Isoniazid preventive therapy for tuberculosis. Are we losing our enthusiasm?

Adverse reactions to first-line antituberculosis drugs

INTRODUCTION

Tuberculosis continues to be a major cause of morbidity and mortality worldwide. Currently available drugs are effective for treatment of the disease or latent infection, but may cause serious adverse effects.

METHODS

The authors reviewed the literature for side effects of five first-line antituberculous medications (isoniazid, rifampin, pyrazinamide, ethambutol and streptomycin). Incidence of the major side effects were compiled with particular attention to the incidence of isoniazid hepatotoxicity.

RESULTS

Hepatotoxicity to isoniazid is a serious problem. Although overall incidence may be decreasing, incidence averaged 9.2 per 1000 patients who were compliant, in multiple studies, with a case fatality rate of 4.7%. The incidence is higher with increasing age. Other serious adverse effects include dermatological, gastrointestinal, hypersensitivity, neurological, haematological and renal reactions. They can lead to drug discontinuation (in up to 10% of patients) or even more serious morbidity or mortality.

CONCLUSIONS

Side effects to antituberculosis drugs are common, and include hepatitis, cutaneous reactions, gastrointestinal intolerance, haematological reactions and renal failure. These adverse effects must be recognised early, to reduce associated morbidity and mortality.

Assessment of age-related isoniazid hepatotoxicity during treatment of latent tuberculosis infection

BACKGROUND

Since the introduction of new recommendations for the treatment of latent tuberculosis infection (LTB1) disregarding age as a limitation, increasing numbers of older individuals are expected to undergo treatment with isoniazid for the prevention of tuberculosis, raising the potential for an increase in isoniazid hepatotoxicity.

OBJECTIVE

To compare the frequency of hepatotoxicity requiring withdrawal of isoniazid therapy for LTB1 in patients under and over 35 years of age, managed according to current practice guidelines.

DESIGN

A retrospective analysis of 300 patients who underwent isoniazid therapy for LTB1 according to a protocol based on the current practice guidelines.

SETTING

Public health clinic of Passaic County, NJMain outcome measures: The frequency of symptomatic isoniazid hepatitis in various age groups.

RESULTS

Of 165 patients < 35 years of age, 3(2%) patients developed hepatitis (AST > 3 times the upper limit of normal). Of 135 patients > or = 35 years of age, 4(3%) patients developed hepatitis. Statistical comparison between the two groups failed to show a significant difference (p = 0.705).

CONCLUSIONS

No difference was detected in the frequency of isoniazid hepatotoxicity between patients < 35 and > or = 35 years of age. Clinically monitored isoniazid therapy of LTB1 patients > or = 35 years of age may not predispose subjects to an increased risk of hepatotoxicity. Limitations of this work include the small sample size and the retrospective nature of the study.

Guidelines of tuberculosis preventive therapy for HIV-infected persons: a prospective, multicentre study. GISTA (Gruppo Italiano di Studio Tubercolosi e AIDS)

The aim of this study was to assess the degree of implementation of national guidelines for isoniazid preventive therapy (IPT) among human immunodeficiency virus (HIV)-infected individuals and factors affecting the impact of the programme. Twenty-eight infectious disease hospital units in Italy participated in this observational, multicentre, prospective cohort study. A number of HIV-infected subjects, (n=1,705) seen for the first time as outpatients, were included in this analysis. Of the subjects considered, 1,215 out of the 1,705 completed purified protein derivative (PPD) screening. Variables independently associated with offering and completion of PPD screening included having acquired immune deficiency syndrome (AIDS), higher educational levels and currently receiving therapy. Overall, 103 subjects were identified as candidates for IPT. Of these subjects, five had tuberculosis and 15 had contraindications to IPT. Forty subjects agreed to start IPT, and 29 completed a full-course regimen. The incidence of tuberculosis among IPT candidates who either did not begin or discontinued IPT was 6.1 per 100 person-yrs, while no cases of tuberculosis were observed in subjects completing IPT. Several factors may limit the implementation of an isoniazid preventive therapy programme for human immunodeficiency virus-infected persons. Physicians fail to offer purified protein derivative screening to patients with high degrees of immunodeficiency, and those with a more intense workload seem to pay less attention to this test. The high number of contraindications among patients and their low level of acceptance further affects the impact of isoniazid preventive therapy.

