Treatment as prevention and other interventions to reduce transmission of multidrug-resistant tuberculosis

Drug-resistant tuberculosis (DR-TB) represents a major programmatic challenge at the national and global levels. Only ∼30% of patients with multidrug-resistant TB (MDR-TB) were diagnosed, and ∼25% were initiated on treatment for MDR-TB in 2016. Increasing evidence now points towards primary transmission of DR-TB, rather than inadequate treatment, as the main driver of the DR-TB epidemic. The cornerstone of DR-TB transmission prevention should be earlier diagnosis and prompt initiation of effective treatment for all patients with DR-TB. Despite the extensive scale-up of Xpert^® MTB/RIF testing, major implementation barriers continue to limit its impact. Although there is longstanding evidence in support of the rapid impact of treatment on patient infectiousness, delays in the initiation of effective DR-TB treatment persist, resulting in ongoing transmission. However, it is also imperative to address the burden of latent drug-resistant tuberculous infection because it is estimated that many DR-TB patients will become infectious before seeking care and encounter various diagnostic delays before treatment. Addressing latent DR-TB primarily consists of identifying, treating and following the contacts of patients with MDR-TB, typically through household contact evaluation. Adjunctive measures, such as improved ventilation and use of germicidal ultraviolet technology can further reduce TB transmission in high-risk congregate settings. Although many gaps remain in our biological understanding of TB transmission, implementation barriers to early diagnosis and rapid initiation of effective DR-TB treatment can and must be overcome if we are to impact DR-TB incidence in the short and long term.

Droplets, dust and guinea pigs: an historical review of tuberculosis transmission research, 1878-1940

The transmission of tuberculosis (TB) occurs mainly via inhalation of airborne droplet nuclei; however, the precise details of this process remain uncertain. We reviewed the literature from 1870 to 1940, when Mycobacterium tuberculosis was discovered and the concept of transmission emerged as a hallmark of the infectious disease. By 1940, laboratory experiments, animal studies and clinical observation had demonstrated that cough was central to TB transmission, and that guinea pigs close to patients with cough could be infected, mainly by patients coughing small droplets likely containing only 1-2 bacilli. A minority of pulmonary TB patients, usually during the early stages of the disease, with thin watery sputum, more successfully coughed small infectious droplets than patients with heavily smear-positive tenacious sputum who were often too ill and too weak to cough vigorously. There was ongoing debate regarding the possible importance of desiccated sputum particles found in surface dust. Investigation of TB transmission has a history of more than 130 years.

FAST implementation in Bangladesh: high frequency of unsuspected tuberculosis justifies challenges of scale-up

SETTING

National Institute of Diseases of the Chest and Hospital, Dhaka; Bangladesh Institute of Research and Rehabilitation in Diabetes, Endocrine and Metabolic Disorders, Dhaka; and Chittagong Chest Disease Hospital, Chittagong, Bangladesh.

OBJECTIVE

To present operational data and discuss the challenges of implementing FAST (Find cases Actively, Separate safely and Treat effectively) as a tuberculosis (TB) transmission control strategy.

DESIGN

FAST was implemented sequentially at three hospitals.

RESULTS

Using Xpert® MTB/RIF, 733/6028 (12.2%, 95%CI 11.4-13.0) patients were diagnosed with unsuspected TB. Patients with a history of TB who were admitted with other lung diseases had more than twice the odds of being diagnosed with unsuspected TB as those with no history of TB (OR 2.6, 95%CI 2.2-3.0, P < 0.001). Unsuspected multidrug-resistant TB (MDR-TB) was diagnosed in 89/1415 patients (6.3%, 95%CI 5.1-7.7). Patients with unsuspected TB had nearly five times the odds of being diagnosed with MDR-TB than those admitted with a known TB diagnosis (OR 4.9, 95%CI 3.1-7.6, P < 0.001). Implementation challenges include staff shortages, diagnostic failure, supply-chain issues and reliance on external funding.

