Transmission of Mycobacterium tuberculosis from tuberculosis patients with HIV infection or AIDS

Transmission Dynamics in Tuberculosis Patients with Human Immunodeficiency Virus: A Systematic Review and Meta-Analysis of 32 Observational Studies

BACKGROUND

There are large knowledge gaps on the transmission dynamics of Mycobacterium tuberculosis in settings where both tuberculosis and HIV are endemic. We aimed to assess the infectiousness of tuberculosis patients coinfected with HIV.

METHODS

We systematically searched for studies of contacts of both HIV-positive and negative tuberculosis index cases. Our primary outcome was Mycobacterium tuberculosis infection in contacts. Data on sputum smear and lung cavitation status of index cases was extracted from each study to assess effect modification. Secondary outcomes included prevalent tuberculosis and HIV in contacts of HIV-positive and negative index cases.

RESULTS

Of 5,255 original citations identified, 32 studies met inclusion criteria including 25 studies investigating M. tuberculosis infection (Nparticipants=36,893), 13 on tuberculosis (Nparticipants=18,853), and 12 on HIV positivity (Nparticipants=18,424). Risk of M. tuberculosis infection was lower in contacts of HIV-positive index cases (Odds Ratio [OR], 0.67, 95% CI, 0.58-0.77) but was heterogeneous (I2=75.1%). Two factors modified this relationship: the lung cavitary status of the index case and immunosuppression (measured through CD4 counts or HIV or AIDS diagnoses) among index patients living with HIV. Rates of HIV were consistently higher in contacts of coinfected index cases (OR, 4.9, 95% CI, 3.0-8.0). This was modified by whether the study was in sub-Saharan Africa (OR, 2.8, 1.6-4.9) or in another global region (OR, 9.8, 5.9-16.3).

CONCLUSIONS

Tuberculosis patients coinfected with HIV are less infectious than HIV-uninfected cases when they have severe immunosuppression or paucibacillary disease. Contacts of coinfected index cases are almost five times more likely to also have HIV.

Does antiretroviral treatment increase the infectiousness of smear-positive pulmonary tuberculosis?

BACKGROUND

Understanding of the effects of human immunodeficiency virus (HIV) infection and antiretroviral treatment (ART) on Mycobacterium tuberculosis transmission dynamics remains limited. We undertook a cross-sectional study among household contacts of smear-positive pulmonary tuberculosis (TB) cases to assess the effect of established ART on the infectiousness of TB.

METHOD

Prevalence of tuberculin skin test (TST) positivity was compared between contacts of index cases aged 2-10 years who were HIV-negative, HIV-positive but not on ART, on ART for <1 year and on ART for 1 year. Random-effects logistic regression was used to take into account clustering within households.

RESULTS

Prevalence of M. tuberculosis infection in contacts of HIV-negative patients, HIV-positive patients on ART 1 year and HIV-positive patients not on ART/on ART <1 year index cases was respectively 44%, 21% and 22%. Compared to contacts of HIV-positive index cases not on ART or recently started on ART, the odds of TST positivity was similar in contacts of HIV-positive index cases on ART 1 year (adjusted OR [aOR] 1.0, 95%CI 0.3-3.7). The odds were 2.9 times higher in child contacts of HIV-negative index cases (aOR 2.9, 95%CI 1.0-8.2).

CONCLUSIONS

We found no evidence that established ART increased the infectiousness of smear-positive, HIV-positive index cases.

Risk ratios for contagious outcomes

Epidemiologists commonly use the risk ratio to summarize the relationship between a binary covariate and outcome, even when outcomes may be dependent. Investigations of transmissible diseases in clusters-households, villages or small groups-often report risk ratios. Epidemiologists have warned that risk ratios may be misleading when outcomes are contagious, but the nature of this error is poorly understood. In this study, we assess the meaning of the risk ratio when outcomes are contagious. We provide a mathematical definition of infectious disease transmission within clusters, based on the canonical stochastic susceptible-infective model. From this characterization, we define the individual-level ratio of instantaneous infection risks as the inferential target, and evaluate the properties of the risk ratio as an approximation of this quantity. We exhibit analytically and by simulation the circumstances under which the risk ratio implies an effect whose direction is opposite that of the true effect of the covariate. In particular, the risk ratio can be greater than one even when the covariate reduces both individual-level susceptibility to infection, and transmissibility once infected. We explain these findings in the epidemiologic language of confounding and Simpson's paradox, underscoring the pitfalls of failing to account for transmission when outcomes are contagious.

Infectiousness of HIV-Seropositive Patients with Tuberculosis in a High-Burden African Setting

RATIONALE

Policy recommendations on contact investigation of HIV-seropositive patients with tuberculosis have changed several times. Current epidemiologic evidence informing these recommendations is considered low quality, and few large studies investigating the infectiousness of HIV-seropositive and -seronegative index cases have been performed in sub-Saharan Africa.

OBJECTIVES

We assessed the infectiousness of HIV-seropositive and -seronegative patients with tuberculosis to their household contacts and examined potential modifiers of this relationship.

METHODS

Adults suffering from their first episode of pulmonary tuberculosis were identified in Kampala, Uganda. Field workers visited index households and enrolled consenting household contacts. Latent tuberculosis infection was measured through tuberculin skin testing, and relative risks were calculated using modified Poisson regression models. Standard assessments of interaction between latent tuberculosis infection, the HIV serostatus of index cases, and other variables were performed.

MEASUREMENTS AND MAIN RESULTS

Latent tuberculosis infection was found in 577 of 878 (65.7%) and 717 of 974 (73.6%) household contacts of HIV-seropositive and -seronegative tuberculosis cases (relative risk, 0.89; 95% confidence interval, 0.82-0.97). On further stratification, cavitary lung disease (P < 0.0001 for interaction) and smear status (P = 0.02 for interaction) of tuberculosis cases modified the infectiousness of HIV-seropositive indexes. Cough duration of index cases did not display interaction (P = 0.499 for interaction).

