Aims Prisoners include a disproportionate number of those with social and clinical risk factors for tuberculosis and pose a challenge for control. The aim of this study was to investigate the characteristics of prisoners with tuberculosis in order to inform clinical management and control policy.
Methods Between 2004 and 2007, 205 patients newly diagnosed as having tuberculosis in prison in the UK identified in national surveillance reports were studied. Isolates from prisoners were tested for susceptibility to first-line antituberculosis drugs and strain typed where possible.
Results Prisoners were significantly more likely to be UK-born (47 vs 25%), to be white (33 vs 22%) and to have pulmonary disease (75 vs 56%) than other tuberculosis patients. Pulmonary cases were also more likely to be sputum-smear-positive (69 vs 57%). Over one-third of culture confirmed cases among prisoners were resistant to isoniazid. Less than half (48%) of patients diagnosed as having tuberculosis in prison completed treatment, with a fifth lost to follow-up.
Discussion In the UK, imprisonment is an important risk factor for tuberculosis, especially drug-resistant and infectious forms of the disease. The management of tuberculosis among UK prisoners is further complicated by high rates of loss to follow-up care and poor treatment outcomes.
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Tuberculosis continues to be a major public health problem in the UK. Although overall incidence is low at 14 per 100 000, increased risk of disease is concentrated in major cities, among people born abroad and other groups with specific risk factors.1 Prisoners are recognised to be at higher risk of tuberculosis in the UK,2 USA,3 and several eastern4 5 and western European states.6–8
Prisoners include a disproportionate number of those with social and clinical risk factors for infection and progression to active disease, such as drug and alcohol abuse,6 7 homelessness9 and HIV infection.7 10 Tuberculosis transmission incidents have also been reported in UK prisons,11 and a large outbreak of drug-resistant tuberculosis in London has been linked to imprisonment in many of the cases.12
This study investigated the characteristics of prisoners compared with other individuals newly diagnosed as having tuberculosis in England and Wales between 2004 and 2007, including treatment outcome and assessing for evidence of clustering.
Prisoners were identified among cases reported to national tuberculosis surveillance between 2004 and 2007 in England and Wales. This included clinical case reports (Enhanced Tuberculosis Surveillance, ETS) and mycobacterial laboratory reports (the UK Mycobacterial Surveillance Network, MycobNet). Information on imprisonment is not routinely recorded in these reports but was determined from searching occupation and address fields. A pilot surveillance scheme of prisoners with tuberculosis in London was also used. Cases were defined as being in prison at the time of tuberculosis diagnosis. Children aged less than 16 years and detainees in Immigration Removal Centres (those awaiting deportation after failed asylum applications) were excluded.
Demographic and clinical characteristics of prisoners reported to national ETS during this period were compared with all other notified cases aged 16 years or more. Proportions were compared using the χ2 test or Fisher exact test in Stata 9.2.
Isolates identified as from prisoners, and archived at the HPA National Mycobacterium Reference Unit in London, were genotyped using 15 loci mycobacterial interspersed repetitive unit/variable number tandem repeat (MIRU/VNTR) analysis.13 The proportion of clustered isolates was calculated using the n-1 method.14
Over 4 years, 205 prisoners with tuberculosis were identified. Of these, 179 were reported to national ETS, making up less than 1% of all tuberculosis cases (29 340 cases aged 16 or older) reported during this period (figure 1).
Compared with other patients, prisoners were more often born in the UK (47% vs 25%) and of black Caribbean (18% vs 2%) or white ethnicity (33% vs 22%) (table 1). They were also more likely to have pulmonary (75% vs 56%) and sputum-smear-positive disease (69% vs 57% of pulmonary cases).
A very high proportion of prisoners had drug-resistant tuberculosis, with over a third (35%) resistant to isoniazid. This means that a minimum of 4% (48/1190) of all isoniazid resistant tuberculosis cases reported in this time occurred in prisoners, rising to more than one in 10 (11%, 25/228) among UK-born individuals. Most were part of the ongoing outbreak in London.12
Prisoners also had poorer treatment outcomes than other patients: less than half completed treatment within a year (48% vs 80%, table 2). Although 13% were still on treatment, 21% were lost to follow-up. More than half of those lost had isoniazid resistant disease (55%, 12/22) at the start of their treatment. Although fewer died before completing treatment, prisoners' median age at death was lower than other patients (48 vs 70 years).
MIRU/VNTR typing results were available on 57 cases (40% of 143 culture confirmed cases), 60% of which (34 cases, ‘n-1’ method) were clustered (Appendix 1). Almost all (32, 56%) were in one cluster, containing predominantly the north London isoniazid-resistant outbreak isolates.12 Due to the predominance of the outbreak strain, clustered cases reflect characteristics associated with this.12 Clustered cases were more often UK-born and black Caribbean, and were also less likely to be lost to follow-up, and more often still on treatment after 1 year (see online Appendix 2).