CONCLUSION

FAST implementation revealed a high frequency of unsuspected TB in hospitalized patients in Bangladesh. Patients with a previous history of TB have an increased risk of being diagnosed with unsuspected TB. Ensuring financial resources, stakeholder engagement and laboratory capacity are important for sustainability and scalability.

Rapid impact of effective treatment on transmission of multidrug-resistant tuberculosis

BACKGROUND

Effective treatment for drug-susceptible tuberculosis (TB) rapidly renders patients non-infectious, long before conversion of sputum acid-fast smear or culture to negative. Multidrug-resistant TB (MDR-TB) patients on treatment are currently assumed to remain infectious for months. While the resources required for prolonged hospitalization are a barrier to the scale-up of MDR-TB treatment, the safety of community treatment is clear.

OBJECTIVES

To estimate the impact of treatment on infectiousness among MDR-TB patients.

METHODS

A series of five human-to-guinea pig TB transmission studies was conducted to test various interventions for infection control. Guinea pigs in adjacent chambers were exposed to exhaust air from a hospital ward occupied by mostly sputum smear- and culture-positive MDR-TB patients. The guinea pigs then underwent tuberculin skin testing for infection. Only the control groups of guinea pigs from each study (no interventions used) provide the data for this analysis. The number of guinea pigs infected in each study is reported and correlated with Mycobacterium tuberculosis drug susceptibility relative to treatment.

RESULTS

Despite exposure to presumably infectious MDR-TB patients, infection percentages among guinea pigs ranged from 1% to 77% in the five experiments conducted. In one experiment in which guinea pigs were exposed to 27 MDR-TB patients newly started on effective treatment for 3 months, there was minimal transmission. In four other experiments with greater transmission, guinea pigs had been exposed to patients with unsuspected extensively drug-resistant tuberculosis who were not on effective treatment.

CONCLUSIONS

In this model, effective treatment appears to render MDR-TB patients rapidly non-infectious. Further prospective studies on this subject are needed.

Turning off the spigot: reducing drug-resistant tuberculosis transmission in resource-limited settings

Ongoing transmission and re-infection, primarily in congregate settings, is a key factor fueling the global multidrug-resistant/extensively drug-resistant tuberculosis (MDR/XDR-TB) epidemic, especially in association with the human immunodeficiency virus. Even as efforts to broadly implement conventional TB transmission control measures begin, current strategies may be incompletely effective under the overcrowded conditions extant in high-burden, resource-limited settings. Longstanding evidence suggesting that TB patients on effective therapy rapidly become non-infectious and that unsuspected, untreated TB cases account for the most transmission makes a strong case for the implementation of rapid point-of-care diagnostics coupled with fully supervised effective treatment. Among the most important decisions affecting transmission, the choice of an MDR-TB treatment model that includes community-based treatment may offer important advantages over hospital or clinic-based care, not only in cost and effectiveness, but also in transmission control. In the community, too, rapid identification of infectious cases, especially drug-resistant cases, followed by effective, fully supervised treatment, is critical to stopping transmission. Among the conventional interventions available, we present a simple triage and separation strategy, point out that separation is intimately linked to the design and engineering of clinical space and call attention to the pros and cons of natural ventilation, simple mechanical ventilation systems, germicidal ultraviolet air disinfection, fit-tested respirators on health care workers and short-term use of masks on patients before treatment is initiated.

Latent tuberculosis infection: risks to health care students at a hospital in Lima, Peru

SETTING

University hospital and university campus in Lima, Peru.

OBJECTIVE

To demonstrate the risk of latent tuberculosis infection (LTBI) in the hospital relative to the community.

DESIGN

Prospective cohort study of university students measuring prevalence, boosting, and conversion of tuberculin skin tests (TSTs) among health care students (HCS) and non-health care students (NHCS).