CONCLUSIONS

This study suggests that HIV-seropositive tuberculosis cases may be less infectious than HIV-seronegative patients only when they are smear-negative or lack cavitary lung disease. These results may explain heterogeneity between prior studies and provide evidence suggesting that tuberculosis contact investigation should include HIV-seropositive index cases in high disease burden settings.

Impact of co-infections and BCG immunisation on immune responses among household contacts of tuberculosis patients in a Ugandan cohort

BACKGROUND

Tuberculosis incidence in resource poor countries remains high. We hypothesized that immune modulating co-infections such as helminths, malaria, and HIV increase susceptibility to latent tuberculosis infection (LTBI), thereby contributing to maintaining the tuberculosis epidemic.

METHODS

Adults with sputum-positive tuberculosis (index cases) and their eligible household contacts (HHCs) were recruited to a cohort study between May 2011 and January 2012. HHCs were investigated for helminths, malaria, and HIV at enrolment. HHCs were tested using the QuantiFERON-TB Gold In-Tube (QFN) assay at enrolment and six months later. Overnight whole blood culture supernatants from baseline QFN assays were analyzed for cytokine responses using an 11-plex Luminex assay. Associations between outcomes (LTBI or cytokine responses) and exposures (co-infections and other risk factors) were examined using multivariable logistic and linear regression models.

RESULTS

We enrolled 101 index cases and 291 HHCs. Among HHCs, baseline prevalence of helminths was 9% (25/291), malaria 16% (47/291), HIV 6% (16/291), and LTBI 65% (179/277). Adjusting for other risk factors and household clustering, there was no association between LTBI and any co-infection at baseline or at six months: adjusted odds ratio (95% confidence interval (CI); p-value) at baseline for any helminth, 1.01 (0.39-2.66; 0.96); hookworm, 2.81 (0.56-14.14; 0.20); malaria, 1.06 (0.48-2.35; 0.87); HIV, 0.74 (0.22-2.47; 0.63). HHCs with LTBI had elevated cytokine responses to tuberculosis antigens but co-infections had little effect on cytokine responses. Exploring other risk factors, Th1 cytokines among LTBI-positive HHCs with BCG scars were greatly reduced compared to those without scars: (adjusted geometric mean ratio) IFNγ 0.20 (0.09-0.42), <0.0001; IL-2 0.34 (0.20-0.59), <0.0001; and TNFα 0.36 (0.16-0.79), 0.01.

CONCLUSIONS

We found no evidence that co-infections increase the risk of LTBI, or influence the cytokine response profile among those with LTBI. Prior BCG exposure may reduce Th1 cytokine responses in LTBI.

Strong decrease in streptomycin-resistance and absence of XDR 12 years after the Reorganization of the National Tuberculosis Control Program in the Central Region of Cameroon

Background

In the 1990s, resistance rates of 15% for streptomycin-resistance and 0.6% for multidrug-resistance (MDR) were reported from the Central Region of Cameroon. This work assesses drug resistant tuberculosis in this region 12 years after reorganization of the National Tuberculosis Control Program (NTCP).

Methods

This cross-sectional study was conducted from April 2010 to March 2011 in Jamot Hospital in Yaoundé, Cameroon. Only patients with smear positive pulmonary tuberculosis were included. Sputa were cultured and subsequently underwent drug susceptibility testing (DST). All consenting individuals were tested for their HIV status.

Results

A total of 665 smear positive pulmonary tuberculosis patients were enrolled. The HIV prevalence was 28.5% (95%CI [25.2–32.1]). Of the 582 sputa that grew Mycobacterium tuberculosis complex species, DST results were obtained for 576. The overall resistance rate was 10.9% (63/576). The overall resistance rates for single drug resistance were: isoniazid-resistance 4.7% (27/576), streptomycin-resistance 3.3% (19/576), rifampicin-resistance 0.2% (1/576), kanamycin-resistance 0.2% (1/576) and ofloxacin-resistance 0.2% (1/576). The MDR rate was 1.1% (6/576) and no extensively drug resistant tuberculosis (XDR) was detected.

Conclusions

The data show that reorganization of the NTCP resulted in a strong decrease in streptomycin-resistance and suggest that it prevented the emergence of XDR in the Central Region of Cameroon.

Sequence analysis for detection of drug resistance in Mycobacterium tuberculosis complex isolates from the Central Region of Cameroon

Background

The potential of genetic testing to rapidly diagnose drug resistance has lead to the development of new diagnostic assays. However, prior to implementation in a given setting, the association of specific mutations with specific drug resistance phenotypes should be evaluated. The purpose of this study was to evaluate molecular markers in predicting drug resistance in the Central Region of Cameroon.

Results

From April 2010 and March 2011, 725 smear positive pulmonary tuberculosis patients were enrolled and all positive cultures were tested for drug susceptibility. A total of 63 drug resistant and 100 drug sensitive Mycobacterium tuberculosis complex clinical isolates were screened for genetic mutations in katG, inhA, ahpC, rpoB, rpsL, rrs, gidB and embCAB loci using DNA sequencing. Of the 44 isoniazid resistant (INH^R) isolates (24 high level, 1 μg/ml and 20 low level, 0.2 μg/ml), 73% (32/44) carried the katG315 and/or the -15 inhA promoter mutations. Of the 24 high level INH^R, 17 (70.8%) harbored katG315 mutation, 1 a point mutation (-15C → T) in the inhA promoter and 6 were (25.0%) wild types. Thus, for INH^R high level detection, katG315 mutation had a specificity and a sensitivity of 100% and 70.8% respectively. Of the 20 low level INH^R, 10 (50.0%) had a -15C → T mutation in the inhA promoter region, and 1 (2.2%) a -32G → A mutation in the ahpC promoter region. All of the 7 rifampicin resistant (RIF^R) isolates carried mutations in the rpoB gene (at codons Ser531Leu (71.4%), His526Asp (14.3%), and Asp516Val (14.3%)). Of the 27 streptomycin resistant (SM^R) isolates, 7 carried mutations at the rpsL and the gidB genes. 1 of the 2 ethambutol resistant (EMB^R) isolates displayed a mutation in embB gene.

