A chain-binomial model for intra-household spread of Mycobacterium tuberculosis in a low socio-economic setting in Pakistan

Transmission Modeling with Regression Adjustment for Analyzing Household-based Studies of Infectious Disease: Application to Tuberculosis

BACKGROUND

Household contacts of people infected with a transmissible disease may be at risk due to this proximate exposure, or from other unobserved sources. Understanding variation in infection risk is essential for targeting interventions.

METHODS

We develop an analytical approach to estimate household and exogenous forces of infection, while accounting for individual-level characteristics that affect susceptibility to disease and transmissibility. We apply this approach to a cohort study conducted in Lima, Peru, of 18,544 subjects in 4,500 households with at least one active tuberculosis (TB) case and compare the results to those obtained by Poisson and logistic regression.

RESULTS

HIV-coinfected (susceptibility hazard ratio [SHR] = 3.80, 1.56-9.29), child (SHR = 1.72, 1.32-2.23), and teenage (SHR = 2.00, 1.49-2.68) household contacts of TB cases experience a higher hazard of TB than do adult contacts. Isoniazid preventive therapy (SHR = 0.30, 0.21-0.42) and Bacillus Calmette-Guérin (BCG) vaccination (SHR = 0.66, 0.51-0.86) reduce the risk of disease among household contacts. TB cases without microbiological confirmation exert a smaller hazard of TB among their close contacts compared with smear- or culture-positive cases (excess hazard ratio = 0.88, 0.82-0.93 for HIV- cases and 0.82, 0.57-0.94 for HIV+ cases). The extra household force of infection results in 0.01 (95% confidence interval [CI] = 0.004, 0.028) TB cases per susceptible household contact per year and the rate of transmission between a microbiologically confirmed TB case and susceptible household contact at 0.08 (95% CI = 0.045, 0.129) TB cases per pair per year.

CONCLUSIONS

Accounting for exposure to infected household contacts permits estimation of risk factors for disease susceptibility and transmissibility and comparison of within-household and exogenous forces of infection.

Epidemiology of tuberculosis and treatment outcomes among children in Pakistan: a 5 year retrospective study

Background

Regardless of the advancement in medical technologies, the diagnosis of tuberculosis (TB) in children has remained a challenge. Childhood TB is rampant and an important cause of morbidity and mortality. The objective of this study was to determine the trend of TB and treatment outcomes in children aged ≤14 years registered for TB treatment under DOTS course in three districts of Sindh, Pakistan.

Methods

For this retrospective study, records of TB children (≤14 years) registered for the treatment of TB from January 2011 to December 2015 in three districts of Pakistan, were collected. Demographic data, baseline weight, clinical manifestations, radiography, histopathology results and treatment outcomes were collected from TB unit registers.

Results

A total of 2,167 children were treated for TB during the study period. Of these, 1,199 (55.3%) were females and 1,242 (57.3%) were from urban areas. Over three-quarter of patients (76.9%) had pulmonary TB with 13.3% of sputum smear positive cases. The overall treatment success rate was 92.4%. In multivariate analysis, rural residents (OR: 2.146, p < 0.001), sputum smear positive cases (OR: 3.409, p < 0.001) and re-treated patients (OR: 5.919, p < 0.001), were significantly associated with unsuccessful treatment outcomes. However, age group ≤2 years, male and those who were underweight were found to have the highest risk of pulmonary tuberculosis (OR: 1.953, p < 0.001; OR: 1.262, p = 0.028; OR: 1.342, p = 0.008), respectively.

Conclusion

Patients at risk of treatment failure must be given particular attention. Moreover, strategies are needed to further improve the diagnosis and treatment of TB among children and improve the recording system.

Type of Treatment Supporters in Successful Completion of Tuberculosis Treatment: A Retrospective Cohort Study in Pakistan

Background

The World Health Organization has recommended a patient-centered approach to tuberculosis drug administration. A central element of the patient-centered strategy is the use of treatment supporters to evaluate and elevate adherence to the treatment regimen and to address poor adherence when it occurs. This study was led to determine the part of various treatment supporters in the successful completion of treatment.

Method

This study was conducted in two locales of Sindh, Hyderabad and Mirpurkhas. Information gathered included age, gender, regions, sort of treatment supporters (relatives, community and health facility workers) and treatment outcomes.

Results

Of the 773 patients incorporated into the study, 86.8% picked a family supporter, 7.63% selected community worker and 5.56% chose health facility worker as their treatment supporter. Women and younger patients were more likely to prefer that family members supervise their treatment. Treatment achievement rates among the patients regulated by the three kinds of treatment supporters, were not altogether unique in relation to each other (p=0.23 Chi square).

