The present study provides evidence that verbal symptom screening for tuberculosis of migrants in primary health care centres in a low incidence country, an intervention that requires limited resources, may have a yield that is in the range of most screening programmes for migrants.
Worldwide, a variety of different strategies for migrants tuberculosis screening are in use, and effectiveness of these interventions appears to be quite variable. In a systematic review of screening programmes in Europe, which included information on pre-entry, arrival and community post arrival screening, the coverage of the programmes ranged from less than 20% to almost 100%, and it was generally lower for voluntary screening and higher when directed to asylum seekers . A variable coverage has also been observed in outreach programmes aimed at detecting active tuberculosis among disadvantaged populations in metropolitan settings. In London, the uptake of a radiographic screening conducted through a mobile unit in different settings varied from 30% to 90%, and a higher uptake was reported to be determined by the ability of local staff to engage pro-actively with clients, and providing small incentives and clear information .
In our study, among 254 individuals reporting at least one symptom suggestive of active tuberculosis, 30% were not referred for further diagnostic evaluation, mainly because the caring physician considered an alternative diagnosis more likely. Among those referred, almost half did not present to the tuberculosis clinic. The need to move to a different site for diagnostic evaluation may have contributed to the failure to complete evaluation. In a previous study conducted in Italy on active tuberculosis screening in undocumented migrants, the screening process was completed by 86% of them when chest X-ray was performed on site and in 70% of them when they were referred to another service for radiographic evaluation .
In the population studied, the probability of not attending diagnostic evaluation was lower for younger patients and tended to be higher for males and for irregular migrants. It was different in the three sites involved, although these differences were not statistically significant at the conventional 0.05 level. It has to be noted that the service with the lowest recorded rate of adherence to the screening procedures is a busy primary care clinic that provides care mainly to disadvantaged people including homeless, drug-abuser, alcoholic and extremely indigent people in addition to regular and irregular migrants. To try to increase completion of screening, the tuberculosis clinic staff tried to contact directly by phone individuals which did not show up for diagnostic evaluation and provided information of non-attendance to the participating centres, that could in turn reinforce the invitation to adhere to their clinic appointment. These data suggest that additional strategies are needed to increase the effectiveness of this intervention. These may include being interviewed by a health care worker in the same native language , active involvement of peers [18, 19], brief educational programmes [20–22] and the provision of small monetary incentives that have proven effective in favouring the acceptance of tuberculosis screening in other population groups [23, 24].
In spite of the sub optimal adherence to diagnostic procedures, the overall yield of our programme (0.33%) was in the range reported for other tuberculosis screening programmes for migrants. In a meta-analysis of screening programmes at port of entry, the overall yield of pulmonary tuberculosis was 3.5 cases per thousand screened, and this figure tended to be higher for asylum seekers and for individuals originating from Asia or Africa . Similarly, in the systematic review  of 14 national screening programmes in the European Union, a median yield of 1.8 per thousand has been recorded. Neither study provided evidence of superior effectiveness of any of the approaches to screening used.
The main difference between the programme described in the present paper and the vast majority of the tuberculosis screenings directed at new immigrants is that we did not include any laboratory or imaging tool in the first part of the screening, and these diagnostic interventions were only applied to those reporting at least one symptom suggestive of active tuberculosis. This approach is attractive because it may significantly reduce the use of resources and it may be applied when radiographic facilities are not available at the sites where target population is first screened. On the other hand, we cannot rule out that some prevalent tuberculosis cases were not identified by verbal screening. A series of studies, conducted in resource-constrained settings with high HIV prevalence, which evaluated the sensitivity of symptom based tuberculosis screening, has shown that a rule based on the presence of at least one symptom (current cough, fever, night sweats, or weight loss) had an overall sensitivity of 78.9%, and chest radiograph increased this sensitivity by 11.7% . A symptom-based approach has also been used to screen for tuberculosis among asylum seekers in Switzerland since 2006. This approach was estimated to have a 55% sensitivity compared to a 100% sensitivity of the radiographic screening carried out until 2005 . Thus, available evidence suggests that sensitivity of a symptom-based screening may be significantly lower than sensitivity of “traditional” radiographic screening.
The study design did not allow measuring to what extent verbal symptom screening may have increased the detection rate of active tuberculosis and/or reduced diagnostic delay compared to traditional passive case finding. However, a study conducted in London provides evidence that education of primary care providers to perform verbal screening for tuberculosis not only increased identification of people with latent tuberculosis but also of those with active tuberculosis . Moreover, there is evidence that active case finding based on repeated symptom screening may be effective in reducing prevalence of active tuberculosis and tuberculosis transmission in high burden settings . It can be also hypothesised that repeated screening may increase awareness of tuberculosis symptoms and the likelihood of seeking care for tuberculosis among those developing tuberculosis related symptoms.
The diagnosis of pulmonary tuberculosis has been confirmed by microbiological examinations only in three of the seven patients observed in the programme. We can speculate that this low rate of microbiological confirmation of the diagnosis could be attributed at least in part to the fact that active screening may allow the detection of tuberculosis at an earlier stage, with a lower mycobacterial burden, compared to passive case finding. This is in line with previous studies suggesting that active screening is associated with a reduction in the severity or infectivity of identified cases, with a lower proportion of cases who were symptomatic or smear or culture-positive [28–30].
On the other hand, we cannot rule out a diagnostic bias due to the inclusion in a tuberculosis screening programme.
Another limitation of the study is that we do not have information on the prevalence of HIV infection in the population studied, which may influence the clinical presentation of tuberculosis . However, in the context of active case finding there is no evidence of a different sensitivity of symptom-based screening in HIV- infected and non-infected persons [32, 33].