Conclusion

This study provided the first molecular investigation assessing the correlation of phenotypic to genotypic characteristics on MTB isolates from the Central Region of Cameroon using DNA sequencing. Mutations on rpoB, katG315 and -15 point mutations in inhA promoter loci could be used as markers for RIF and INH -resistance detection respectively.

Factors Influencing Sputum Conversion among Smear-Positive Pulmonary Tuberculosis Patients in Morocco

Background. Sputum smear-positive pulmonary tuberculosis patients expel infectious viable bacilli for a period following the commencement of treatment. Objective. To determine the time to sputum smear conversion and study the factors influencing it. Design. A prospective study was undertaken at our hospital in Rabat over a six-month period on a cohort of 119 sputum smear positive patients. Patients were followed up fortnightly. At each followup, specimens were collected and processed for microscopy using standard protocol. Results. 96.6% of our patients completed the study (4 deaths). Sputum conversion rate was 42% after two weeks, 73% after one month, and 95% after two months. Univariate and stepwise regression analysis showed that patients who had high smear grading, miliary, and bilateral radiologic lesions were more likely to undergo delayed sputum conversion (P<0.05). Other factors were thought to influence sputum conversion but were not statistically proven in our study. Conclusion. Since viable bacilli continue to be expelled for up to two months, infection control measures should be maintained for such a time. Patients with high smear grading, miliary, and bilateral radiologic lesions need to be monitored more closely.

Contact investigation for tuberculosis: a systematic review and meta-analysis

Investigation of contacts of patients with tuberculosis (TB) is a priority for TB control in high-income countries, and is increasingly being considered in resource-limited settings. This review was commissioned for a World Health Organization Expert Panel to develop global contact investigation guidelines. We performed a systematic review and meta-analysis of all studies reporting the prevalence of TB and latent TB infection, and the annual incidence of TB among contacts of patients with TB. After screening 9,555 titles, we included 203 published studies. In 95 studies from low- and middle-income settings, the prevalence of active TB in all contacts was 3.1% (95% CI 2.2-4.4%, I(2)=99.4%), microbiologically proven TB was 1.2% (95% CI 0.9-1.8%, I(2)=95.9%), and latent TB infection was 51.5% (95% CI 47.1-55.8%, I(2)=98.9%). The prevalence of TB among household contacts was 3.1% (95% CI 2.1-4.5%, I(2)=98.8%) and among contacts of patients with multidrug-resistant or extensively drug-resistant TB was 3.4% (95% CI 0.8-12.6%, I(2)=95.7%). Incidence was greatest in the first year after exposure. In 108 studies from high-income settings, the prevalence of TB among contacts was 1.4% (95% CI 1.1-1.8%, I(2)=98.7%), and the prevalence of latent infection was 28.1% (95% CI 24.2-32.4%, I(2)=99.5%). There was substantial heterogeneity among published studies. Contacts of TB patients are a high-risk group for developing TB, particularly within the first year. Children <5 yrs of age and people living with HIV are particularly at risk. Policy recommendations must consider evidence of the cost-effectiveness of various contact tracing strategies, and also incorporate complementary strategies to enhance case finding.

Modeling the dynamic relationship between HIV and the risk of drug-resistant tuberculosis

The emergence of highly drug-resistant tuberculosis (TB) and interactions between TB and HIV epidemics pose serious challenges for TB control. Previous researchers have presented several hypotheses for why HIV-coinfected TB patients may suffer an increased risk of drug-resistant TB (DRTB) compared to other TB patients. Although some studies have found a positive association between an individual's HIV status and his or her subsequent risk of multidrug-resistant TB (MDRTB), the observed individual-level relationship between HIV and DRTB varies substantially among settings. Here, we develop a modeling framework to explore the effect of HIV on the dynamics of DRTB. The model captures the acquisition of resistance to important classes of TB drugs, imposes fitness costs associated with resistance-conferring mutations, and allows for subsequent restoration of fitness because of compensatory mutations. Despite uncertainty in several key parameters, we demonstrate epidemic behavior that is robust over a range of assumptions. Whereas HIV facilitates the emergence of MDRTB within a community over several decades, HIV-seropositive individuals presenting with TB may, counterintuitively, be at lower risk of drug-resistant TB at early stages of the co-epidemic. This situation arises because many individuals with incident HIV infection will already harbor latent Mycobacterium tuberculosis infection acquired at an earlier time when drug resistance was less prevalent. We find that the rise of HIV can increase the prevalence of MDRTB within populations even as it lowers the average fitness of circulating MDRTB strains compared to similar populations unaffected by HIV. Preferential social mixing among individuals with similar HIV status and lower average CD4 counts among HIV-seropositive individuals further increase the expected burden of MDRTB. This model suggests that the individual-level association between HIV and drug-resistant forms of TB is dynamic, and therefore, cross-sectional studies that do not report a positive individual-level association will not provide assurance that HIV does not exacerbate the burden of resistant TB in the community.

Tuberculosis transmission attributable to close contacts and HIV status, Malawi

In this population, ≈90% of M. tuberculosis infections were transmitted by casual contact, and nearly half from HIV-positive patients.