Conclusion

The study demonstrates that TB patients ought to be urged to pick the supporter of their inclination as selection of treatment supporter outside the health system does not adversely affect TB treatment outcomes in limited resource settings.

Polymorphisms of IFN-γ (+874A/T) and IL-12 (+1188A/C) in tuberculosis patients and their household contacts in Hyderabad, India

Several cytokine gene variants have shown to be associated with host susceptibility to infectious diseases including tuberculosis (TB). High rates of transmission were identified within household members of TB patients. In this study, we examined whether single nucleotide polymorphisms of IFN-γ +874A/T and IL-12 +1188A/C affect susceptibility to TB. Genomic DNA from patients with active disease, their household contacts HHC and healthy controls HC was genotyped for IFN-γ +874A/T and IL-12 +1188A/C SNPs by amplification refractory mutation system-polymerase chain reaction (ARMS-PCR). IFN-γ +874 AA and AT genotypes were significantly with different frequencies in patients and total HHC as compared to HC (p<0.0001). In patients IL-12 +1188 AC and CC genotypes were associated with TB (p<0.003, p<0.008). In total HHC AC, CC genotypes and both alleles (A&C) were significantly different as compared to HC (p<0.004, p<0.001, p<0.034) and the same result was obtained when HHC were stratified into related (p<0.02, p<0.001) and unrelated (p<0.009, p<0.017) individuals. Allelic frequencies, however, were significant only in related contacts (p<0.021). Generalized multifactor dimensionality reduction method (GMDR) testing revealed high risk combinations of several genotypes in IFN-γ & IL-12 genes. Our findings suggest an important role of genetic variations of IFN-γ and IL-12 for susceptibility to TB.

Tuberculosis control in Sindh, Pakistan: Critical analysis of its implementation

Tuberculosis (TB) remains one of the main health problems despite preventive and control measures that have been taken in the past few decades. It is responsible for almost 8.8 million cases and 1.4 million deaths around the world. Lack of access to TB services is a barrier for empowering TB patients. In a country like Pakistan, controlling TB has become a challenge because of the lack of private sector involvement in a National Tuberculosis Control Program (NTP). Therefore, collaboration is needed between public, private and government sectors in treating TB as well as in improving the quality of the health care system.

Association of IL-1β +3954 C/T and IL-10-1082 G/A cytokine gene polymorphisms with susceptibility to tuberculosis

Tuberculosis (TB) constitutes the major cause of death due to infectious diseases. Cytokines play a major role in defence against Mycobacterium tuberculosis infection. Polymorphisms in the genes encoding various cytokines have been associated with tuberculosis susceptibility. Household contacts (HHC) are at increased risk of developing the disease. In this study, we examined the association of IL-1β and IL-10 cytokine gene polymorphisms with risk of developing tuberculosis in TB patients, their HHC and healthy controls (HC) using JavaStat and SPSS. Multifactor dimensionality reduction (MDR) analyses were performed to explore the potential gene-gene interactions. The genotype and allele frequencies of IL-1β +3954C/T polymorphism did not vary significantly between TB patients and HC. GG (P < 0.005, OR = 0.219 and 95% CI = 0.059-0.735) and GA (P < 0.0001, OR = 2.938 and 95% CI = 1.526-5.696) genotypes of IL-10-1082 G/A polymorphism were found to be significantly associated with patients versus HC. HHC with CC (P < 0.03, OR = 1.833 and 95% CI = 1.1-3.35) genotype in IL-1β and GA (P < 0.0001, OR = 4.612 and 95% CI = 2.225-9.702) genotype in IL-10 were at increased risk of developing tuberculosis. MDR tests revealed high-risk genotypes in IL-1β and IL-10 based on the association model. Our results demonstrate that the polymorphisms of IL-1β and IL-10 genes may be valuable markers to predict the risk for the development of TB in household contacts.

Epidemiologic inference from the distribution of tuberculosis cases in households in Lima, Peru

BACKGROUND

Tuberculosis (TB) often occurs among household contacts of people with active TB. It is unclear whether clustering of cases represents household transmission or shared household risk factors for TB.

METHODS

We used cross-sectional data from 764 households in Lima, Peru, to estimate the relative contributions of household and community transmission, the average time between cases, and the immunity afforded by a previous TB infection.

