3 Tidligere skjermbildefunn, BCG- og tuberkulinstatus hos norskfødte tuberkulosepasienter

Previous Tuberculosis Disease or Infection in Norwegian-born Patients with Pulmonary Tuberculosis, 1975, 1985, 1995.

Einar Heldal, Helen Döcker, Aage Tverdal National Health Screening Service, Oslo, Norway.

3.1 Background

• In Norway, as in other industrialized nations, the incidence of tuberculosis has been declining rapidly since the 1940s

• Since the mid 1970s a slowing of the decline of incidence was seen, mainly due to an increasing number of cases among foreign-born residents, representing 47% of cases in 1996

• Norwegian-born cases are found predominantly among the elderly, especially men, reflecting the current low annual risk of infection

• The incidence of tuberculosis in Norway is amongst the lowest in Western Europe, but lethality in the elderly is high

• Information from Norwegian tuberculosis surveillance systems could potentially identify groups for targeted interventions for disease prevention, diagnosis and treatment

3.2 Tuberculosis surveillance in norway

• 1943 mass miniature radiography (MMR) screening started in Norway, as a means to detect active pulmonary tuberculosis, with coverage of the whole population by 1952

• 1962 the National Tuberculosis Register was established for nominal national tuberculosis case surveillance

• 1975 countrywide implementation of a selective case finding programme for MMR. A mathematical model for assigning a tuberculosis risk score to each individual determines the selection. Screening covered 30% of the population screened initially, being reduced to 3.5% by 1996

3.3 Study objectives

• Assess the proportion of Norwegian-born pulmonary tuberculosis patients with past tuberculosis disease or infection

• Assess information from Norwegian tuberculosis surveillance systems that could potentially identify groups for targeted interventions for disease prevention, diagnosis and treatment

3.4 Methods

3.4.1 Inclusion Criteria

• Registration in the National Tuberculosis Register during the years 1975, 1985 or 1995

• Norwegian-born

• With pulmonary tuberculosis confirmed by either microscopy or culture

• All cases registered in 1985 or 1995 meeting these criteria were included

• For cases registered in 1975 a 40% sample was taken

3.4.2 Data Sources

• National Tuberculosis Register- data include age at notification, sex, any previous history of tuberculosis disease, BCG vaccination status, results of tuberculin testing (Adrenalin-Pirquet)

• National Health Screening Service- results of mass miniature radiography for all chest X-rays archived for each case (tuberculosis and non-tuberculosis findings), BCG vaccination status, results of tuberculin testing (Adrenalin-Pirquet)

3.4.3 Grouping of patients

• Previous tuberculosis disease

  • Cases with previous tuberculosis disease as reported on notification forms in the National Tuberculosis Register

  • Cases with chest X-ray findings indicating previous tuberculosis disease

• Previous tuberculosis infection

  • Cases with chest X-ray findings not indicating previous tuberculosis disease, but previously natural tuberculin positive, not BCG vaccinated

  • Cases without chest X-ray information but previously natural tuberculin positive, not BCG vaccinated

• No previous tuberculosis disease or infection

  • Cases with chest X-ray findings not indicating previous tuberculosis, BCG vaccinated

  • Cases with chest X-ray findings not indicating previous tuberculosis, tuberculin negative

  • Cases without chest X-ray information, BCG vaccinated

• Unknowns

3.5 Results

3.5.1 Patients included

• In 1975, 73.0% (95/130) of an approximately 40% sample of all Norwegian-born pulmonary tuberculosis cases were smear or culture positive and were included in the study. Approximately 46.4% (231/497) of the total cases reported in 1975 would meet the study inclusion criteria.

• In 1985 35.7% (133/373) and in 1995 29.7% (70/236) of the total cases reported were pulmonary tuberculosis, Norwegian-born, with bacteriological confirmation

3.5.2 Completeness of Information

The percentage of cases with information on previous tuberculosis disease, or new cases of tuberculosis with chest X-ray information and a complete history of BCG vaccination status and tuberculin testing (adrenalin-Pirquet) was 80.0% (76/95), 76.7% (102/133) and 85.7% (60/70) for 1975, 1985 and 1995 respectively

3.5.3 The Number and Timings of Chest X-rays

• The percentage of cases identified by chest X-ray screening was 12.2% in 1975 and 6.2% in 1995

• Chest X-ray results of non -tuberculosis findings or findings indicative of tuberculosis disease remained highly consistent throughout the observation period

Most of the patients with previous TB had the disease before the introduction of effective chemotherapy

3.6 Conclusions

• Norwegian tuberculosis surveillance systems have highly complete information on past tuberculosis disease and infection for cases of pulmonary tuberculosis

• Two-thirds of Norwegian-born patients reported with pulmonary tuberculosis in the years 1975, 1985 and 1995 have had past tuberculosis disease, according to notification forms and chest X-ray findings

• An additional 10% have had past tuberculosis infection without disease

• Reactivation of past infection seems to be the main cause of pulmonary tuberculosis in Norwegian-born patients