We conducted the first molecular study of tuberculosis (TB) to estimate the role of household contact and transmission from HIV-positive putative source contacts (PSCs) in a high HIV-prevalence area. TB patients in a long-term population-based study in Malawi were asked about past contact with TB. DNA fingerprinting was used to define clusters of cases with identical strains. Among 143 epidemiologically defined PSC-case pairs, fingerprinting confirmed transmission for 44% of household and family contacts and 18% of other contacts. Transmission was less likely to be confirmed if the PSC were HIV positive than if he or she was HIV negative (odds ratio 0.32, 95% confidence interval [CI] 0.14–0.74). Overall, epidemiologic links were found for 11% of 754 fingerprint-clustered cases. We estimate that 9%–13% of TB cases were attributable to recent transmission from identifiable close contacts and that nearly half of the TB cases arising from recent infection had acquired the infection from HIV-positive patients.

The impact of the HIV epidemic on tuberculosis transmission in Tanzania

OBJECTIVE

To assess the impact of the HIV epidemic on tuberculosis transmission in Tanzania by estimating the trend in annual risk of tuberculosis infection (ARTI) over the period 1983-2003.

DESIGN

Tuberculin survey among school children aged 6-14 years, randomly selected by cluster sampling.

METHODS

Primary outcome was the ARTI among children without a BCG vaccination scar. To obtain time trends, data were reanalysed from three previous surveys carried out at intervals of 5 years since 1983, using identical methods and definitions.

RESULTS

Of 96,226 children included in the analysis (74% of those enrolled), 10,239 (11%) had no BCG scar. The ARTI was 0.68% (95% confidence interval 0.55-0.81). Despite a doubling of notification rates of smear-positive tuberculosis since 1983, this represents an average annual decline since the first survey of 2.7% (P < 0.001). The declining trend in ARTI was observed in 17 of 20 regions, with no association between this trend and region-specific prevalence of HIV infection among patients with tuberculosis (P = 0.575). A similar decline in ARTI was observed among children with a BCG scar and for various ways of estimating the prevalence of tuberculosis infection from the distribution of skin test reactions.

CONCLUSION

Despite substantial increases in tuberculosis incidence, the overall population-level effect of the HIV epidemic on tuberculosis transmission in Tanzania has been limited. This suggests that in the presence of a strong control programme, the HIV epidemic has limited impact on tuberculosis transmission.

Number of negative acid-fast smears needed to adequately assess infectivity of patients with pulmonary tuberculosis

STUDY OBJECTIVES

To investigate the relationship between the number of negative acid-fast bacilli (AFB) smear results and infectivity of pulmonary tuberculosis (TB).

DESIGN

Retrospective analysis.

METHODS AND SUBJECTS

We examined 122 index cases in Harris County, TX, reported in 1998 and 1999. All cases had only negative AFB smear results during the infectious period and were categorized in two groups: group A consisted of cases with only one or two sputum specimens collected and processed, and group B consisted of cases with at least three sputum specimens or at least one bronchoscopic specimen. Tuberculin skin test (TST) results of contacts were ascertained from the results of contact investigations performed by the City of Houston Department of Health and Human Services, Tuberculosis Control Division. Univariate and multivariate analyses were done to explore index case and contact attributes associated with tuberculosis (TB) transmission using positive TST results of contacts as a measure of recent transmission.

RESULTS

We found male gender and younger age of index cases along with Hispanic ethnicity of contacts to be independently associated with positive TST results, while younger contacts were less likely to be TST positive. Smear category of the index case (group A vs group B) was not independently associated with transmission. We also found that the first two sputum specimens in cases where three or more were performed yielded 90% of all positive culture results for Mycobacterium tuberculosis (MTB).

CONCLUSIONS

We conclude that two sputum specimens negative for AFB stain are adequate for both assessing infectivity and for isolating MTB from patients with pulmonary TB.

The impact of HIV/AIDS on the control of tuberculosis in India

Epidemics of HIV/AIDS have increased the tuberculosis (TB) case-load by five or more times in East Africa and southern Africa. As HIV continues to spread, warnings have been issued of disastrous AIDS and TB epidemics in "new-wave" countries, including India, which accounts for 20% of all new TB cases arising in the world each year. Here we investigate whether, in the face of the HIV epidemic, India's Revised National TB Control Program (RNTCP) could halve TB prevalence and death rates in the period 1990-2015, as specified by the United Nations Millennium Development Goals. Using a mathematical model to capture the spatial and temporal variation in TB and HIV in India, we predict that, without the RNTCP, HIV would increase TB prevalence (by 1%), incidence (by 12%), and mortality rates (by 33%) between 1990 and 2015. With the RNTCP, however, we expect substantial reductions in prevalence (by 68%), incidence (by 41%), and mortality (by 39%) between 1990 and 2015. In India, 29% of adults but 72% of HIV-positive adults live in four large states in the south where, even with the RNTCP, mortality is expected to fall by only 15% between 1990 and 2015. Nationally, the RNTCP should be able to reverse the increases in TB burden due to HIV but, to ensure that TB mortality is reduced by 50% or more by 2015, HIV-infected TB patients should be provided with antiretroviral therapy in addition to the recommended treatment for TB.

Understanding tuberculosis epidemiology using structured statistical models

Molecular epidemiological studies can provide novel insights into the transmission of infectious diseases such as tuberculosis. Typically, risk factors for transmission are identified using traditional hypothesis-driven statistical methods such as logistic regression. However, limitations become apparent in these approaches as the scope of these studies expand to include additional epidemiological and bacterial genomic data. Here we examine the use of Bayesian models to analyze tuberculosis epidemiology. We begin by exploring the use of Bayesian networks (BNs) to identify the distribution of tuberculosis patient attributes (including demographic and clinical attributes). Using existing algorithms for constructing BNs from observational data, we learned a BN from data about tuberculosis patients collected in San Francisco from 1991 to 1999. We verified that the resulting probabilistic models did in fact capture known statistical relationships. Next, we examine the use of newly introduced methods for representing and automatically constructing probabilistic models in structured domains. We use statistical relational models (SRMs) to model distributions over relational domains. SRMs are ideally suited to richly structured epidemiological data. We use a data-driven method to construct a statistical relational model directly from data stored in a relational database. The resulting model reveals the relationships between variables in the data and describes their distribution. We applied this procedure to the data on tuberculosis patients in San Francisco from 1991 to 1999, their Mycobacterium tuberculosis strains, and data on contact investigations. The resulting statistical relational model corroborated previously reported findings and revealed several novel associations. These models illustrate the potential for this approach to reveal relationships within richly structured data that may not be apparent using conventional statistical approaches. We show that Bayesian methods, in particular statistical relational models, are an important tool for understanding infectious disease epidemiology.

