from july 2005 through october 2006 , a survey was conducted on 194 isolates of m. tuberculosis obtained from 194 patients with pulmonary tuberculosis ( tb ) ( 1 isolate per patient ) ( 1 ) . patients were recruited from the national hospital for pneumology and phtisiology in cotonou , benin , where most tb patients from the area are treated . cotonou is the largest city in benin , with a population of 655,000 in 2002 and an area of 79 km . the study was approved by the national tuberculosis program board of benin . among these 194 isolates , 17 belonged to the beijing st1 family and exhibited the same 12-loci miru - vntr pattern ( 223325163533 ) . the median age of the patients infected with the m. tuberculosis strains belonging to the beijing genotype ( 28 years ) was similar to that of patients from the general survey ( 30 years ) . demographic data that included date of birth , age , sex , and places of residence and work were collected from each patient . geo - coordinates of each patient s residence and workplace were obtained by using the global positioning system ( gps ) and mapped with the arcview 3.2 software ( esri , redlands , ca , usa ) . seropositive samples were confirmed by a discriminatory hiv1/2 test ( genie ii hiv1/hiv2 ; bio - rad , marnes - la - coquette , france ) . one sputum sample from each patient was decontaminated by using the modified petroff method and cultured in manual mycobacteria growth indicator tube ( mgit ) ( 6 ) and on lwenstein - jensen ( lj ) medium . all isolates were identified as m. tuberculosis complex by the para - nitrobenzoic acid method and tested for drug susceptibility against rifampin , isoniazid , streptomycin , and ethambutol by using the proportion method on lj medium at the following respective concentrations : 40 g / ml , 0.2 g / ml , 4 g / ml , and 2 g / ml ( 7,8 ) . dna was extracted by boiling a suspension of 2 drops of mgit - positive cultures in 300 l of 10 mmol / l tris - hcl and 1 mmol / l edta , ph 8.0 ( 1 tris - edta ) for 5 minutes . miru - vntr typing was performed at genoscreen ( lille , france ) by amplifying each of the 24 independent loci , and results were combined into digit allelic profiles ( 5 ) . all patients discussed here were born in benin and had lived in the country since birth . however , because some inhabitants of cotonou are immigrants from the asian continent , this strain could have been brought into the country by migrant residents of the community . in total , 6 ( 35% ) of 17 patients were hiv-1 seropositive , and the remaining 11 patients ( 65% ) were hiv seronegative . in contrast with the results in the initial survey , the m. tuberculosis beijing strain was more likely to be isolated from hiv seropositive patients than from those who were hiv seronegative ( 21 [ 12% ] of 173 ( p = 0.024 ) . of the 17 m. tuberculosis isolates belonging to the beijing genotype , drug susceptibility testing results were available for 16 . all isolates from the 16 patients were resistant to streptomycin but susceptible to isoniazid , rifampin , and ethambutol . of the remaining 177 isolates from the same survey , drug susceptibility testing was available for 127 , of which only 13 ( 10.2% ) were resistant to streptomycin . the m. tuberculosis beijing strains in this survey were more likely to be resistant to streptomycin than were their non - beijing counterparts ( p<0.001 ) . other researchers have suggested that m. tuberculosis beijing strains may be associated with drug resistance ( 9 ) and that the rapid spread of beijing strains in some settings suggests an intrinsic virulence of this family ( 10 ) . the combination of double alleles in several miru - vntr loci of 1 isolate suggests a mixed infection ( 11 ) . the other 16 strains showed identical profiles in the 24 miru - vntr set : loci 154 , 424 , 577 , 580 , 802 , 960 , 1644 , 1955 , 2059 , 2163b , 2165 , 2347 , 2401 , 2461 , 2531 , 2687 , 2996 , 3007 , 3171 , 3192 , 3690 , 4052 , 4156 , and 4348 with the following profile : 244233342xx4425163353723 . no amplification was achieved for loci 2163b and 2165 , despite 2 rounds of pcr for all 16 isolates . this common failure to amplify loci 2163b and 2165 , which are close in the m. tuberculosis chromosome , might be explained by a chromosomal deletion in the strain responsible for this possible outbreak . having a chromosomal deletion supports the hypothesis that all patients were infected by the same strain . however , other possible explanations such as nucleotide polymorphisms in the sequence complementary to pcr primers could not be excluded . many studies have reported pseudo - outbreaks caused by laboratory cross - contamination ( 12,13 ) . this is not likely in the present study because almost all the specimens for primary culture were processed on different days over several months . mapping of patients residences and workplaces showed that many lived or worked ( or both ) in the xwlacodji area of cotonou ( figure ) . to further investigate this spatial cluster and a possible link between patients , we mapped a place they habitually frequented and found that most patronized the same drinking bar ( figure ) . ten of the patients either lived or worked near the bar ( < 300 m ) or regularly visited it . although no epidemiologic link was evident between these patients and the remaining 7 patients , most of the latter were motorcycle taxi drivers and regularly moved from place to place . maps showing residences and workplaces of mycobacterium tuberculosis patients in xwlacodji , cotonou , benin , 20052006 . without gps we could not have identified the geographic cluster of these patients with beijing strains in xwlacodji . the residents are poor , and overcrowding creates conditions favorable for transmission of diseases from person to person and rapid spread of the resistant m. tuberculosis beijing strain . we can not completely exclude the unlikely possibility that the patients were infected by different strains with the same miru - vntr pattern . however , the 17 strains identical 24-loci miru - vntr profile , with a probable deletion of the same 2 loci ; the identical drug susceptibility pattern ( monoresistant to streptomycin ) ; and the fact that most patients resided in the same community as determined by gis strongly suggest that these strains are part of an outbreak . generally , molecular tools are used to study tb transmission and to suggest possible outbreaks . gis has rarely been used in health systems , particularly in resource - poor countries such as benin ( 14 ) . gis tools might be dispensable in industrialized countries where streets and houses are properly mapped and pinpointing specific addresses is generally sufficient to localize an outbreak . in many low - income settings , however , streets and houses are not properly numbered and mapped , and using gps is necessary to gain access to accurate geo - coordinates and localize such outbreaks . in the absence of genetic methods , differentiating cases from the same route of transmission from others however , gis can help tb control practitioners identify areas with aggregate cases so they can institute appropriate measures to control the disease .