The epidemiology of tuberculosis in San Francisco. A population-based study using conventional and molecular methods.
ABSTRACT The epidemiology of tuberculosis in urban populations is changing. Combining conventional epidemiologic techniques with DNA fingerprinting of Mycobacterium tuberculosis can improve the understanding of how tuberculosis is transmitted.
We used restriction-fragment-length polymorphism (RFLP) analysis to study M. tuberculosis isolates from all patients reported to the tuberculosis registry in San Francisco during 1991 and 1992. These results were interpreted along with clinical, demographic, and epidemiologic data. Patients infected with the same strains were identified according to their RFLP patterns, and patients with identical patterns were grouped in clusters. Risk factors for being in a cluster were analyzed.
Of 473 patients studied, 191 appeared to have active tuberculosis as a result of recent infection. Tracing of patients' contacts with the use of conventional methods identified links among only 10 percent of these patients. DNA fingerprinting, however, identified 44 clusters, 20 of which consisted of only 2 persons and the largest of which consisted of 30 persons. In patients under 60 years of age, Hispanic ethnicity (odds ratio, 3.3; P = 0.02), black race (odds ratio, 2.3; P = 0.02), birth in the United States (odds ratio, 5.8; P < 0.001), and a diagnosis of the acquired immunodeficiency syndrome (odds ratio, 1.8; P = 0.04) were independently associated with being in a cluster. Further study of patients in clusters confirmed that poorly compliant patients with infectious tuberculosis have a substantial adverse effect on the control of this disease.
Despite an efficient tuberculosis-control program, nearly a third of new cases of tuberculosis in San Francisco are the result of recent infection. Few of these instances of transmission are identified by conventional contact tracing.
Full-textDOI: · Available from: Julie Parsonnet, Nov 04, 2014
SourceAvailable from: Francesca Barletta[Show abstract] [Hide abstract]
ABSTRACT: Sputum samples from new tuberculosis (TB) cases were collected over two years as part of a prospective study in the North-eastern of Lima, Peru. To measure the contribution of recent transmission to the high multi-drug resistance (MDR) rates in this area, Mycobacterium tuberculosis complex (MTBc) isolates were tested for drug susceptibility to first-line drugs and genotyped by spoligotyping and 15-loci Mycobacterial Interspersed Repetitive Unit-Variable Number of Tandem Repeats (MIRU-15). MDR-TB was found in 6.8% of 844 isolates, of which 593 (70.3%) were identified as belonging to a known MTBc lineage, whereas 198 (23.5%) could not be assigned to these lineages and 12 (1.4%) were mixed infections. Lineage 4 accounted for 54.9% (n=463) of the total, most of which belonged to the Haarlem family (n=279). MIRU-15 grouped 551/791 (69.7%) isolates in 102 clusters, with sizes ranging from 2 to 46 strains. The overall high clustering rate suggests a high level of recent transmission in this population, especially among younger patients (OR 1.6; p=0.01). Haarlem strains were more prone to cluster compared to the other families taken together (OR 2.0; p<0.0001), while Beijing (OR 0.6; p=0.006) and LAM (OR 0.7; p=0.07) strains clustered less. Where streptomycin-resistant strains were more commonly found in clusters (OR 1.8; p=0.03), clustering between MDR and non-MDR strains did not differ (OR 1.8; p=0.1). Furthermore, only 16/51 MDR strains clustered with other MDR strains, suggesting that patients with primary MDR have acquired this infection mostly from index cases outside the study population, such as retreatment cases. Copyright © 2015, American Society for Microbiology. All Rights Reserved.Journal of clinical microbiology 03/2015; DOI:10.1128/JCM.03585-14 · 4.23 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: To improve understanding of the factors influencing tuberculosis transmission and the role of pathogen variation, we sequenced all available specimens from patients diagnosed over 15 years in a whole district in Malawi. Mycobacterium tuberculosis lineages were assigned and transmission networks constructed, allowing ≤10 single nucleotide polymorphisms (SNPs) difference. We defined disease as due to recent infection if the network-determined source was within 5 years, and assessed transmissibility from forward transmissions resulting in disease. High-quality sequences were available for 1687 disease episodes (72% of all culture-positive episodes): 66% of patients linked to at least one other patient. The between-patient mutation rate was 0.26 SNPs/year (95% CI 0.21-0.31). We showed striking differences by lineage in the proportion of disease due to recent transmission and in transmissibility (highest for lineage-2 and lowest for lineage-1) that were not confounded by immigration, HIV status or drug resistance. Transmissions resulting in disease decreased markedly over time.eLife Sciences 03/2015; 4:e05166. DOI:10.7554/eLife.05166 · 8.52 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Tuberculosis (TB) outbreak occurred in a boarding middle school of China. We explored its probable sources and quantified the transmissibility and pathogenicity of TB. Clinical evaluation, tuberculin skin testing and chest radiography were conducted to identify TB cases. Mycobacterium tuberculosis isolates underwent genotyping analysis to identify the outbreak source. A chain-binomial transmission model was used to evaluate transmissibility and pathogenicity of TB. A total of 46 active cases were ascertained among 258 students and 15 teachers/staff, an attack rate of 16.8%. Genetic analyses revealed two groups of M. tuberculosis cocirculating during the outbreak and possible importation from local communities. Secondary attack rates among students were 4.1% (2.9%, 5.3%) within grade and 7.9% (4.9%, 11%) within class. An active TB case was estimated to infect 8.4 (7.2, 9.6) susceptible people on average. The smear-positive cases were 28 (8, 101) times as infective as smear-negative cases. Previous BCG vaccination could reduce the probability of developing symptoms after infection by 70% (1.4%, 91%). The integration of clinical evaluation, genetic sequencing, and statistical modeling greatly enhanced our understanding of TB transmission dynamics. Timely diagnosis of smear-positive cases, especially in the early phase of the outbreak, is the key to preventing further spread among close contacts. Copyright © 2015. Published by Elsevier B.V.Infection Genetics and Evolution 03/2015; 32:148-155. DOI:10.1016/j.meegid.2015.03.001 · 3.26 Impact Factor