Transmission Dynamics Of Tuberculosis Research Articles

Optimal Control of the Lost to Follow Up in a Tuberculosis Model

This paper deals with the problem of optimal control for the transmission dynamics of tuberculosis (TB). A TB model that considers the existence of a new class (mainly in the African context) is considered: the lost to follow up individuals. Based on the model formulated and studied in the work of Plaire Tchinda Mouofo, (2009), the TB control is formulated and solved as an optimal control theory problem using the Pontryagin's maximum principle (Pontryagin et al., 1992). This control strategy indicates how the control of the lost to follow up class can considerably influence the basic reproduction ratio so as to reduce the number of lost to follow up. Numerical results show the performance of the optimization strategy.

A Probabilistic Transmission Model to Assess Infection Risk fromMycobacterium Tuberculosisin Commercial Passenger Trains

The objective of this article is to characterize the risk of infection from airborne Mycobacterium tuberculosis bacilli exposure in commercial passenger trains based on a risk-based probabilistic transmission modeling. We investigated the tuberculosis (TB) infection risks among commercial passengers by inhaled aerosol M. tuberculosis bacilli and quantify the patterns of TB transmission in Taiwan High Speed Rail (THSR). A deterministic Wells-Riley mathematical model was used to account for the probability of infection risk from M. tuberculosis bacilli by linking the cough-generated aerosol M. tuberculosis bacilli concentration and particle size distribution. We found that (i) the quantum generation rate of TB was estimated with a lognormal distribution of geometric mean (GM) of 54.29 and geometric standard deviation (GSD) of 3.05 quantum/h at particle size ≤ 5 μm and (ii) the basic reproduction numbers (R(0) ) were estimated to be 0.69 (0.06-6.79), 2.82 (0.32-20.97), and 2.31 (0.25-17.69) for business, standard, and nonreserved cabins, respectively. The results indicate that commercial passengers taking standard and nonreserved cabins had higher transmission risk than those in business cabins based on conservatism. Our results also reveal that even a brief exposure, as in the bronchoscopy cases, can also result in a transmission when the quantum generation rate is high. This study could contribute to a better understanding of the dynamics of TB transmission in commercial passenger trains by assessing the relationship between TB infectiousness, passenger mobility, and key model parameters such as seat occupancy, ventilation rate, and exposure duration.

A Theoretical Assessment of the Effects of Smoking on the Transmission Dynamics of Tuberculosis

Smoking has long being associated with tuberculosis. We present a tuberculosis dynamics model taking into account the fact that some people in the population are smoking in order to assess the effects of smoking on tuberculosis transmission. The epidemic thresholds known as the reproduction numbers and equilibria for the model are determined and stabilities analyzed. Qualitative analysis of the model including positivity and persistence of solutions are presented. The model is numerically analyzed to assess the effects of smoking on the transmission dynamics of tuberculosis. Numerical simulations of the model show that smoking enhances tuberculosis transmission, progression to active disease and in a population of smokers, tuberculosis cannot be controlled even when treatment success is assumed to be as high as 88%. Further, analysis of the reproduction numbers indicates that the number of active tuberculosis cases increases as the number of smokers increase.

Clonal expansion of multidrug-resistant and extensively drug-resistant tuberculosis, Japan.

The emergence and spread of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB) has raised public health concern about global control of TB. To estimate the transmission dynamics of MDR and XDR TB, we conducted a DNA fingerprinting analysis of 55 MDR/XDR Mycobacterium tuberculosis strains isolated from TB patients throughout Japan in 2002. Twenty-one (38%) of the strains were classified into 9 clusters with geographic links, which suggests that community transmission of MDR/XDR TB is ongoing. Furthermore, the XDR M. tuberculosis strains were more likely than the non-XDR MDR strains to be clustered (71% vs. 24%; p = 0.003), suggesting that transmission plays a critical role in the new incidence of XDR TB. These findings highlight the difficulty of preventing community transmission of XDR TB by conventional TB control programs and indicate an urgent need for a more appropriate strategy to contain highly developed drug-resistant TB.

