Three-year longitudinal study of genotypes of Mycobacterium tuberculosis isolates in Tuscany, Italy

Abstract

The genetic diversity of 829 strains of Mycobacterium tuberculosis isolated during a 3-year period in Tuscany, Italy, a country with a low prevalence of tuberculosis, from 480 Italian-born and 349 foreign-born patients was determined by spoligotyping. The predominant spoligotype families were T (30.2% of isolates), Haarlem (19.9%), and the Latino-American and Mediterranean family (LAM) (11.2%); the remaining isolates were distributed among the Beijing (6.5%), S (4.2%), East Africa-India (EAI) (3.0%), Bovis (2.3%), Central Asia (CAS) (2.1%), Africanum (1.3%), and X (1.2%) families or were undefined (2.7%) or orphan (14.1%) isolates. Isolates of the families T, Haarlem, Bovis, and X were distributed among Italian- and foreign-born patients almost proportionally to the patients' numbers. Isolates of the LAM family were prevalent in foreign-born people (13.5%, versus 9.6% in Italian-born patients). Isolates of the S family were found almost exclusively in Italian-born patients, while strains of families EAI and CAS were isolated almost exclusively from foreign-born patients; Africanum isolates were all from African-born patients. The isolates of the Beijing family showed a trend to a steady increase during the survey. The prevalence of Beijing strains was 11.7% among foreign-born people and 2.7% among Italian-born patients. The Beijing strains were typed by the standardized IS6110 restriction fragment length polymorphism assay, which yielded a total of 38 distinct IS6110 patterns; 21 isolates (39.6%) occurred in six distinct clusters; of these, three contained two isolates and the other three contained four, five and six isolates, thus demonstrating that Beijing strains caused several tuberculosis outbreaks in the region. These findings indicate that transmission of Beijing strains between immigrants and the autochthonous population has occurred frequently and suggests an ongoing active transmission of the Beijing genotype in the region.

FIG. 1.

IS6110 fingerprints of 53 clinical isolates of M. tuberculosis of the Beijing genotype isolated in Tuscany, Italy, during 2002 to 2004. The IS6110 RFLP patterns were compared, and the dendrogram was constructed by using the unweighted-pair group method using average linkages and the Dice coefficient with the Gelcompar 4.1 software package (Applied Maths, Kortrijk, Belgium). The scale on the upper left depicts similarity coefficients. Clustered identical isolates are highlighted in light-gray boxes. The isolate code, spoligotype designation, year and city of culture isolation, and patient's country of birth are shown on the right. City abbreviations: FI, Firenze (Florence); PO, Prato; SI, Siena; LU, Lucca; PI, Pisa; MS, Massa; PT, Pistoia.