This study found extremely high levels of drug resistance among tuberculosis cases diagnosed while in prison in the UK. Prisoners were also more likely to have infectious forms of disease and not complete treatment, with management complicated by transfer, release and social factors.
The number of prisoners identified with tuberculosis in this study is likely to be a minimum estimate. Only cases in prison at the time of diagnosis were included, so those with a history of imprisonment were excluded. The study also could not include undiagnosed or unreported cases among prisoners, and those reported but unidentifiable as prisoners. As imprisonment was not routinely collected through national surveillance, this relied on searching occupation and address fields. By using multiple data sources, a number of cases were identified that had not been reported to national surveillance: in particular, 12 culture confirmed cases had not been reported.
Tuberculosis incidence cannot be reliably estimated among prisoners in England and Wales from these data. As stated, our numerator is likely to be a minimum estimate. Determining an accurate denominator for the prison population in the study period was also problematic due to the high turnover of prisoners, many having received short remand sentences, and difficulties in obtaining duration of imprisonment required to calculate person time at risk. Previous estimates of incidence in similar settings have ranged from 215 per 100 000 prisoners in Paris6 to 2775 per 100 000 prisoners in Barcelona.7 High prevalence of tuberculosis among prisoners assessed through cross-sectional surveys has also been reported from London (208 per 100 000)2 and Italy (290 per 100 000).8
The high levels of drug resistance and low proportion of prisoners completing treatment within 1 year is concerning. Although more drug resistance leads to a greater number still on treatment at 1 year, many prisoners were lost to follow-up, a potentially avoidable outcome that further increases the risk of onward transmission and drug resistance. This supports previous findings of high rates of drug-resistant disease and poor treatment adherence among prisoners in London.2
The fact that cases who were part of the isonaizid-resistant outbreak were less likely to be lost to follow-up than other prisoners probably reflects increased use of directly observed therapy (DOT) on the advice of an Outbreak Control Committee.12 DOT has been found to improve treatment completion compared with self administration among tuberculosis patients released from prison, particularly if administered at a field site.15 High levels of treatment adherence among prisoners is achievable, even after release, with adequate coordination between programmes both within and external to the prison (such as methadone maintenance programmes, and housing or other social support) as demonstrated in previous studies.16
The large proportion of clustered cases should be interpreted with caution, as this only represents 40% of culture confirmed cases. As routine prospective typing was not done for all cases, those suspected as being part of an outbreak (due to isoniazid resistance or other factors) were more likely to be typed. Nevertheless, the identification of patients with indistinguishable strain types reflects appreciable levels of transmission.
Attributing transmission to imprisonment, however, is not possible in this study. Over-representation of high-risk groups among prisoners is a known factor in explaining higher incidence, but the congregate settings of prisons may contribute to transmission. Delay between infection and onset and the high turnover of prison populations also mean difficulties identifying the source and site of infection. An Australian study found that increased incidence among prisoners was not attributable to prison environment:17 in Spain, however, recent transmission was associated with lengthy incarceration, overcrowding and delayed diagnosis within prisons.7
High rates of tuberculosis, especially drug-resistant tuberculosis, among prisoners along with low levels of successful treatment mean prisoners present a particular challenge for tuberculosis control. These findings support national guidance recommending prisoners to be screened on entry, all those on treatment to receive DOT, and continuity of care ensured for transferred and released cases.18 The importance of this is highlighted by the situation in Russia, where failure to treat prisoners successfully is a significant driver of the tuberculosis epidemic and high rates of drug resistance.5
Initiatives are under way to strengthen tuberculosis control in UK prisons. National tuberculosis surveillance now includes current and previous imprisonment, and other social risk factors. This, combined with universal prospective strain typing, will allow a more comprehensive assessment of the contribution of imprisonment to tuberculosis in the UK, and aid evaluation of interventions. A digital teleradiology network is being installed across London prisons and key regional prisons to screen new prisoners and transfers on arrival. Screening prisoners for tuberculosis with chest radiography has been shown to be a cost-effective intervention to strengthen tuberculosis control among high-risk populations that may be reached through screening in prisons.19 Improving treatment outcomes among these complex cases through increased use of DOT, social and housing support is an essential step to control tuberculosis successfully in the UK.
What is already known on this topic
Prisoners are known to be at increased risk of tuberculosis infection and disease. Failure to successfully treat prisoners is a significant driver of the tuberculosis epidemic and high rates of drug resistance in other countries. This is the first national study investigating the characteristics of prisoners with tuberculosis in the UK.
What this study adds
This study shows very low proportions of tuberculosis cases diagnosed in UK prisons successfully completing treatment, with one in five lost to follow-up. The study also demonstrates very high levels of drug resistance among prisoners with tuberculosis. Improving treatment outcomes among these complex cases is essential to successfully control tuberculosis in the UK.
Cluster analysis of 57 isolates from patients identified as prison inmates
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.
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