[Molecular strain typing contribution to epidemiology of tuberculosis in Limousin (1998 to 2006)]

We conducted a molecular epidemiology of Mycobacterium tuberculosis in Limousin, a French area with a low incidence of tuberculosis (4.8/100,000 inhabitants in 2005) to define the molecular diversity and the pattern of transmission.

Two hundred and fifty-nine strains were isolated (each strain corresponds to one patient) from 1998 to 2006. Both spoligotyping and MIRU15 were chosen for our study because of their discriminatory power.

Only 165 medical records were available: 99M/66F, mean age 56.4 years (14-94), 32.7% foreign-born patients, 16.9% homeless or living in shelters, 21.8% of immunocompromised patients (three HIV positive), 14.5% of alcohol addicts. Pulmonary manifestations were predominant (81.8%) with 45.1% of positive smears. Two strains among the 259 presented a multidrug resistance. Spoligotyping identified 136/259 spoligotypes (110 unique, 26 clusters composed of two to 36 isolates); within these 26 clusters, ST53 (n=36) and ST50 (n=19) were the most frequent. Three major families were observed as follow: T1 (30%), Haarlem (30%) and LAM (20%). MIRU15 identified 28/36 isolates in the ST53 group and 14/19 in the ST50 group. Eleven clusters (32 strains) with identical ST-MIRU15 were obtained with a proved case of recent transmission. Alcohol dependence, immunosuppression and pulmonary infections seem to be involved in transmission factors.

M. tuberculosis strains isolated in Limousin are characterized by their high genetic diversity. The rate of recent transmission (8.1%) is low and therefore a reactivation process is predominant in this area.