Factores asociados a la infección tuberculosa latente en los contactos de pacientes afectados

BACKGROUND

As tuberculosis control programs have reached acceptable levels in the identification and treatment of persons with active tuberculosis, the next step should be to develop methods of preventing new cases. Persons with latent tuberculosis infection (LTI) are considered to have a higher risk of developing active tuberculosis. The objective of this study was to evaluate the prevalence of LTI and its associated factors in the contacts of tuberculosis patients.

METHODS

We studied the contacts of tuberculosis patients who were examined in the Center for Tuberculosis Control and Prevention in Lleida (Spain) from 1991-1997. Factors associated with the index case (demographic, radiographic, bacteriologic and therapeutic) and tuberculin skin test results and demographic data in contacts were collected. Data on HIV infection, injection drug use and alcohol consumption in tuberculosis patients were also collected. The associations were assessed by obtaining crude and adjusted odds ratios.

RESULTS

The prevalence of LTI among contacts was 36.1% (780/2,161). In the multivariate analysis a higher frequency of LTI was detected in contacts older than 14 years (ORa = 3.34; 95% CI, 2.51-4.45), contacts who had a higher degree of exposure to the index case (ORa = 1.96; 95% CI, 1.59-2.42), contacts of pulmonary tuberculosis patients (ORa = 1.54; 95% CI, 1.01-2.35), contacts of patients with a positive sputum smear (ORa = 1.51; 95% CI, 1.15-1.99), contacts of patients with caverns on chest x-ray (ORa = 1.27; 95% CI, 1.01-1.61) and contacts of patients with delayed treatment (ORa = 1.31; 95% CI, 1.05-1.62).

CONCLUSIONS

The overall prevalence of LTI in the contacts of patients with tuberculosis was high. Among the factors studied, delayed treatment in the index case was independently associated with the frequency of LTI in tuberculosis contacts. Measures for the early diagnosis and treatment of tuberculosis should be intensified.

Survival of patients with pulmonary tuberculosis: clinical and molecular epidemiologic factors

Using restriction fragment-length polymorphism data, we conducted a retrospective cohort study of 139 adult patients with pulmonary tuberculosis to investigate the clinical impact of Mycobacterium tuberculosis infection with a clustered isolate. The cumulative all-cause mortality rate during treatment was 21%. Patients with clustered DNA fingerprint patterns had a reduced risk of death, compared with patients with unique patterns (hazard ratio [HR], 0.5; 95% confidence interval [CI], 0.2-1.1), but this finding was confounded by age (adjusted HR, 0.8; 95% CI, 0.4-1.8). After adjustment for age, the strongest predictors of death were such underlying illnesses as diabetes mellitus, renal failure, chronic obstructive pulmonary disease, and human immunodeficiency virus infection. We conclude that comorbidity and immunosuppression are important predictors of survival for patients with pulmonary tuberculosis in an inner-city cohort. Recently transmitted infection, as determined by use of DNA fingerprinting to classify patients' isolates as being either clustered or unique, was not independently associated with death.

Transmission of Mycobacterium tuberculosis to contacts of HIV-infected tuberculosis patients

We assessed the infectiousness of human immunodeficiency virus (HIV)-seropositive and HIV-seronegative individuals with pulmonary tuberculosis (TB) in a prospective cohort study. We enrolled, evaluated, and followed 104 close contacts of HIV-seropositive pulmonary TB patients and 256 close contacts of HIV-seronegative pulmonary TB patients using a standardized questionnaire, symptom review, chest radiograph, HIV serology, and tuberculin skin testing (TST). Contacts were followed for > or = 12 mo. TB infection at enrollment was 27% (28/104) among contacts of HIV-seropositive TB patients and 35% (90/256) among contacts of HIV-seronegative TB patients (odds ratio [OR] = 0.68, 95% confidence interval [CI] 0.41 to 1.12; p = 0.130). TST conversion occurred in 21% (42/ 204) of subjects; 8% (5/63) of contacts of HIV-seropositive index cases and 26% (37/141) of contacts of HIV-seronegative index cases (OR = 0.24, 95% CI 0.09 to 0.65; p = 0.003). TB was diagnosed in nine contacts; eight were contacts of HIV-seronegative index cases. HIV seropositivity in the index case was independently associated with a lower risk of TB infection among contacts, even among household contacts younger than 15 yr of age. Contacts of HIV-seropositive persons with pulmonary TB were less likely to have a positive TST response at 1 yr of follow-up than contacts of HIV-seronegative persons.

Amplification dynamics: predicting the effect of HIV on tuberculosis outbreaks

HIV affects the pathogenesis and the transmission of Mycobacterium tuberculosis. We used a discrete event simulation model to predict the potential impact of HIV on increasing the probability and the expected severity of tuberculosis outbreaks. Our predictions reveal that an HIV epidemic can significantly increase the frequency and severity of tuberculosis outbreaks, but that this amplification effect of HIV on tuberculosis outbreaks is very sensitive to the tuberculosis treatment rate. At moderate or low treatment rates, even a moderate HIV epidemic can cause the average size of tuberculosis outbreaks to almost double in comparison with the expected outbreak size when HIV is absent. However, we determined that the amplification effect of HIV can be substantially reduced if the treatment rate of tuberculosis is very high. We discuss the significant implications of these results for the global control of tuberculosis. Our results also reveal that occasionally a "normal-virulence" strain of M. tuberculosis can be expected to generate a large outbreak. We discuss the implications of these results in understanding the virulence of M. tuberculosis and in the planned elimination of tuberculosis in the United States.