RESULTS

Among the HCS relative to NHCS, prevalence of initial positive TST was 20.9% vs. 12.2% (P < 0.001), and conversion rate was 1.1% vs. 0% (P = 0.423) at the 10 mm cut-off and 11.8% vs. 0% at the 6 mm cut-off (P = 0.00005). Multivariate analysis showed that the HCS group had a higher risk of baseline positive TST compared with the NHCS group after controlling for confounding factors (OR 1.7, 95% CI 1.1-2.6).

CONCLUSION

HCS are at greater risk than NHCS for having positive baseline TSTs and for TST conversion at the 6 mm cut-off. We conclude that the hospital we studied in Lima, Peru, poses a greater risk than the surrounding community for tuberculosis infection, and greater attention to hospital infection control measures is warranted. A higher rate of skin test boosting among the HCS cohort suggests the possibility of transient, non-progressive LTBI, which merits further study.

Clonal relationships in a shelter-associated outbreak of drug-resistant tuberculosis: 1983-1997

SETTING

An outbreak of tuberculosis caused by Mycobacterium tuberculosis resistant to isoniazid and streptomycin (HS-resistant) was documented in Boston's homeless population in 1984. Isolate relatedness was confirmed at the time by phage typing. In the late 1990s, cases of HS-resistant tuberculosis in the homeless were also documented, confirmed by RFLP typing using IS6110. None of the phage typed isolates from the 1980s were viable for performing RFLP analysis. We attempted to determine, using mixed-linker PCR (M-L PCR) finger-printing, whether or not these cases were all due to the same strain of M. tuberculosis.

DESIGN

Isolates from 10 HS-resistant patients-four non-viable isolates from the 1980s and six viable isolates from 1996-1997-were sent to the Centers for Disease Control and Prevention for M-L PCR fingerprinting. These results were combined with record reviews of older cases and an ongoing epidemiologic investigation.

RESULTS

Eight of 10 of the isolates were clonal, and the other two were strongly suspected matches. Epidemiologic investigation determined that transmission continued to occur after the initial outbreak in 1984-1985, and that a streptomycin-monoresistant variant of the strain was also circulating.

CONCLUSION

M-L PCR fingerprinting combined with epidemiology was able to document links between cases across 15 years.

Supplementing tuberculosis surveillance with automated data from health maintenance organizations

Data collected by health maintenance organizations (HMOs), which provide care for an increasing number of persons with tuberculosis (TB), may be used to complement traditional TB surveillance. We evaluated the ability of HMO-based surveillance to contribute to overall TB reporting through the use of routinely collected automated data for approximately 350,000 HMO members. During approximately 1.5 million person-years, 45 incident cases were identified in either HMO or public health department records. Eight (18%) confirmed cases had not been identified by the public health department. The most useful screening criterion (sensitivity of 89% and predictive value positive of 30%) was dispensing of two or more TB drugs. Pharmacy dispensing information routinely collected by many HMOs appears to be a useful adjunct to traditional TB surveillance, particularly for identifying cases without positive microbiologic results that may be missed by traditional public health surveillance methods.

Using automated pharmacy records to assess the management of tuberculosis

We used automated pharmacy dispensing data to characterize tuberculosis (TB) management for 45 health maintenance organization (HMO) members. Pharmacy records distinguished patients treated in HMOs from those treated elsewhere. For cases treated in HMOs, they provided useful information about appropriateness of prescribed regimens and adherence to therapy.

Supplementing tuberculosis surveillance with automated data from health maintenance organizations

Data collected by health maintenance organizations (HMOs), which provide care for an increasing number of persons with tuberculosis (TB), may be used to complement traditional TB surveillance. We evaluated the ability of HMO-based surveillance to contribute to overall TB reporting through the use of routinely collected automated data for approximately 350,000 HMO members. During approximately 1.5 million person-years, 45 incident cases were identified in either HMO or public health department records. Eight (18%) confirmed cases had not been identified by the public health department. The most useful screening criterion (sensitivity of 89% and predictive value positive of 30%) was dispensing of two or more TB drugs. Pharmacy dispensing information routinely collected by many HMOs appears to be a useful adjunct to traditional TB surveillance, particularly for identifying cases without positive microbiologic results that may be missed by traditional public health surveillance methods.

