1. Methods

Contacts were established with health authorities in each of the 50 countries. Participation was proposed on a voluntary basis. Each country was requested to appoint one national correspondent.

A preliminary survey was conducted in September 1996 to collect information on national tuberculosis notification systems. Results of this survey were used to prepare the protocol for data collection.

Case definition

The European consensus definition of a notifiable case of tuberculosis [1] was used:

• definite case : in countries where level II laboratories (capable of identification of M. tuberculosis complex) are routinely available, a definite case of tuberculosis is a case with culture-confirmed disease due to M. tuberculosis complex. In countries where routine culturing of specimens cannot be afforded or expected, a patient with sputum smear examinations positive for acid-fast bacilli (AFB) is also considered to be a definite case.

• other than definite case : a case meeting both of the following conditions: 1) a clinician's judgement that the patient's clinical and/or radiological signs and/or symptoms are compatible with tuberculosis, and 2) a clinician's decision to treat the patient with a full course of anti-tuberculosis treatment.

All definite and other than definite incident cases notified in 1995 at national level were reportable.

Data collection

Data collected were based on the minimum set of information recommended to be reported on each case [1]:

• year of national report
• country of national report
• patient's characteristics
  • age at the start of treatment ;
    
  • gender ;
    
  • geographic origin according to place of birth.
    

• characteristics of the disease
  • new versus recurrent case (definitions left to the country) ;
    
  • site of disease, defined as pulmonary (involving the lung parenchyma and the tracheo-bronchial tree only), extra-pulmonary, or both ;
    
  • bacteriological confirmation based on positive results of the culture ;
    
  • results of smear examination for AFB (on spontaneously produced sputum).
    

Individual anonymous computerised data were requested. The choice of the software was left to the country concerned. When individual data could not be provided, countries were requested to complete six pre-defined tables including the distribution of cases by categories of the relevant variables. It was agreed that national correspondents should be responsible for the quality of the national data provided.

It was anticipated that information collected at national level in 1995 would not always fit the recommended format and definitions. To circumvent this problem, countries were offered several options :

• geographic origin
  • countries providing individual computerised data were requested to provide the country of birth, otherwise to report (by decreasing order of preference): the patient's origin based on birth place (country of report or abroad) as a binary variable, the country of citizenship, or the origin based on citizenship (binary variable).
  • countries providing aggregate data were requested to indicate which definition (birth place or citizenship) they used to classify cases by geographic origin. .

• site of disease
  • countries providing individual computerised data were requested to provide the specific major and minor site of the disease, otherwise to report the case as pulmonary versus extra-pulmonary, or as respiratory versus extra-respiratory. Respiratory tuberculosis is the category used in the International Classification of Disease (ICD9 or ICD10) and includes pulmonary tuberculosis as well as pleural and intra-thoracic lymphatic tuberculosis.
  • countries providing aggregate data were requested to indicate which definition (pulmonary or respiratory) they used to classify cases by site of disease.

• bacteriological confirmation
  • countries providing individual data were requested to provide two variables for each examination (culture and sputum smear), the first variable indicating whether the examination was performed, and the second variable indicating its results.
    
  • countries providing aggregate data were requested to classify cases as bacteriologically confirmed or not.
    

  All countries were requested to indicate whether they used the recommended case definition of a "definite" case (case with positive culture), or whether cases could be confirmed by either positive culture or positive sputum smear.
  

Material for data collection and correspondence was prepared in English and Russian. The data collection lasted from December 1996 to July 1997.

Population data

Notification rates of incident tuberculosis cases in 1995, referred to in this report as "incidence rates of notified tuberculosis", were calculated per 100 000 population, based on United Nations demographic data [2]. Rates may not fully reflect true tuberculosis incidence rates due to underreporting and other potential problems.