Re-emergence of the progenitors of a multidrug-resistant outbreak strain of Mycobacterium tuberculosis among the post-outbreak case patients.

BACKGROUND. The progenitors of multidrug-resistant tuberculosis (MDR-TB) outbreak strains might evolve into new outbreak strains. We hypothesized that these strains could re-emerge among post-outbreak patients with TB and must thus be tracked. METHODS. To identify the progenitors of the outbreak strain, we first determined the precise IS6110 genomic insertion locations of a Haarlem3 strain that caused a severe MDR-TB outbreak in Tunisia. Next, we searched by polymerase chain reaction for these outbreak-specific IS6110 transposition sites in all the Haarlem3 post-outbreak isolates recovered in the epidemic region. RESULTS. By analyzing the distribution of the outbreak-specific IS6110 transposition sites, we were able to trap, among isolates recovered from post-outbreak new patients, drug-susceptible and drug-resistant isolates that are likely to represent the very close progenitors of the outbreak strain. Mycobacterial interspersed repetitive units-variable number of tandem repeats typing and sequential accumulation of rifampicin resistance-associated rpoB mutations further confirmed the identity of the outbreak's progenitor strains. CONCLUSIONS. The data of the current study show that the progenitors of an MDR-TB outbreak strain could re-emerge among post-outbreak TB cases. We provide an IS6110 insertion site-based approach to better trace back the events preceding the emergence of MDR-TB outbreaks, irrespective of the availability of a pre-outbreak strain collection.

Genetic profiling of Mycobacterium tuberculosis in Tunisia: predominance and evidence for the establishment of a few genotypes.

Typing analyses of 378 Mycobacterium tuberculosis isolates collected between the years 2001 and 2005 from three northern representative regions of Tunisia revealed a highly homogeneous population. Indeed, 84.9 % of all tuberculosis (TB) cases were attributed to the Haarlem, LAM or T families. Strikingly, within each family, more than 60 % of TB cases were due to a single genotype. ST50 (Haarlem3) and ST42 (LAM9) genotypes were exceptionally predominant, representing 46.3 % of all typed isolates. ST50 showed an increased tendency for clustering and was more predominant in the extreme north of the country. By contrast, the more widespread ST42, which was apparently prevalent 17 years ago, displayed weak cluster individualization and a low transmission rate, consistent with its stable association with the Tunisian population. It is believed that both mass BCG vaccination, strictly applied for four decades, and the high endogamy rate that characterizes the Tunisian population could have profoundly shaped the population structure of M. tuberculosis by concurrently favouring the selection and accommodation of particular genotypes.

Promoter and neck region length variation of DC-SIGN is not associated with susceptibility to tuberculosis in Tunisian patients.

The C-type lectin DC-SIGN (CD209) is an important pathogen recognition receptor of the innate immune system. Recent studies showed that DC-SIGN is the major receptor of Mycobacterium tuberculosis on human dendritic cells and that polymorphisms in the DC-SIGN promoter region are associated with susceptibility to tuberculosis. In this light, we aimed to study the potential implication of DC-SIGN genetic variation in the predisposition to tuberculosis in a group of Tunisian patients. We thus performed an association study comprising 138 tuberculosis patients and 140 healthy controls. Sequencing of the DC-SIGN promoter region detected four polymorphisms (-939, -871, -601, and -336), but no differences in their allelic distribution were observed between the two groups. In addition, the analysis of length variation in the DC-SIGN neck region indicated extremely low levels of polymorphisms and, again, no differences between patients and controls. Our data showed therefore that neither promoter variants nor length variation in the neck region of DC-SIGN is associated with susceptibility to tuberculosis in Tunisian patients.

MDR-TB Outbreak among HIV-Negative Tunisian Patients followed during 11 Years.

BACKGROUND: Multidrug-resistant tuberculosis (MDR-TB) outbreaks that evolve, from the outset, in a context strictly negative for HIV infection deserve special consideration since they reflect the true intrinsic epidemic potential of the causative strain. To our knowledge, the long-term evolution of such exceptional outbreaks and the treatment outcomes for the involved patients has never been reported hitherto. Here we provide a thorough description, over an 11-year period, of an MDR-TB outbreak that emerged and expanded in an HIV-negative context, Northern Tunisia. METHODOLOGY/PRINCIPAL FINDINGS: From October 2001 to June 2011, the MDR-TB outbreak involved 48 HIV-negative individuals that are mainly young (mean age 31.09 yrs; 89.6% male) and noninstitutionalized. Drug susceptibility testing coupled to mutational analysis revealed that initial transmission involved an isolate that was simultaneously resistant to isoniazid, rifampicin, ethambutol, and streptomycin. The causative Haarlem3-ST50 outbreak strain expanded mainly as an 11-banded IS6110 RFLP profile (77.1%), from which a 12-banded subclone evolved. After undergoing a 2-year treatment with second-line drugs, 22 (45.8%) patients were cured and 3 (6.2%) completed treatment, thus yielding an overall treatment success rate of 52.1%. Among the patients that experienced unfavorable treatment outcomes, 10 (20.8%) failed treatment, 3 (6.2%) were lost to follow-up, 5 (10.4%) died, and 5 (10.4%) could not be evaluated. Poor adherence to treatment was found to be the main independent predictor of unfavorable outcomes (HR: 9.15; 95% CI 1.72-48.73; P = 0.014). Intriguingly, the evolved 12-banded subclone proved significantly associated with unfavorable outcomes (HR: 4.90; 95% CI 1.04-23.04, P = 0.044). High rate of fatality and relapse was further demonstrated at the long-term, since 70% of those whose treatment failed have died, and 24% among those deemed successfully treated have relapsed. CONCLUSIONS/SIGNIFICANCE: Taken together, the data obtained in this study indicate that MDR-TB clinical isolates could become fit enough to cause large and severe outbreaks in an HIV-negative context. Such MDR-TB outbreaks are characterized by low treatment success rates and could evolve towards increased severity, thus calling for early detection of cases and the necessity to raise the bar of surveillance throughout and beyond the treatment period.

Tuberculosis due to resistant Haarlem strain, Tunisia.

Multidrug-resistant tuberculosis was diagnosed in 21 HIV-negative, nonhospitalized male patients residing in northern Tunisia. A detailed investigation showed accelerated transmission of a Mycobacterium tuberculosis clone of the Haarlem type in 90% of all patients. This finding highlights the epidemic potential of this prevalent genotype.