The cost-effectiveness of evidence-based guidelines and practice for screening and prevention of tuberculosis

INTRODUCTION

The potential cost-effectiveness of screening depends on the risk of tuberculosis (TB) in the population being screened and the rate at which the screening outcome (prevention) is achieved.

AIMS

To compare the cost-effectiveness of contact screening for TB for: (1) contact screening as it actually occurred in Victoria in 1991 (Model 1); (2) the process which should have occurred had the 1991 contact screening guidelines been followed (Model 2); (3) a hypothetical evidence-based model (Model 3).

METHODS

Three models were constructed according to the aims. The cost-effectiveness of contact screening is presented as costs to government per unit outcome (in the form of cases prevented, cases found and contacts traced) for each model. Assumptions about disease behaviour were consistent between models. A sensitivity analysis was performed to examine the effect of the assumptions made in Model 3 about rates of referral and treatment of infected contacts, and about the efficacy of isoniazid (INH) in preventing TB.

RESULTS

The total cost of Model 1 was greater than that of the other Models. Model 1 is the least cost-effective, costing $309 065 per case prevented, and Model 3 is the most cost-effective, costing $32 210 per case prevented. The cost of Model 2 was $58 742 per case prevented. The incremental cost-effectiveness of Model 3 compared to Model 2 is $107 per additional contact screened, and $3881 per additional case prevented. Case finding is not as cost-effective as best-practice case prevention, ranging from $231 799 per case found in Model 1 to $205 596 per case found in Model 2. The sensitivity analysis shows that the cost-effectiveness of Model 3 decreases with lower referral rates, lower rates of preventive therapy, and lower efficacy of INH. However, even allowing for reduced programme parameters, Model 3 is most cost-effective.

DISCUSSION

Costing policy options is an important component of programme delivery, but needs to be considered in the context of the product being purchased, e.g. the prevention of disease, or case finding. Case finding as a product of contact screening is expensive in all three models. Prevention of TB, on the other hand, can be cost-effective, as shown in Model 3. It was least cost-effective in Model 1, largely because prevention was not considered a priority, and few infected contacts actually received preventive therapy. Clear programme aims, adherence to guidelines and high rates of preventive therapy are essential in order to achieve cost-effectiveness.

Tuberculosis in South-East Asian refugees after resettlement--can prevention be improved by better policy and practice?

OBJECTIVE

This study aimed to determine whether incident cases of tuberculosis (TB) in a cohort of South-East Asian refugees followed for 5 years after resettlement were potentially preventable and whether prevention of TB was optimal in a state refugee TB screening program in Victoria, Australia.

DESIGN

A retrospective cohort study of 1,101 refugees from Laos, Cambodia, and Vietnam screened for TB in the 6-month period from July 1989 to January 1990 was conducted. Incident cases of TB were identified by matching each refugee with the TB notification database for 5 years from the date of initial screening. Preventability was assessed for incident cases by reviewing medical records. Screening guidelines and practice were reviewed.

RESULTS

The main outcome was the preventability of cases of active tuberculosis that developed in the study population in the first 5 years after resettlement. The incidence of active TB was 363/100,000 during the first year and 109/100,000/year during the first 5 years. Five of six incident cases were assessed as potentially preventable, which if prevented would have resulted in an annual incidence of 18/100,000 over the first 5 years. Use of a more sensitive skin test definition of infection would have made an additional 245 refugees eligible for prevention and potentially prevented an additional 25 cases of TB over a lifetime.

CONCLUSIONS

There is a high incidence of tuberculosis among SE Asian refugees, particularly in the first year after resettlement. A large proportion of TB may be preventable. Improvement in case prevention may be possible with updated guidelines and better implementation of screening policy.

Impact of policy and practice on the effectiveness of contact screening for tuberculosis

BACKGROUND

Screening for tuberculosis is conducted because TB is a disease of public health importance that can be prevented if screening is followed by isoniazid prophylaxis for infected individuals. Screening alone is not effective unless that screening is rational and systematic and is followed by prevention where appropriate. Our aim was to consider whether the TB contact screening guidelines are evidence-based and appropriate, how well these guidelines are implemented, and how policy and practice impact on prevention.

METHODS

A cohort of 1,142 recent contacts screened in 1991 in Victoria, Australia, was studied. We evaluated the appropriateness of the screening guidelines and how well they were implemented and how the combination of these two factors impacted on the efficacy of the screening program.