The Changing Natural History of Tuberculosis and HIV Coinfection in an Urban Area of Hyperendemicity

Tuberculosis (TB) has proven to be difficult to control in regions with a high prevalence of human immunodeficiency virus (HIV) infection. We previously described high prevalence of HIV infection among adults (23%) and rapidly escalating TB notification rates in a peri-urban township, Site-M in Cape Town, South Africa. The combination of delineated boundaries, a well-characterized population, centralized TB record keeping, and high levels of HIV testing make this population uniquely suited for TB epidemiologic and transmission studies. The driver of the HIV and TB coepidemic appears to be a high annual risk of Mycobacterium tuberculosis infection in this community. A high annual risk of M. tuberculosis infection may be the result of unrecognized infections coupled with intense social interaction and crowding. New non-facility-based interventions will be required, with emphasis on community-based case finding and contact tracing to decrease the infective TB pool. There is a need for better understanding of the transmission dynamics of TB and the intensity of social interactions, which have exacerbated an HIV and TB epidemic in this community of hyperendemicity.

The Transmission Dynamics of Tuberculosis in a Recently Developed Chinese City

BackgroundHong Kong is an affluent subtropical city with a well-developed healthcare infrastructure but an intermediate TB burden. Declines in notification rates through the 1960s and 1970s have slowed since the 1980s to the current level of around 82 cases per 100 000 population. We studied the transmission dynamics of TB in Hong Kong to explore the factors underlying recent trends in incidence.Methodology/Principal FindingsWe fitted an age-structured compartmental model to TB notifications in Hong Kong between 1968 and 2008. We used the model to quantify the proportion of annual cases due to recent transmission versus endogenous reactivation of latent infection, and to project trends in incidence rates to 2018. The proportion of annual TB notifications attributed to endogenous reactivation increased from 46% to 70% between 1968 and 2008. Age-standardized notification rates were projected to decline to approximately 56 per 100 000 in 2018.Conclusions/SignificanceContinued intermediate incidence of TB in Hong Kong is driven primarily by endogenous reactivation of latent infections. Public health interventions which focus on reducing transmission may not lead to substantial reductions in disease burden associated with endogenous reactivation of latent infections in the short- to medium-term. While reductions in transmission with socio-economic development and public health interventions will lead to declines in TB incidence in these regions, a high prevalence of latent infections may hinder substantial declines in burden in the longer term. These findings may therefore have important implications for the burden of TB in developing regions with higher levels of transmission currently.

Optimal control of the transmission dynamics of tuberculosis

This paper deals with the problem of optimal control for the transmission dynamics of tuberculosis (TB). A tuberculosis model which incorporates the essential biological and epidemiological features of the disease such as exogenous reinfection and chemoprophylaxis of latently infected individuals, and treatment of the infectious is developed and rigorously analyzed. Based on this continuous model, the tuberculosis control is formulated and solved as an optimal control theory problem, indicating how a control term on the chemoprophylaxis should be introduced in the population to reduce the number of individuals with active TB. The feedback control law has been proved to be capable of reducing the number of individuals with active TB. An advantage is that the proposed scheme accounts for the energy wasted by the controller and the closed-loop performance on tracking. Numerical results show the performance of the optimization strategy.

Transmission dynamics of pulmonary tuberculosis between autochthonous and immigrant sub-populations

BackgroundThe overall incidence of tuberculosis (TB) in Western Europe has been declining since the 19th Century. However, immigrant sub-groups from high-prevalence countries are slowing down this trend. The aim of this study was to describe how immigration influences TB transmission in Germany. For that we prospectively investigated the dynamics of TB transmission between TB high-prevalence immigrant and TB low-prevalence local populations with molecular epidemiological methods and conventional contact investigations. Besides, we assessed transmission in relation to social mixing using an innovative tool that measures the integration of immigrants into the local social environment.MethodsA prospective study of confirmed culture positive cases of pulmonary TB and their contacts was carried out in a German federal state from 2003 to 2005. Data for the study included: 1) case data routinely collected by the local public health staff and transmitted to the state health office and the national surveillance centre, 2) a study questionnaire designed to capture social interactions of relevance for TB transmission and 3) molecular genotyping data (IS6110 DNA fingerprint and spoligotyping). The proportion of German cases caused by foreign-born cases, and vice versa, was estimated and an integration index was computed using a selected set of questions from the study questionnaire.ResultsA total of 749 cases of culture-positive pulmonary tuberculosis voluntarily enrolled in the study, representing 57.8% of all registered cases diagnosed over the study period. Data that included study questionnaire and DNA fingerprinting were available for 41% (n = 308) of the study participants. Forty-seven clusters, defined as a least two cases infected by the same TB strains, were identified by molecular methods and included 132 (17%) of the study participants. Epidemiological links were identified for 28% of the clusters by conventional epidemiological data. In mixed clusters, defined as clusters including German and foreign-born individuals, the probability of cases to be caused by foreign-born cases was estimated at 18.3%. We observed a trend to mixed clusters with increasing time spent by immigrants in the host country. This group also presented comparatively higher integration indexes than immigrants in immigrant-only clusters.ConclusionOur results confirm the findings of other studies that there is no significant TB transmission from TB high-prevalence immigrant to TB low-prevalence autochthonous population. This may be explained by the good performance of tuberculosis screening programmes for certain groups arriving in Germany from high- prevalence countries, by a low degree of mixing of immigrants with the local population or by a combination of both.

