Advance Notice of  Meetings :

TB Focus programme

Westminster and Chelsea Hospital, Fulham Rd 12/12/00

 2 pm to 5.15 pm

3 CME points applied for

Abstracts

In Malawi, sputum smear microscopy is the cornerstone of case finding and diagnosis in TB control activities. The advent of the HIV pandemic has been associated with a rise in the number of TB suspects and cases, resulting in increased workload to be dealt with by the same or even fewer numbers of laboratory staff. Maintaining quality is a considerable challenge. Issues relating to laboratory workload, human resources, quality control, costs and efficiency of the laboratory service will be presented and discussed. In Ntcheu District a simple internal quality control system, focusing on specimen suitability, smear preparation and microscopic examination of smears was piloted. Our experiences are currently being used to offer solutions to some of the problems and point the way forward for laboratory diagnosis of TB in Malawi and other low-income countries with similar problems.

Although annual incidence of tuberculosis in the U.S. decreased by 32% from 1992 to 6.4 per hundred thousand population in 1999, the "elimination" goal of less than 1 case per million population will not be reached by 2010. The Institute of Medicine (IOM) report on the elimination of tuberculosis recommends that once treatment of active cases is assured , the next step is to focus on prevention through testing of contacts and targeted testing of high risk groups New recommendations for the treatment of latent tuberculosis infection (LTBI), traditionally more common in the US than in many European countries, is outlined in the American Thoracic Society/Centers for Disease Control and Prevention guidelines "Targeted Tuberculin Testing and Treatment of Latent Tuberculosis Infection."

Isoniazid for 6-12 months has been recommended for infected contacts of active TB cases, and other infected individuals at high risk of recent infection, for over 30 years in the U.S. The recommendations were not uniformly followed because of the long duration of treatment, poor adherence, and concerns about toxicity. Results of recent studies of "short-course" treatment of LTBI, together with prior studies of isoniazid, provide the basis for new treatment guidelines. New regimens including two months of pyrazinamide + rifampicin, and four months of rifampicin alone, are recommended alternatives to isoniazid for nine months (preferred) or six months.

Tuberculin testing using Purified Protein Derivative (PPD) injected by the Mantoux technique is widespread in the U.S. To decrease the risk of false positives in a low-prevalence population, the definition of a positive reaction indicating infection was increased from > 10 mm induration to > 15 mm in individuals with little risk for recent infection or progression to active disease. For contacts of an active case, the > 10 mm induration definition remains; it is recommended that adult contacts with a positive reaction receive treatment for LTBI..

In 1999, foreign-born individuals made up 43% of the population with active tuberculosis; if current trends continue, the majority of cases will be foreign-born from 2002 onwards. Screening for and treatment of active disease before immigration has not led to a decline in the number of foreign-born cases. Targeted tuberculin testing of groups from countries with a high tuberculosis prevalence is becoming more common in many areas of the U.S. Treatment for LTBI is recommended for those with a > 10 mm reaction, regardless of BCG status. The IOM report suggests that measures requiring substantial additional resources, including tuberculin screening before immigration, should be put in place if tuberculosis elimination is to be achieved.

PULMONARY TUBERCULOSIS AMONG POLITICAL ASYLUM SEEKERS SCREENED AT HEATHROW AIRPORT, 1995-1999

Callister MEJ1, Barringer J2, Thanabalasingam ST2, Gair R2, Davidson RN1 1 Department of Infection and Tropical Medicine, Lister Unit, Northwick Park Hospital, Harrow, Middlesex HA1 3UJ 2 Health Control Unit, Terminal 3 Arrivals, Heathrow Airport, Hounslow, Middx TW6 1NB

We performed a retrospective analysis of the results of screening political asylum seekers (PAs) for pulmonary tuberculosis at Heathrow Airport between 1995 and 1999. Of the 53,911 PAs seen at Heathrow Airport HCU, 41,470 had screening CXRs performed of which 564 were considered to be suggestive of pulmonary TB. 256 of these patients were referred directly to hospital for further investigation. 100 of the 256 referred were found to have active disease, equating to an overall prevalence of 241 per 100,000, although there were large variations in disease prevalence from different geographical regions (highest from sub-Saharan Africa). We used the prevalence in each region of our screened population, extrapolated to all PAs in the UK as a whole, to estimate that 406 PAs with active pulmonary disease would have entered the country during the four year period, of whom 99 would have smear-positive disease. The frequency of drug resistance was high (22.6% of culture positive cases were isoniazid resistant, and 7.5% were multi-drug resistant TB).

ENHANCED CONTACT TRACING AND SPATIAL TRACKING OF M. TUBERCULOSIS (MTB) INFECTION BY ENUMERATION OF ANTIGEN-SPECIFIC T CELLS.

A. Lalvani1, A. Pathan1, H. Durkan2, K. Wilkinson1, A Whalen1, W. Reece1, M. Latif2, G. Pasvol2, A. Hill1. 1Nuffield Dept of Medicine, John Radcliffe Hospital, Oxford and 2Lister Unit, Northwick Park Hospital, Imperial College S.O.M, London

Identification of asymptomatic individuals with latent MTB infection is problematic because of cross-reactivity of the tuberculin skin test (TST) with BCG vaccination. The ESAT-6 antigen is specific for MTB complex but absent from BCG. Using the ex vivo enzyme-linked immunospot (ELISPOT) assay for interferon-gamma, we identified ESAT-6-specific T cells as an accurate marker of active MTB infection. To evaluate the efficacy of our assay for detecting latently infected individuals, we investigated how closely the presence of ESAT-6-specific T cells correlates with the degree of contact with an infectious index case. We studied 50 healthy contacts with varying but well-defined degrees of exposure to MTB. ESAT-6-specific T cells correlated closely with intensity of exposure (rS = 0.67), thus identifying individuals at high risk of infection; this correlation was significantly better (p = 0.03) than that observed for concurrent TST (rS = 0.32). Unlike TST, this assay successfully distinguished between MTB-exposed and BCG-vaccinated persons. This novel approach could enhance identification of latently infected individuals and thereby improve TB

TB Alert/TB Focus meeting  which was held on Wednesday, March 22, 2000

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