Estimating tuberculosis case detection rate in resource-limited countries: a capture-recapture study in Egypt

SETTING

Most countries endemic and highly endemic for tuberculosis (TB) still do not have reliable TB surveillance systems. Indirect estimation of TB incidence is needed to monitor the performance of the National Tuberculosis Programme (NTP) in the context of the World Health Organization implementation and impact targets for TB control.

OBJECTIVE

To estimate the case detection rate (CDR) of all TB cases and sputum smear-positive TB cases in Egypt in 2007.

METHODS

Record linkage and three-source capture-recapture analysis of data collected through active prospective longitudinal surveillance within the public and private non-NTP sector in four Egyptian governorates selected by stratified cluster random sampling.

RESULTS

For all TB cases, the estimated CDR of NTP surveillance and completeness of case ascertainment after record linkage was respectively 55% (95%CI 46-68) and 62% (95%CI 52-77). For sputum smear-positive TB cases, these proportions were respectively 66% (95%CI 55-75) and 72% (95%CI 60-82).

CONCLUSION

This pilot study shows that representative sampling, prospective surveillance in the non-NTP sector, record linkage and capture-recapture analysis can improve CDR estimation. For global, standardised and reliable use, this methodology should be further developed. Until then, all resource-limited countries should strengthen their national surveillance systems in the context of the Stop TB strategy.

Risk factors for recurrent tuberculosis in England and Wales, 1998-2005

BACKGROUND

Information on recurrent tuberculosis can provide an indication of the effectiveness of tuberculosis services and identify patients who are most vulnerable. The objective of this study was to estimate the incidence of, and investigate risk factors for, recurrent episodes of tuberculosis in England and Wales.

METHODS

Episodes of recurrent tuberculosis were identified among prospectively collected records of tuberculosis cases reported to the Health Protection Agency between 1998 and 2005. An episode of recurrent tuberculosis was defined as a re-notified case in the same patient after at least 12 months from the date of the initial notification. To estimate incidence, follow-up time was calculated for all cases until re-notification or censure. Multivariable Cox proportionate hazard models were used to determine hazard ratios (HR) for recurrence of tuberculosis and investigate the risk associated with clinical, demographic and microbiological factors.

RESULTS

Five hundred and eighty-eight recurrent tuberculosis events were identified among 53 214 cases reported between 1998 and 2005, a rate of 4.1 (95% CI 3.8 to 4.5) episodes per 1000 person years of follow-up. Factors independently associated with a greater risk of recurrent tuberculosis were HIV co-infection (HR 1.64, 95% CI 1.13 to 2.38) and belonging to a South Asian ethnic group (HR 1.54, 95% CI 1.23 to 1.93).

CONCLUSION

Tuberculosis recurrence is uncommon in England and Wales despite the absence of a universal directly observed treatment policy. The identification of HIV co-infection as a risk factor for recurrent tuberculosis is consistent with findings elsewhere. The higher risk among South Asians, however, requires further investigation.

Investigating tuberculosis trends in England

OBJECTIVE

To investigate the factors associated with the increasing incidence of tuberculosis in England.

DESIGN

Prospective national surveillance study.

METHODS

Measurement of relative trends in demographic, clinical and microbiological characteristics of tuberculosis cases reported in England between 1999 and 2003.

RESULTS

Between 1999 and 2003, the number of tuberculosis cases reported in England increased by 19% from 5539 to 6608. Significant increases in tuberculosis cases were seen in the non-UK-born population who were recent entrants to the UK (arrival less than 5 years prior to diagnosis) relative to cases in the UK-born population, both in London [1.08; 95% confidence interval (CI) 1.02-1.14] and outside London (1.22; 95% CI 1.16-1.28). Cases of tuberculosis co-infected with human immunodeficiency virus (HIV) increased significantly both in London (1.19; 95% CI 1.12-1.27) and outside London (1.22; 95% CI 1.12-1.33) relative to cases not known to be co-infected with HIV. Small increases in the number of cases living in less-deprived areas were observed relative to those in the most-deprived areas (1.11; 95% CI 1.02-1.21) in London. The number of cases of isoniazid-resistant (1.09; 95% CI 1.02-1.16) and multi-drug-resistant tuberculosis (1.22; 95% CI 1.02-1.45) increased relative to drug-susceptible cases in London.

CONCLUSIONS

Tuberculosis remains strongly associated with deprivation, but no real change in the distribution of tuberculosis cases by deprivation was observed over the study period. The proportion of tuberculosis cases co-infected with HIV has increased, but migration explains most of the recent trends in tuberculosis in England. Measures that target latent tuberculosis infection could have an increased role to play alongside measures against active disease in reducing the incidence of tuberculosis in the UK.

Estimating tuberculosis case mortality in England and Wales, 2001-2002

SETTING

England and Wales, 2001-2002.

OBJECTIVE

To obtain a more accurate estimate of tuberculosis (TB) case fatality within 12 months of starting treatment or notification among TB cases reported to the national surveillance system.

METHODS

Records of deaths for all TB cases reported to the national surveillance system were identified using linkage to two other sources of mortality information: the National Health Service (NHS) central register and death registrations from the Office for National Statistics (ONS). These data were compared to reports of deaths ascertained by national TB surveillance through treatment outcome monitoring. Capture-recapture methodology was used to estimate any remaining unascertained deaths for the final calculation of the case fatality rate (CFR).

RESULTS

In total, 1169 deaths (95%CI 1140-1224) were identified among 13176 cases (CFR 8.9%, 95%CI 8.7-9.3%). Data linkage with the NHS central register and death registrations from the ONS identified a further 255 deaths not recorded by national TB surveillance. Capture-recapture estimated 61 (95%CI 32-116) unascertained deaths.

CONCLUSION

Mortality among TB cases is underestimated by national TB surveillance. Real-time data linkage between case reports and death registrations would allow a more accurate and timely estimate of TB mortality.

Investigating urban-rural disparities in tuberculosis treatment outcome in England and Wales

The purpose of this study was to compare the occurrence of tuberculosis (TB) and the outcome of treatment between TB patients living in urban and rural areas. Cases of TB reported from 2001 to 2003 in England and Wales were assigned to a rural or urban area classification. The outcome of interest, non-completion of treatment, was investigated to determine the odds ratio for urban vs. rural residence. The effects of age, sex, ethnicity, place of birth, time since arrival in the United Kingdom, disease site, isoniazid resistance and previous diagnosis were adjusted for by multivariable logistic regression. Crude odds ratios showed a significantly higher level of treatment non-completion in rural areas. These results became non-significant (OR 1.02, 95% CI 0.83-1.26, P=0.82) after adjusting for the confounding effects of ethnic group and age. In England and Wales residence in a rural location is not an independent determinant of TB treatment outcome failure.