Genomic Diversity among Drug Sensitive and Multidrug Resistant Isolates of Mycobacterium tuberculosis with Identical DNA Fingerprints

Background Mycobacterium tuberculosis complex (MTBC), the causative agent of tuberculosis (TB), is characterized by low sequence diversity making this bacterium one of the classical examples of a genetically monomorphic pathogen. Because of this limited DNA sequence variation, routine genotyping of clinical MTBC isolates for epidemiological purposes relies on highly discriminatory DNA fingerprinting methods based on mobile and repetitive genetic elements. According to the standard view, isolates exhibiting the same fingerprinting pattern are considered direct progeny of the same bacterial clone, and most likely reflect ongoing transmission or disease relapse within individual patients.Methodology/Principal FindingsHere we further investigated this assumption and used massively parallel whole-genome sequencing to compare one drug-susceptible (K-1) and one multidrug resistant (MDR) isolate (K-2) of a rapidly spreading M. tuberculosis Beijing genotype clone from a high incidence region (Karakalpakstan, Uzbekistan). Both isolates shared the same IS6110 RFLP pattern and the same allele at 23 out of 24 MIRU-VNTR loci.We generated 23.9 million (K-1) and 33.0 million (K-2) paired 50 bp purity filtered reads corresponding to a mean coverage of 483.5 fold and 656.1 fold respectively. Compared with the laboratory strain H37Rv both Beijing isolates shared 1,209 SNPs. The two Beijing isolates differed by 130 SNPs and one large deletion. The susceptible isolate had 55 specific SNPs, while the MDR variant had 75 specific SNPs, including the five known resistance-conferring mutations.ConclusionsOur results suggest that M. tuberculosis isolates exhibiting identical DNA fingerprinting patterns can harbour substantial genomic diversity. Because this heterogeneity is not captured by traditional genotyping of MTBC, some aspects of the transmission dynamics of tuberculosis could be missed or misinterpreted. Furthermore, a valid differentiation between disease relapse and exogenous reinfection might be impossible using standard genotyping tools if the overall diversity of circulating clones is limited. These findings have important implications for clinical trials of new anti-tuberculosis drugs.

Epidemiologic Characterization of Culture Positive Mycobacterium tuberculosis Patients by katG-gyrA Principal Genetic Grouping

Molecular typing techniques make it possible to genetically characterize Mycobacterium tuberculosis isolates. Public health strategies to control the spread of tuberculosis are enhanced by the use of molecular data to study tuberculosis transmission dynamics within populations. This study compared epidemiological and clinical characteristics of three M. tuberculosis groups based on polymorphisms at katG codon 463 and gyrA codon 95 in 1893 culture-positive patients by a retrospective nested case-comparison design. Study participants, diagnosed from 1995 to 2001 in the Houston, Texas metropolitan area, were >/= 18 years old, 70% male, 66% U.S.-born, 40% Black, 29% Hispanic, 19% White, and 12% Asian/Pacific Islander. The prevalence of each principal genetic group (GG) was 30% (GG1), 52% (GG2), and 18% (GG3). Multiple logistic regression analysis showed that GG1 participants were more likely to be Asian, male, and have a history of homelessness, as compared with participants with either GG2 or GG3 isolates. GG2 participants were more likely to be Hispanic, have streptomycin-resistant isolates, and be infected with HIV than either GG1 or GG3 participants. GG3 participants were more likely to be Black or Hispanic, report illicit drug use, and live in a congregative facility at the time of diagnosis, than GG1 or GG2 participants. Ethnicity and sociodemographic findings were significant, prompting additional research into social networks, genetic susceptibility, immunology, and virulence factors.