The impact of human immunodeficiency virus type 1 on infectiousness of tuberculosis: a meta-analysis

To assess if the relative infectiousness of patients with tuberculosis is enhanced by coinfection with human immunodeficiency virus type 1 (HIV-1), data from 6 studies of 1240 health care workers who had contact with tuberculosis patients were analyzed. Overall rates of tuberculin skin test conversion were similar regardless of HIV-1 positivity of tuberculosis patients (odds ratio [OR], 1.04; 95% confidence interval [CI], 0.23-1.84). However, when only 3 studies during nosocomial outbreaks of multidrug-resistant Mycobacterium tuberculosis were analyzed, rates of skin test conversion were higher among contacts of HIV-1-positive index cases (OR, 2.85; 95% CI, 1.85-3.85; P=.0002). A second meta-analysis included data from 11 studies of 10,714 household contacts of tuberculosis patients. Prevalence of both skin test positivity (OR, 0.45; 95% CI, 0.20-1.03) and active disease (OR, 1.17; 95% CI, 0.78-1.56) were similar regardless of HIV-1 positivity of index cases. These data suggest that tuberculosis patients with HIV-1 infection are not intrinsically more infectious to their contacts than are HIV-1-negative tuberculosis patients.

[Risk factors associated to tuberculosis patients with positive sputum microscopy]

OBJECTIVE

The main factor responsible for producing new cases of tuberculosis by exogen transmission is the existence of Mycobacterium tuberculosis in the sputum of tuberculosis patients. The objective of this study was to determine the risk factors associated to positive smear tuberculosis cases in Lleida (Spain).

METHODS

We studied new cases of tuberculosis over the period 1992-1998. The variables considered were: age, gender, coinfection with HIV, injection drug use (IDU), consumption of alcohol, existence of caverns in thorax X-ray, and laboratory results of direct smear examination. We calculated the incidence rates for 100,000 persons-year. The association between the dependent variable case of tuberculosis with positive Mycobacterium tuberculosis smear and the remaining independent variables were assessed obtaining odds ratios (OR) and 95% confidence intervals (CI) (crude cOR and adjusted aOR by non conditional logistic regression).

RESULTS

We detected 905 new cases of tuberculosis. The rates in the period 1992-1998 decreased from 38.8 to 30.8. 44.9% of cases (n = 406) presented a positive direct smear. There was a positive association between the risk of being a positive smear patient and having caverns in thorax x-ray (aOR = 6.8; 95% CI, 4.8-95), being male (aOR = 1.8; 95% CI, 1.3-2.6) and consuming alcohol (aOR = 1.6; 95% CI,1.1-2.3) and this risk was significant lower in those under 15 years old (aOR = 0.2; 95% CI, 0.1-0.5), and coinfection with HIV (aOR = 0.5; 95% CI, 0.3-0.9).

CONCLUSIONS

HIV infection implies a reduced impact in endemecity of tuberculosis. Study of contacts and the implementation of directly observed treatment must be considered not only for coinfected HIV cases and IDU but also for adult males, especially those who consume alcohol, particularly when they have caverns.

[Tuberculosis notification from 1987 to 1999 for the public health area of the community of Valencia (Spain)]

OBJECTIVE

Under notification of tuberculosis (TB) is common worldwide but has hardly been studied in Spain. The objective of this study was to determine how many cases of TB are reported in our health care area.

MATERIAL AND METHOD

Between 1987 and 1999 we carried out a direct study of the incidence and reporting of TB cases in our area (106,632 inhabitants on the census). Cases were taken from mandatory notification, pathology and bacteriology files and were then reviewed.

RESULTS

Of the 410 TB cases diagnosed, 378 were residents of the area (annual incidence: 27/100,000 inhabitants), 223 of whom were reported (54%). Forty-eight patients were under 15 years of age. Sixty-seven percent of the pediatric cases and 53% of the adult cases were reported (n.s.). Of the 78 cases with HIV co-infection, only 32% were reported, in contrast with 60% of HIV-negative cases (p < 0.001). Of the 300 cases with pulmonary involvement, 56% were reported, versus 50% of those with exclusively extrapulmonary involvement (n.s.). For the 149 with positive Ziehl-Neelsen stain, 61% were reported, in contrast with 51% of those who were smear negative (n.s.). Diagnosis was based on clinical signs in 65 cases (16%), 51% of which were reported, versus 55% of those in which diagnosis was based on bacteriology or histology consistent with TB (n.s.). Overall under notification tended to decrease during the study period (r = 0.73, p < 0.005). Under notification also tended to decrease for patients with pulmonary involvement (r = 0.83, p < 0.0001) and for those with positive Ziehl-Neelsen staining of sputum (r = 0.79, p< 0.001). Likewise, under notification also decreased for HIV negative patients (r = 0.74, p < 0.02) but not significantly so for HIV positive patients r = 0.44, n.s.).

CONCLUSIONS

Direct quantification of cases revealed a significant degree of under notification that is tending to decrease. Under notification is greatest for HIV-positive patients and is not changing. No differences were seen for smear positive and smear negative patients, by pulmonary or extra-pulmonary involvement, for clinical versus laboratory diagnosis, or for patients who were younger or older than 15 years of age. Reporting should be improved so that measures to decrease the incidence of TB can be taken.

