About 80% of new tuberculosis (TB) cases in Norway occur among immigrants from high incidence countries in Africa, Asia and Eastern Europe, and most of them are infected on arrival. Tuberculosis screening of immigrants from such countries is compulsory with a Mantoux test of everybody and a chest X-ray of all above 15 years of age. The aim of the screening is to identify cases of active tuberculosis in order to give treatment and stop transmission of the disease, and to offer treatment or followup for cases with latent tuberculosis.
Asylum seekers are screened at the National Reception Centre in Oslo before they are transferred to other asylum seekers centres or relocated to municipalities around the country. Internationally, there is an ongoing discussion about screening of immigrants, as well as the indications for treatment of latent tuberculosis.
The aim of the study was to assess the conduct of entry screening among asylum seekers, and the follow-up of results for active and latent tuberculosis. A secondary aim was to assess the predictive properties of QuantiFERON-TB Gold (QFT) as a potentially new screening tool for tuberculosis disease.
All asylum seekers above the age of 18 who arrived at the National Reception Centre from January 2005 to June 2006 were eligible for inclusion in the follow-up study. They were included if they had either a Mantoux test 6 mm, a positive chest X-ray, or a positive QFT test. The latter regarded the subset of asylum seekers who arrived between September 2005 and June 2006. Potential participants were excluded if they left the Reception Centre without a new address or left the country directly. Information about the study and a data collection form were sent to the health authorities in the municipalities where the asylum seekers moved to. In case anyone had moved on to another municipality in the meantime, the same information and study form were sent to the authorities in their new place of residence. If we received information that a study participant had been referred to specialist health care, a second form was sent to the health institution in question. All included study subjects were later matched with the National Tuberculosis Register which contains information about everybody diagnosed with active tuberculosis, or who have started treatment for latent tuberculosis.
An additional aim of the study of the above mentioned subsample, was to compare QFT and the Mantoux test. Everyone with a valid QFT test result where name and birth date were available were later matched with the National TB Register.
Of 4643 available asylum seekers, 2237 were included in the follow-up study. We found a valid Mantoux test result in 97.5% of them. We were on the other hand unable to ascertain and document the exact number of X-rays that were taken at the Reception Centre. Fifteen cases of tuberculosis, mainly pulmonary TB, were identified through the screening programme within two months after arrival. Altogether 28 cases of active TB had been diagnosed by the end of May 2008. Female gender, Somalian origin and a positive X-ray on arrival were all associated with active tuberculosis.
Of 314 persons with a positive X-ray, 62% had been seen by an internist in order to get a conclusive diagnosis. Similarly, of 568 asylum seekers with a Mantoux 15mm, 16% had been examined by a specialist. Only one third of persons with an elevated Mantoux test had been assessed at the community level and there was no association between the characteristics of the screening result (positive X-ray, and size of Mantoux) and the probability of being assessed. Altogether 30 cases of latent TB were started on treatment, which took place a median 17 months (range 3-36) after arrival. A Mantoux 15mm was the only characteristic that was associated with treatment induction.
The positive and negative predictive values (PPV and NPV, respectively) for Mantoux and QFT were the same. The negative predictive value for a Mantoux 6mm in combination with a negative QFT was as good as the NPV for Mantoux <15mm alone.
The conduct of the screening programme for asylum seekers was by no means in accordance with the official guidelines. Asylum seekers were screened with Mantoux on arrival, but we were unable to document the exact number who had been screened with chest X-ray. The main concern is the lack of a specialist examination of persons with a positive X-ray, but also of persons with a Mantoux 15mm. Compared to other studies, a reasonable number of cases were diagnosed with active TB within 2 months after the arrival screening. Two cases were diagnosed from 3-6 months after arrival and were probably missed by screening, but an unknown number of cases may have been lost because of insufficient follow-up of X-ray results. Six of eight cases of extra-pulmonary TB were diagnosed more than four months after arrival and could well have been ill for months before diagnosis. At the primary health care (PHC) level there was an obvious lack of a common strategy for taking responsibility for the follow-up of TB screening results.
A secondary finding was that QFT was as precise as Mantoux in predicting TB, and the negative predictive values for a Mantoux 6mm with a negative QFT were equally as precise as for a negative Mantoux alone.