Modelling local and global effects on the risk of contracting Tuberculosis using stochastic Markov-chain models

For some diseases, the transmission of infection can cause spatial clustering of disease cases. This clustering has an impact on how one estimates the rate of the spread of the disease and on the design of control strategies. It is, however, difficult to assess such clustering, (local effects on transmission), using traditional statistical methods. A stochastic Markov-chain model that takes into account possible local or more dispersed global effects on the risk of contracting disease is introduced in the context of the transmission dynamics of tuberculosis. The model is used to analyse TB notifications collected in the Asembo and Gem Divisions of Nyanza Province in western Kenya by the Kenya Ministry of Health/National Leprosy and Tuberculosis Program and the Centers for Disease Control and Prevention. The model shows evidence of a pronounced local effect that is significantly greater than the global effect. We discuss a number of variations of the model which identify how this local effect depends on factors such as age and gender. Zoning/clustering of villages is used to identify the influence that zone size has on the model’s ability to distinguish local and global effects. An important possible use of the model is in the design of a community randomised trial where geographical clusters of people are divided into two groups and the effectiveness of an intervention policy is assessed by applying it to one group but not the other. Here the model can be used to take the effect of case clustering into consideration in calculating the minimum difference in an outcome variable (e.g. disease prevalence) that can be detected with statistical significance. It thereby gauges the potential effectiveness of such a trial. Such a possible application is illustrated with the given time/spatial TB data set.

Mathematical modelling of tuberculosis epidemics

The strengths and limitations of using homogeneous mixing and heterogeneous mixing epidemic models are explored in the context of the transmission dynamics of tuberculosis. The focus is on three types of models: a standard incidence homogeneous mixing model, a non-homogeneous mixing model that incorporates 'household' contacts, and an age-structured model. The models are parameterized using demographic and epidemiological data and the patterns generated from these models are compared. Furthermore, the effects of population growth, stochasticity, clustering of contacts, and age structure on disease dynamics are explored. This framework is used to asses the possible causes for the observed historical decline of tuberculosis notifications.

Human Tuberculosis due toMycobacterium bovisin the United States, 1995–2005

Understanding the epidemiology of human Mycobacterium bovis tuberculosis (TB) in the United States is imperative; this disease can be foodborne or airborne, and current US control strategies are focused on TB due to Mycobacterium tuberculosis and airborne transmission. The National TB Genotyping Service's work has allowed systematic identification of M. tuberculosis-complex isolates and enabled the first US-wide study of M. bovis TB. Results of spacer oligonucleotide and mycobacterial interspersed repetitive units typing were linked to corresponding national surveillance data for TB cases reported for the period 2004-2005 and select cases for the period 1995-2003. We also used National TB Genotyping Service data to evaluate the traditional antituberculous drug resistance-based case definition of M. bovis TB. Isolates from 165 (1.4%) of 11,860 linked cases were identified as M. bovis. Patients who were not born in the United States, Hispanic patients, patients <15 years of age, patients reported to be HIV infected, and patients with extrapulmonary disease each had increased adjusted odds of having M. bovis versus M. tuberculosis TB. Most US-born, Hispanic patients with TB due to M. bovis (29 [90.6%] of 32) had extrapulmonary disease, and their overall median age was 9.5 years. The National TB Genotyping Service's data indicated that the pyrazinamide-based case definition's sensitivity was 82.5% (95% confidence interval; 75.3%-87.9%) and that data identified 14 errors in pyrazinamide-susceptibility testing or reporting. The prevalence of extrapulmonary disease in the young, US-born Hispanic population suggests recent transmission of M. bovis, possibly related to foodborne exposure. Because of its significantly different epidemiologic profile, compared with that of M. tuberculosis TB, we recommend routine surveillance of M. bovis TB. Routine surveillance and an improved understanding of M. bovis TB transmission dynamics would help direct the development of additional control measures.