Adult tuberculosis in the 21st century: pathogenesis, clinical features, and management

This article reviews the significant advances in the past year in the basic and clinical aspects of adult tuberculosis (TB). Further research has deepened our understanding of host susceptibility and resistance mechanisms, including cytotoxicity, apoptosis, and antimicrobial polypeptides such as granulysin. Studies have confirmed the effects of HIV infection on risk of disease and disease manifestations, and have defined the effects of HIV on TB transmission. Recent studies also indicate a possible role for extended treatment of active disease and latent infection in HIV-1 infected individuals. Multidrug-resistant disease has been reported on every continent; rapid molecular approaches to the simultaneous diagnosis of TB and detection of rifampin resistance may facilitate prompt initiation of treatment. TB remains one of the major problems in global health.

The contribution of recently acquired Mycobacterium tuberculosis infection to the New York City tuberculosis epidemic, 1989-1993

Current theory in the molecular epidemiology of tuberculosis holds that tuberculosis cases harboring Mycobacterium tuberculosis strains with a common deoxyribonucleic acid (DNA) fingerprint are the result of recent M. tuberculosis transmission. Here we propose a mathematical approach independent of DNA fingerprinting to estimating the percentage of recent transmissions responsible for current tuberculosis incidence. The "short-term reproductive number" of tuberculosis is defined as the average number of tuberculosis cases developing within 1 year of infection. Multiplying the short-term reproductive number by the number of tuberculosis cases in each year and dividing by the subsequent year's tuberculosis case burden equals the proportion of tuberculosis cases in the subsequent year that are due to recent transmission. We carried out separate calculations for human immunodeficiency virus (HIV)-negative and HIV-positive tuberculosis cases. We applied the model to pulmonary (infectious) tuberculosis cases diagnosed in New York City during 1989-1993, using tuberculosis and AIDS surveillance data. Model-based estimates of the proportion of tuberculosis due to recent transmission were lower than estimates based on DNA fingerprints. Reconciliation of these divergent estimates may require the re-estimation of model parameters from data collected de novo, additional model development, and further advances in DNA fingerprinting methods.

Infectiousness of Mycobacterium tuberculosis in HIV-1-infected patients with tuberculosis: a prospective study

BACKGROUND

Previous studies concerning the relative infectiousness of HIV-1-positive individuals with pulmonary tuberculosis have produced conflicting results. Thus, we assessed the effect of HIV-1 on the infectiousness of Mycobacterium tuberculosis in a prospective study.

METHODS

We organised in Santo Domingo, Dominican Republic, a cohort study of household contacts of HIV-1-positive and HIV-1-negative individuals with newly diagnosed pulmonary tuberculosis. Household contacts were assessed at their houses at baseline and followed up for 14 months for evidence of M tuberculosis infection and tuberculosis with a multi-step tuberculin skin test, anergy skin test, physical examinations, chest radiographs, and sputum smears.

FINDINGS

Tuberculin induration of 5 mm or greater was seen in 153 (61%) of 252 household contacts of HIV-1-positive index cases and in 418 (76%) of 551 household contacts of HIV-1-negative index cases (odds ratio 0.49 [95% CI 0.35-0.67], p=0.00001). In multivariate logistic-regression analysis after allowance for between-household variation in tuberculin response, HIV-1 infection of the index case remained inversely associated with the tuberculin response of the household contacts (0.52 [0.29-0.93], p=0.02). When the analysis was restricted to household contacts aged between 2 years and 15 years the adjusted association remained significant (0.37 [0.14-0.98], p=0.04). Among household contacts who had a negative tuberculin skin test at baseline, conversion to tuberculin skin test positivity was less frequent among household contacts of HIV-1-positive index cases (cut-off > or =5 mm: 32/131 [24%] vs 71/204 [35%], p=0.05; cut-off > or =10 mm: 23/153 [15%] vs 55/245 [22%], p=0.07).

INTERPRETATION

These data suggest that HIV-1-positive individuals with tuberculosis are less likely than HIV-1-negative individuals with tuberculosis to transmit M tuberculosis to their close contacts. No changes in the current policy regarding tuberculosis contact tracing are needed in the presence of HIV-1.

How does tuberculosis relate to HIV positive and HIV negative drug users?

OBJECTIVES

(1) To compare the incidence of active tuberculosis in HIV positive and HIV negative drug users. (2) To describe the main characteristics of the tuberculosis cases.

DESIGN

A prospective study was performed from 1986 to 1996 as part of an ongoing cohort study of HIV infection in Amsterdam drug users.

METHODS

Data from the cohort study, including HIV serostatus and CD4-cell numbers, were completed with data from the tuberculosis registration of the tuberculosis department of the Amsterdam Municipal Health Service. Analyses were carried out with person time and survival methods.

RESULTS

Of 872 participants, 24 persons developed culture confirmed tuberculosis during a total follow up period of 4000 person years (0.60 per 100 py, 95% CI: 0.40, 0.90). Nineteen cases were HIV positive (1.54 per 100 py, 95% CI: 0.86, 2.11) and five HIV negative (0.18 per 100 py, 95% CI: 0.08, 0.43). Multivariately HIV infection (relative risk: 12.9; 95% CI: 3.4, 48.8) and age above 33 years (RR: 6.8; 95% CI: 1.3, 35.0, as compared with age below 27) increased the risk for tuberculosis substantially. Additional findings were: (1) 13 of 22 pulmonary tuberculosis cases (59%) were detected by half yearly radiographic screening of the chest; (2) tuberculosis occurred relatively early in the course of HIV infection at a mean CD4 cell number of 390/microliter; (3) an estimated two thirds of the incidence of tuberculosis observed among HIV positive cases was caused by reactivation; (4) all but one patient completed the tuberculosis treatment.

CONCLUSION

HIV infection increases the risk for active tuberculosis in Amsterdam drug users 13-fold. The incidence of tuberculosis in HIV negative drug users is still six times higher than in the overall Amsterdam population. In the absence of contact tracing and screening with tuberculin skin tests, periodic chest radiographic screening contributes substantially to early casefinding of active tuberculosis in Amsterdam drug users.