Long-term hospitalization for tuberculosis control. Experience with a medical-psychosocial inpatient unit

CONTEXT

Patients with tuberculosis (TB) who are nonadherent to therapy or have complicated medical or social problems pose a threat to public health. In some cases, hospitalization may be a necessary component of a comprehensive TB control program.

OBJECTIVE

To describe experience with a new inpatient program for TB control.

DESIGN

Retrospective review.

SETTING

Eighteen-bed, secure, TB treatment unit in a state public health hospital providing a spectrum of acute and chronic care services.

PATIENTS

Patients with known or suspected TB who were unable to be treated as outpatients and were hospitalized from 1990 through 1995.

INTERVENTIONS

Voluntary or involuntary hospitalization, with medical, psychosocial, and legal services.

MAIN OUTCOME MEASURES

Admissions, treatment completion, and disposition.

RESULTS

A total of 166 patients with a confirmed diagnosis of TB accounted for 214 hospitalizations for TB. The mean age was 42 years, 132 (79.5%) were men, 84 (50.6%) were nonwhite, and 45 (27.1%) were foreign born. At the time of admission, 58 patients (34.5%) were homeless, 116 (69.9%) had a history of abuse of alcohol or other drugs, and 46 (31.7%) were positive for human immunodeficiency virus. The mean length of stay was 119.7 days (median, 70 days; range, 7-656 days), and was higher among homeless patients than nonhomeless patients (168.8 vs 93.4 days). Of 48 patients (28.9%) who were admitted involuntarily, 21 required long-term confinement under court order. Admission indications (not mutually exclusive) changed over 5 years: nonadherence decreased (95% to 34%), medical complexity increased (14% to 77%), short-term isolation increased (19% to 39%), and involuntary admission decreased (54% to 13%). Of 157 patients with positive cultures for Mycobacterium tuberculosis, 36 (23.1%) were resistant to at least 1 drug, including 16 who were multidrug resistant. A total of 123 patients (74.7%) were discharged to an outpatient setting to complete therapy, 40 (24.1%) required inpatient care to complete therapy, and 3 died (1 from TB) before discharge.

CONCLUSIONS

A high proportion of patients with TB who failed outpatient therapy completed treatment in a combined medical and psychosocial inpatient unit. During the 5-year study period, involuntary admissions decreased and most patients completed therapy as outpatients. In Massachusetts, this program plays an important role in protecting public health and in providing specialized medical management for patients to complete therapy in a safe and supportive environment.

Exogenous reinfection with tuberculosis in a shelter for the homeless

We investigated an outbreak of tuberculosis in a large shelter for the homeless to assess the role of exogenous reinfection as opposed to reactivation of endogenous infection as the cause of secondary tuberculosis in this population. Exogenous reinfection is considered relatively unimportant in the United States and other developed countries. Of 49 shelter-related cases, 22 had cultures resistant to both isoniazid and streptomycin and of the same phage type, indicating recent transmission originating with a single index patient. The probable index patient had a 10-year history of isoniazid and streptomycin resistance--an uncommon pattern at the shelter during the three years preceding the outbreak. In 4 of the 22 cases, the patient had previously had documented tuberculosis infection or disease. These reinfected patients had extensive lung cavitation and numerous acid-fast bacilli on sputum smears--features associated with contagiousness. In contrast, patients with tuberculosis for the first time (primary tuberculosis) are usually less contagious. We conclude that exogenous reinfection may have been an important factor leading to highly contagious secondary cases and an acceleration of the usual pattern of tuberculosis transmission in this highly susceptible population.