Multispacer Sequence Typing for Mycobacterium tuberculosis Genotyping

BackgroundGenotyping methods developed to survey the transmission dynamics of Mycobacterium tuberculosis currently rely on the interpretation of restriction and amplification profiles. Multispacer sequence typing (MST) genotyping is based on the sequencing of several intergenic regions selected after complete genome sequence analysis. It has been applied to various pathogens, but not to M. tuberculosis.Methods and FindingsIn M. tuberculosis, the MST approach yielded eight variable intergenic spacers which included four previously described variable number tandem repeat loci, one single nucleotide polymorphism locus and three newly evaluated spacers. Spacer sequence stability was evaluated by serial subculture. The eight spacers were sequenced in a collection of 101 M. tuberculosis strains from five phylogeographical lineages, and yielded 29 genetic events including 13 tandem repeat number variations (44.82%), 11 single nucleotide mutations (37.93%) and 5 deletions (17.24%). These 29 genetic events yielded 32 spacer alleles or spacer-types (ST) with an index of discrimination of 0.95. The distribution of M. tuberculosis isolates into ST profiles correlated with their assignment into phylogeographical lineages. Blind comparison of a further 93 M. tuberculosis strains by MST and restriction fragment length polymorphism-IS6110 fingerprinting and mycobacterial interspersed repetitive units typing, yielded an index of discrimination of 0.961 and 0.992, respectively. MST yielded 41 different profiles delineating 16 related groups and proved to be more discriminatory than IS6110-based typing for isolates containing <8 IS6110 copies (P<0.0003). MST was successfully applied to 7/10 clinical specimens exhibiting a Cts ≤ 42 cycles in internal transcribed spacer-real time PCR.ConclusionsThese results support MST as an alternative, sequencing-based method for genotyping low IS6110 copy-number M. tuberculosis strains. The M. tuberculosis MST database is freely available (http://ifr48.timone.univ-mrs.fr/MST_MTuberculosis/mst).

Comparison of mycobacterial interspersed repetitive unit-variable number tandem repeat and IS6110-RFLP methods in identifying epidemiological links in patients with tuberculosis in Northwest of Iran

In recent years in spite of medical advancement, tuberculosis remains as a worldwide health problem. Therefore, identifying the source of transmission of infection is necessary for decreasing of tuberculosis (TB), also determining the varieties of TB strains by DNA fingerprinting helps to achieve this objective. The aim of present study was to determine tuberculosis transmission dynamics in Northwest of Iran with MIRU-VNTR and IS6110-RFLP methods. MIRU-VNTR performed for analysis of 125 strains and restriction fragment length polymorphism (RFLP) typing was performed on 119 culture-positive specimens during a period of September 2002 to March 2003 in tuberculosis centres of the region. We found 93 distinct MIRU-VNTR patterns, including in 21 clustered patterns and 72 unique patterns from isolated strains. The discriminatory power of MIRU-VNTR typing in our study was high (Hunter-Gaston discriminatory index, HGDI=0.9932) for isolates. Ninety-three distinct IS6110 patterns were revealed. Twelve clusters were found among total of 38 strains. The clusters included 26 patients who infected by 12 another’s. HGDI for our IS6110-RFLP method was 0.9928. The minimum estimate for the proportion of tuberculosis that was due to transmission with IS6110-RFLP was 21.9% and with MIRU-VNTR was 26.4%. In clusters the same patterns of Nakhichevanees patients and Iranian patients were revealed in three clusters with MIRU-VNTR and one cluster in IS6110 which showed that Nakhichevanees patients referred to tuberculosis centres of province could be a source of tuberculosis transmission. RFLP typing has more discriminatory power and it can be concluded that this method is a useful instrument for the better understanding of transmission and the occurrence of micro-epidemics and source tracing.

Molecular typing of Mycobacterium tuberculosis isolates from a rural area of Kanpur by spoligotyping and mycobacterial interspersed repetitive units (MIRUs) typing

Molecular typing of Mycobacterium tuberculosis isolates has greatly facilitated the understanding of epidemiology of tuberculosis (TB). This study was done to characterize prevalent genotypes of M. tuberculosis on a collection of 97 isolates based on spoligotyping and mycobacterial interspersed repetitive units-variable number of tandem repeats (MIRU-VNTR) typing in rural area of Kanpur, North India. In this area different types of interventions are being undertaken and follow-up studies are progressing. Predominant spoligotypes prevalent in this region belonged to Central Asian–Delhi family (CAS1_Del) (37%), East African–Indian family (11%), T1 family (8%) and Beijing (4%) family. Highly distinct MIRU-VNTR genotypes were obtained. Significant spoligotypes such as Beijing and CAS1_Del type were further divided into subtypes with MIRU-VNTR. This preliminary study reveals that CAS is the most predominant family in this rural area of Kanpur. If confirmed in other areas, this combined approach of molecular typing can be preferably be used as first line tool for studying linkage and transmission dynamics of TB in India.