Consensus statement. Global burden of tuberculosis: estimated incidence, prevalence, and mortality by country. WHO Global Surveillance and Monitoring Project

OBJECTIVE

To estimate the risk and prevalence of Mycobacterium tuberculosis (MTB) infection and tuberculosis (TB) incidence, prevalence, and mortality, including disease attributable to human immunodeficiency virus (HIV), for 212 countries in 1997.

PARTICIPANTS

A panel of 86 TB experts and epidemiologists from more than 40 countries was chosen by the World Health Organization (WHO), with final agreement being reached between country experts and WHO staff.

EVIDENCE

Incidence of TB and mortality in each country was determined by (1) case notification to the WHO, (2) annual risk of infection data from tuberculin surveys, and (3) data on prevalence of smear-positive pulmonary disease from prevalence surveys. Estimates derived from relatively poor data were strongly influenced by panel member opinion. Objective estimates were derived from high-quality data collected recently by approved procedures.

CONSENSUS PROCESS

Agreement was reached by (1) participants reviewing methods and data and making provisional estimates in closed workshops held at WHO's 6 regional offices, (2) principal authors refining estimates using standard methods and all available data, and (3) country experts reviewing and adjusting these estimates and reaching final agreement with WHO staff.

CONCLUSIONS

In 1997, new cases of TB totaled an estimated 7.96 million (range, 6.3 million-11.1 million), including 3.52 million (2.8 million-4.9 million) cases (44%) of infectious pulmonary disease (smear-positive), and there were 16.2 million (12.1 million-22.5 million) existing cases of disease. An estimated 1.87 million (1.4 million-2.8 million) people died of TB and the global case fatality rate was 23% but exceeded 50% in some African countries with high HIV rates. Global prevalence of MTB infection was 32% (1.86 billion people). Eighty percent of all incident TB cases were found in 22 countries, with more than half the cases occurring in 5 Southeast Asian countries. Nine of 10 countries with the highest incidence rates per capita were in Africa. Prevalence of MTB/HIV coinfection worldwide was 0.18% and 640000 incident TB cases (8%) had HIV infection. The global burden of tuberculosis remains enormous, mainly because of poor control in Southeast Asia, sub-Saharan Africa, and eastern Europe, and because of high rates of M tuberculosis and HIV coinfection in some African countries.

Tuberculosis and the HIV epidemic: increasing annual risk of tuberculous infection in Kenya, 1986-1996

OBJECTIVES

The purpose of this study was to assess the impact of the increased incidence of tuberculosis (TB) due to HIV infection on the risk of TB infection in schoolchildren.

METHODS

Tuberculin surveys were carried out in randomly selected primary schools in 12 districts in Kenya during 1986 through 1990 and 1994 through 1996. Districts were grouped according to the year in which TB notification rates started to increase. HIV prevalence in TB patients and changes in TB infection prevalence were compared between districts.

RESULTS

Tuberculous infection prevalence rates increased strongly in districts where TB notification rates had increased before 1994 (odds ratio = 3.1, 95% confidence interval = 2.3, 4.1) but did not increase in districts where notification rates had increased more recently or not at all. HIV prevalence rates in TB patients were 50% in districts with an early increase in notification rates and 28% in the other study districts.

CONCLUSIONS

Countries with an increasing prevalence of HIV infection will need additional resources for TB control, not only for current patients but also for the patients in additional cases arising from the increased risk of TB infection.

Granulomatous inflammation and the transmission of infection: schistosomiasis--and TB too?

Immune-dependent granulomatous inflammation is important in the pathogenesis of both schistosomiasis and tuberculosis. A case has previously been made for a role for schistosome egg-induced granulomas in the onward transmission of infection. Here, Mike Doenhoff suggests that a similar hypothesis applies to tuberculosis.

Knowledge, Perceptions, and Practice of Nurses Toward HIV+/AIDS Patients Diagnosed With Tuberculosis

BACKGROUND

Tuberculosis (TB) continues to be a major health problem in the United States. Nurses may be exposed to TB and not realize their risks for becoming infected. The presentation of HIV-associated TB is somewhat different from "standard TB."

PURPOSE

The purpose of this study was to determine if an educational program could improve nurses' attitudes, level of knowledge, and compliance with infection control standards for HIV/AIDS patients diagnosed with TB.

METHOD

Participants included 50 staff nurses. The experimental group (35) and control group (15) completed a knowledge test and an attitude survey. Researchers observed participants for compliance with infection control standards pretest and posttest.

RESULTS

Following an educational program, the experimental group demonstrated a greater knowledge of TB than the control group who did not participate in the educational program (F [1.47] = 14.43, p = .000). In addition, the experimental group had a greater improvement in their Nursing Intervention Observation Tool adherence to respiratory isolation and universal precaution protocols scores as compared to the control group (F [1.47] = 8.95, p = .004). However, there was not a tangible increase in knowledge level of AIDS, attitudes or concerns about caring for these patients.

CONCLUSION

This nursing research study supports the need for an ongoing educational program with continual monitoring of infection control practices to positively affect client and caregiver outcomes.

Tuberculosis and human immunodeficiency virus infection

Mycobacterium tuberculosis infects one third of the world's population, and tuberculosis remains one of the most common infectious diseases of humans. From a global perspective, tuberculosis may be one of the most common HIV-related opportunistic infections. HIV immunosuppression has had a dramatic influence on the epidemiology, natural history and clinical presentation of tuberculosis. Treatment is highly effective for drug susceptible tuberculosis and has been shown to have a significant impact on resistant, especially multidrug-resistant, tuberculosis if started promptly. Directly observed therapy and rigorous adherence to infection control principles have helped control the tuberculosis epidemic in the United States.