This surveillance system was provoked into existence by the
virtual non-functioning of the existing notification system in France.
In its 12 years, 330 000 separate episodes of communicable disease
from a selected list of eight rubrics have been reported. This gives an
average of one diagnosis a week from each of about 500 general
practitioners, a surprisingly low rate considering the conditions that
are reported. These are an interesting but curious mix, ranging from
specific (measles, mumps, chickenpox, and HIV tests) through broad
(male urethritis, acute viral hepatitis) to diffuse (acute diarrhoeas,
flu-like illness).
The strength of the system is undoubtedly in its technical
sophistication. The use of paper is (presumably) minimal or
non-existent. Thus the statistics, provided the sentinel general
practitioners report promptly, are right up to date, while the analysis
and feedback are not only virtually instantaneous but also make use of
modern statistical methods such as " kriging." Ease of access to the
system and feedback are enviable.
The system nevertheless remains a general practitioner based
sentinel system and is not a substitute for the existing notification
system in France. Diseases for which local or individual public health
action need to be taken- such as rabies, meningococcal meningitis, or
food poisoning- cannot adequately be covered by this or indeed any
other general practitioner sentinel system. Measles and mumps- two
diseases for which it has been most useful- will decrease in incidence
with increasing vaccine coverage and become no longer viable for
sentinel reporting. Moreover, even when the incidences of these
infections were high, the number of reported cases to the sentinel
system was fairly low- between 401 and 1558 cases annually between 1985
and 1990 for measles.( 1) Since the general
practitioners' list sizes and the age and sex distributions of their
patients were not known, cases were often reported as numbers per
general practitioner and it is not clear how age specific incidence
rates are calculated.
Including acute diarrhoeal disease in the system without
laboratory backup may be of limited value unless there is an acute and
overwhelming epidemic, which is uncommon and unlikely nowadays.
Flu-like illness without appropriate laboratory backup will act as an
effective early warning system for influenza, but several other
infections masquerade under the heading of " flu-like" and in recent
years have undoubtedly accounted for more illnesses than influenza
itself. It is a pity that much valuable epidemiological information
on this type of illness will have been lost because the organism or
organisms responsible were not known. The time and place maps of
flu-like illness produced by the system( 2) are
beautiful but can be something of a mystery without this information.
The HIV tests give a positivity rate. This may be difficult to
interpret in a sentinel system if the distribution of HIV infection and
AIDS varies considerably by geographical area, especially when the
system has a high turnover rate of general
practitioners.( 3) What would also need to be known
is the pattern of patients' access to their general practitioners, and
not only for HIV.
The system is strong on collection, analysis, and feedback, three
cornerstones of successful surveillance. The public will, however,
mainly depend on the interpretation of the data if the system is to be
of use to them. With as many as 25 000 different maps and 10 000
graphs to choose from, even the average epidemiologist may find the
system a daunting one and the dedicated researcher is the person most
likely to want access. I suspect that the " weekly updated
electronic report, written by epidemiologists in simple
words" will be all that most of the public will ever want to see.
King's College School of Medicine
and Dentistry,
London SE5 9PJ
Norman Noah,
professor of
epidemiology and public health
REFERENCES
1 Mary M, Garnerin P, Roure C, Villeminot S, Swartz
TA, Valleron A-J. Six years of public health surveillance of measles in
France. Int J Epidemiol 1992; 21 :163-8.
2 Carrat F, Valleron A-J. Epidemiologic mapping using the
" kriging" method. Application to an influenza-like illness epidemic
in France. Am J Epidemiol 1992; 135 :1293-300.
3 Garnerin P, Saidi Y, Valleron A-J. The French communicable
diseases computer network, a seven-year experiment. Ann NY Acad
Sci 1992; 670 :29-42.
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