RESULTS

The screening guidelines required updating and were not evidence-based. Chest radiograph (CXR) was overused and was the sole screening tool for nearly 40% (449/1,142) of contacts. Eighty percent of repeat CXRs were done following a normal initial study. Skin testing was underused. In nearly 60% (658/1,142) of all contacts, the presence or absence of infection could not be determined because a skin test was not done and the CXR, if done, was clear. Only 22% (38/175) of identified, eligible contacts received isoniazid preventive therapy.

CONCLUSIONS

Lack of evidence-based guidelines, as well as poor adherence to guidelines, resulted in an inefficient program. This problem may not be unique to the study setting, but cannot be identified without systematic program evaluation, for which we have provided a model.

Prevention and early detection of tuberculosis

1,570 subjects with known TB contacts (active TB, old TB and primary infection) and individuals with no known contacts but belonging to 'defined TB risk groups' were screened at the Department of Tuberculosis Prevention at the La Fe Hospital in Valencia. The total infection rate was 40.13% and active TBC was diagnosed in 2.23% of the population screened. Infection and disease rates were significant in all the groups examined, showing the need for correct screening not only for active TB contacts but also for child primary infection contacts, old TB cases not previously screened and subjects with no known contacts but belonging to a 'TB risk group'.

Underutilization of isoniazid chemoprophylaxis in tuberculosis contacts 50 years of age and older. A prospective analysis

STUDY OBJECTIVES

To examine the utilization of chemoprophylaxis for tuberculosis in certain high-risk groups, ie, infected contacts 50 years and older, and to study the safety of isoniazid (INH) preventive therapy in such persons.

DESIGN

From 1987 to 1992, two-part questionnaires were sent to each of the regional health offices within the 95 counties of Tennessee to document cases of purified protein derivative skin test conversion or reaction among close contacts of new patients with active tuberculosis. Infected contacts 50 years and older were included in the study.

METHODS

Data collected from these questionnaires were grouped according to age, sex, race, liver functions test (LFT), and whether chemotherapy was completed. Reasons for early discontinuation were also recorded. High values of LFTs were classified in the various groups as either twofold elevation or greater than threefold elevation.

RESULTS

Of the 829 responses for persons fitting the criteria for INH chemoprophylaxis, 415 began treatment; 249 (60%) of those completed the full course (9 months) and 166 stopped prematurely. Of the 414 persons (50%) who did not start preventive therapy, 233 (56.5%) respondents listed age as the reason. No patients started on a regimen of therapy developed hepatitis. Of those completing therapy, 6.9% had a rise in liver enzyme values but remained asymptomatic for hepatitis. Liver enzyme level elevation was significantly higher among patients who discontinued therapy, particularly white women, than those who completed the full course. Asymptomatic liver enzyme level elevation (> or = 3 times normal value), private practitioners' preferences, and patients arbitrarily stopping therapy were the leading reasons for incomplete INH preventive therapy.

CONCLUSION

We conclude that 30% of tuberculosis-infected contacts deserving chemoprophylaxis were actually provided the full benefit of INH preventive therapy, indicating underutilization of this prevention strategy, particularly in contacts older than 50 years.

Outbreak of tuberculosis in a church

A 48-year-old white man (index case) with an abnormal chest radiograph remained undiagnosed for tuberculosis for 4 years. Investigation by purified protein derivative (PPD) tuberculin test revealed positive tuberculin reactions (> or = 10 mm induration) in seven of eight (88%) initial close contacts, and in 12 of 46 (26%) coworkers. On the suspicion that transmission had also occurred among members of the index case's church congregation, a PPD tuberculin test survey of 184 of 200 of the members revealed 77 (42%) positive reactors. Thirty percent of the members under the age of 35 years were infected, suggesting transmission of infection. Eight cases of active tuberculosis (including the index case) were detected, yielding a high case rate (4.3%) among the parishioners. Three of the cases were confirmed recent PPD converters. Although bacteriologic findings were available in only three of the eight cases, two cases had phage typing of organism identical to the index case; the third had recrudescent tuberculous disease. Of the remaining five cases without bacteriologic confirmation, two had pleural tuberculosis, one child had progressive primary tuberculosis, and two persons had localized pulmonary nodules suggestive of primary infection progressing to disease. Because transmission of tuberculous infection may occur in any closed environment, including a church, physicians must be conversant with tuberculosis control measures and preventive therapy guidelines to preclude unforeseen transmission of disease.