Contribution to Leptospirosis survey
in France in 2002
In 2002, 5283 serological and 91 bacteriological analyses have been performed.
The number of observed cases is 365 in continental France (
Table 1). This total includes 4 cases detected by PCR only and corresponds to an incidence rate of 0.61/100000 (Table 2).In overseas France, the 288 diagnosed cases (
Table 1) represent a rather low number. As in 2001, there are many disparities according to the geographical area. Usually they are mostly due to local changing availability of diagnosis procedures. The higher incidence rates (quite inferior to those reported during the nineties) are reported in New Caledonia (30/100000), French Guyana and West Indies (17.8/100000), French Polynesia (12.5/100000) and finally La Reunion (7.2/100000) (Table 2).In continental France, the season distribution exhibits a maximum in October although the five last months of the year all get an increased number of cases as compared to the last year (
Table 1).
Epidemiological features
Three distinct cases definitions are used according to the considered area. The aim is to not take into account the residual low titers in serology, the frequency of which is quite different from an area to another one.
*1) In New Caledonia, the incidence is so high (often > 100/100000) that, if considered, the prevalence of residual low titers would lead to overestimation of the disease. Confirmed cases are defined as bacteriologically or PCR confirmed ones and/or seroconverted patients (four fold increase in titer). Probable cases correspond to 2).
*2) In high endemicity area (usually < 50/100000) such as La Reunion and French Polynesia, a so-called "clinical" cut off (1/400 or more in Micro Agglutination Test: MAT against any of the pathogenic antigens) is used in order to prevent overestimation due to residual titers.
*3) In low endemicity areas, a so-called "epidemiological" cut off of 1/100 is considered. Indeed the low residual titers prevalence is unsignificant and, in opposition, if used, the 1/400 cut off would lead to underestimation of many cases due to the chronologically non-optimal sampling. It would also be the case for early treated leptospiroses or those due to Grippotyphosa serogroups (often characterized by low titers). This definition is used in French West Indies, French Guyana and continental France.
In 2002, the number of cases in continental France (357 serological cases) is the highest of the five last years (
Table 1). Two third of the cases occurred during the 2nd semester. The maximum (62 cases) is recorded in October (Table 2).The usual foci still in front position are: Pays de Loire (1.21/100000), Poitou-Charentes (1.34) and mainly Franche-Comte (1.61) although this year 2002 Basse Normandie (1.48) is ahead of Poitou-Charentes and Champagne-Ardennes (0.97). In addition, unexpectedly Brittany (1.07) and Limousin (1.11) are among the regions where the incidence is above 1/100000.
Concerning serogroups, Grippotyphosa is as prevalent as Icterohaemorrhagiae (23% each). Grippotyphosa is for instance largely responsible for the increased number of cases recorded in Northern and Western parts of France because of autumn-winter recrudescence of Grippotyphosa transmission. Canicola increasing (
Table 1) is probably an artefact.Overseas, in Caribbean, there has been an unexpectedly higher number of cases in Guadeloupe (97 cases) (
Table 3) than in Martinique (61) (Table 4). French Guyana, as usual, records a low number (13) (Table 5). New Caledonia drastically decreased (51 cases) as well as Mayotte and La Reunion exhibits a usual score (51) in spite of a hurricane which usually leads to an increased incidence(Table 6). Tahiti stopped to perform MAT diagnosis 2 years ago which explains the rather low number of cases (15) (Table 7) registered in 2002. All these cases (both culture and serological ones) have been diagnosed in Paris. However locally as well in Paris an IgM ELISA is available which allowed a complementary and presumptive diagnosis. 39 such probable cases should therefore be added to the 15 confirmed ones. It is of value to notice that as usual, There is a delay between PCR (diagnosis (quite early) and serological one (delayed). For instance, in a almost sketchy way, in La Reunion this year the four Pcr diagnosed patients were seronegative although the 47 serologically diagnosed ones were PCR negative.On a global scale, we may notice a rather high incidence in Atlantic (French West Indies and continental France) contrasting with a decrease in Western Pacific and Indian Ocean as compared to previous years. Is it a consequence of "El Niño" phenomenon which has been markedly present in 2001-2002? It is a simple and speculative hypothesis. It only means that there is a parallelism between drought and reduced transmission of Leptospirosis.