HIV reporting is helping to improve assessment of the
scale and extent of recent HIV transmission in the population. Annual
numbers of HIV infections reported in the 1990s were relatively stable in
some countries and decreased in others (not shown here) (8). The
comparison of HIV and AIDS reporting data suggests that the level of HIV
transmission has remained relatively stable in recent years and that the
sudden decline of AIDS incidence has been due mainly to the effect of
treatments. Overall, sexual transmission accounts for the vast majority of
reported HIV infections, but the countries with the largest numbers of HIV
infected IDUs are poorly represented in these data. HIV trends by
transmission group are difficult to interpret in some countries because
the proportion of cases with unknown mode of transmission is high and has
changed over time
Four countries (Belgium, Greece, Luxembourg, United
Kingdom) already provided to the European system complete individual data
on cases reported since 1997, which include clinical stage at diagnosis
(around 80% of cases reported in 1998 were diagnosed before AIDS), the
probable year of infection (estimated for around 10% of cases) and
follow-up information on AIDS and death. These data should contribute to a
better description of recent HIV transmission trends, of disease
progression and of care at the population level.
HIV reporting has been recently introduced, expanded,
or improved in most western European countries and further developments
are underway. In particular, new and planned systems in southern countries
should contribute to a more representative surveillance picture of the HIV
epidemic in Europe. The widespead participation in the European HIV
reporting system reflects strong motivation for the collaborative
development of this surveillance tool. The current momentum of change
should facilitate better standardisation of surveillance definitions and
practices, which remains a major challenge for international surveillance.
*
The European Centre for the
Epidemiological Monitoring of AIDS (EuroHIV) is supported by the European
Commission (contract VS/1999/5227 (99CVVF4-023))
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