RESULTS

The distribution of cases per household suggests that almost 7 of 10 nonindex household cases were infected in the community rather than in the household. The average interval between household cases was 3.5 years. We observed a saturation effect in the number of cases per household and estimated that protective immunity conferred up to 35% reduction in the risk of disease.

CONCLUSIONS

Cross-sectional household data can elucidate the natural history and transmission dynamics of TB. In this high-incidence setting, we found that the majority of cases were attributable to community transmission and that household contacts of case patients derive some immunity from household exposures. Screening of household contacts may be an effective method of detecting new TB cases if carried out over several years.

Cytokine gene polymorphisms across tuberculosis clinical spectrum in Pakistani patients

BACKGROUND

Pakistan ranks 7(th) globally in terms of tuberculosis (TB) disease burden (incidence 181/100000 pop./yr; prevalence of 329/pop./yr). Reports from different populations show variable associations of TB susceptibility and severity with cytokine gene polymorphisms. Tuberculosis clinical severity is multi-factorial and cytokines play a pivotal role in the modulation of disease severity. We have recently reported that the ratio of two key cytokines (IFNgamma and IL10) show significant correlation with the severity spectrum of tuberculosis. The objective of the current study was to analyze the frequency of cytokine gene polymorphisms linked to high and low responder phenotypes (IFNgamma +874 T(hi)-->A(lo) and IL10 -1082 G(lo)-->A(hi)) in tuberculosis patients.

METHODS AND FINDINGS

STUDY GROUPS WERE STRATIFIED ACCORDING TO DISEASE SITE AS WELL AS DISEASE SEVERITY: Pulmonary N = 111 (Minimal, PMN = 19; Moderate, PMD = 63; Advance, PAD = 29); Extra-pulmonary N = 67 (Disseminated DTB = 20, Localized LTB = 47) and compared with healthy controls (TBNA = 188). Genotype analyses were carried out using amplification refractory mutation system-PCR (ARMS-PCR) and stimulated whole blood (WB) culture assay was used for assessing cytokine profiles. Our results suggest that the IFNgamma +874 TT genotype and T allele was overrepresented in PMN (p = 0.01) and PMD (p = 0.02). IFNgamma +874 TT in combination with IL10 GG(lo) genotypes showed the highest association (chi(2) = 6.66, OR = 6.06, 95% CI = 1.31-28.07, p = 0.01). IFNgamma AA(lo) on the other hand in combination with IL10 GG(lo) increased the risk of PAD (OR = 5.26; p = 0.005) and DTB (OR = 3.59; p = 0.045).

CONCLUSION

These findings are consistent with the role of IL10 in reducing collateral tissue damage and the protective role of IFNgamma in limiting disease in the lung.

Longitudinal tracking of cytokines after acute exposure to tuberculosis: association of distinct cytokine patterns with protection and disease development

Household contacts (HCs) of patients with tuberculosis (TB) are at higher risk of infection as well as the development of active disease. Longitudinal tracking of antigen-specific cytokines after acute exposure may significantly advance our understanding of the dynamic changes in cytokine patterns associated with disease establishment. To achieve this objective, we carried out a prospective cohort study with healthy HCs after exposure to TB. The patterns of cytokines (gamma interferon [IFN-gamma] and interleukin 10 [IL-10]) in response to mycobacterial antigens (culture filtrate [CF] proteins) and nonspecific mitogens (phytohemagglutinin [PHA] and lipopolysaccharide [LPS]) were assessed at 0, 6, 12, and 24 months after exposure. Seven of 109 (6.4%) HCs developed active disease. Six of the seven individuals were females, and active disease developed between 12 and 15 months after exposure in 5/20 families. The most significant findings were the exponential increases ( approximately 1,000-fold) in both the CF protein- and the PHA- or LPS-induced IFN-gamma/IL-10 ratio in healthy HCs (n = 26), which peaked at 12 months, compared to the levels in HCs who developed disease (n = 7), in whom relatively flat responses were observed during the 24-month period. Linear trends for 0 to 12 and 0 to 24 months for the CF protein-induced IFN-gamma/IL-10 ratio showed significant differences between the two groups, as determined by the use of the Mantel extension test for chi(2) analysis (odds ratio = 0.45; 95% confidence interval = 0.295 to 0.685; P = 0.0002). Our results strongly suggest that the magnitude of the IFN-gamma/IL-10 ratio at 12 months after exposure may be a critical determinant in the resolution of infection. These studies provide new insights into the cytokine responses associated with disease establishment or the resolution of infection after natural exposure to TB and have implications for TB control programs as well vaccine efficacy studies.