Modeling the impact of immigration on the epidemiology of tuberculosis

This paper presents two new theoretical frameworks to investigate the impact of immigration on the transmission dynamics of tuberculosis. For the basic model, we present new analysis on the existence and stability of equilibria. Then, we use numerical simulations of the model to illustrate the behavior of the system. We apply the model to Canadian reported data on tuberculosis and observe a good agreement between the model prediction and the data. For the extended model, which incorporated the recruitment of the latent and infectious in immigrants to the basic model, we find that the usual threshold condition does not apply and a unique equilibrium exists for all parameter values. This indicates that the disease does not disappear and becomes endemic in host areas. This finding is also supported by numerical simulations with the extended model. Our study suggests that immigrants have a considerable influence on the overall transmission dynamics behavior of tuberculosis.

Molecular clues of a microepidemy among homeless tuberculosis patients in Budapest due to a new and local Mycobacterium tuberculosis clade

In Budapest, the capital of Hungary, one of the most important tuberculosis related risk factor is homelessness. The aim of this retrospective study was the genetic characterization of Mycobacterium tuberculosis strains isolated from 66 homeless tuberculosis patients by spoligotyping and mycobacterial interspersed repetitive unit (MIRU) typing. The study identified a local microepidemy in the district with the highest tuberculosis incidence of Budapest. Further genetic characterization has shown that the microepidemy was due to a locally emerged Budapest-specific lineage of M. tuberculosis. These data may serve as a reference to better monitor and understand the patterns and transmission dynamics of tuberculosis in this at-risk population and is the first report on genetic diversity of M. tuberculosis in today's Hungarians. The findings also indicate that tuberculosis control and prevention steps among the homeless need to be strengthened.

High coverage with HAART is required to substantially reduce the number of deaths from tuberculosis: system dynamics simulation

We used a system dynamics simulation model of the transmission dynamics of drug-sensitive tuberculosis (DSTB), multidrug-resistant tuberculosis (MDRTB) and HIV to estimate the impact of coverage with highly active antiretroviral therapy (HAART) and different cure rates for MDRTB in settings of explosive HIV epidemics and high MDRTB levels. Population coverage levels at 0%, 25%, 50%, 75% and 100% for HAART, and 5% and 80% of MDRTB treatment cure rates were simulated over a 10-year period and cumulative deaths from tuberculosis and HIV-associated tuberculosis were estimated for populations with latent tuberculosis, DSTB, MDRTB, HIV and HIV-associated tuberculosis. Depending on levels of HAART population coverage, increasing MDRTB cure rates from 5% to 80% reduces cumulative tuberculosis deaths by 1% and 13%. High population coverage with HAART (75% or higher), allied with high MDRTB cure rates, reduces cumulative deaths by 60%, with limited impact below this level. High coverage with HAART is required to substantially reduce the number of deaths from tuberculosis.

Social organization and movement influence the incidence of bovine tuberculosis in an undisturbed high‐density badgerMeles melespopulation

1. The culling of European badgers Meles meles has been a central part of attempts to control bovine tuberculosis (TB) in British cattle for many years. Recent results, however, indicate that this approach could in practice enhance disease spread. 2. This paper looks at the relationship between TB incidence and badger ecology in a high-density population in south-west England, which has been the subject of a long-term intensive study. The principal aims were to relate the probability of TB incidence, as detected by culture of clinical samples (i.e. excretion of bacilli), at the level of the individual and of the social group to demographic processes, movement, social organization and disease dynamics. 3. The probability of an individual being an incident case was greater in groups where TB was already present, although this was less influential in groups that were subject to some instability in numbers. Both individuals and groups were more likely to be incident cases where the social group was diminishing in size, although no relationship was observed with group size itself. This suggests that the process of group size reduction rather than group size per se has most influence on disease dynamics. The likelihood that either an individual or a group was an incident case was positively correlated with both individual and group-level movement. When the proportion of females in a social group was high, the positive association between movement and incidence was found to be more pronounced and there was a significantly higher probability of incident cases among males. 4. These relationships highlight the importance of social structure in driving TB transmission dynamics in this stable, high-density badger population. The results support the idea that a stable social structure mitigates against new incident cases of disease, and are consistent with the contention that badger culling may create the social circumstances for enhanced transmission of TB.