THAILAND’S SEROSURVEILLANCE SYSTEM BECAME SUPPLEMENTED BY A SENTINEL BEHAVIORAL SURVEILLANCE SYSTEM IN 1995
TO PROVIDE A FULLER ASSESSMENT OF CURRENT TRENDS IN THE EPIDEMIC. THE SENTINEL SITES WERE SET UP IN 20 OF THAILAND’S 76 PROVINCES. THE SENTINEL BEHAVIORAL POPULATIONS INCLUDED ARMY CONSCRIPTS, MALE AND FEMALE FACTORY WORKERS AGED 15–29 YEARS, MALE AND FEMALE
GRADE 11 STUDENTS FROM SECONDARY SCHOOLS AND PREGNANT WOMEN ATTENDING PUBLIC ANTENATAL CLINICS. THE SYSTEM
ANNUALLY COLLECTS DATA FROM 350 PERSONS PER SENTINEL POPULATION PER PROVINCE USING NON-PROBABILITY SAMPLING (QUOTA SAMPLES COLLECTED THROUGH NON-SYSTEMATIC
SELECTION OF VENUES) AND COLLECTION OF DATA THROUGH SELF-ADMINISTERED QUESTIONNAIRES [4–5]. IN PRACTICE, SOME
SENTINEL SITES DO NOT USE THE ASSIGNED SAMPLING METHODS
AND DO NOT OBTAIN SUFFICIENT SAMPLE SIZES OF SOME SUBPOPULATIONS [6]. BECAUSE OF BIASES IN THE SELECTION
PROCESS AND INADEQUATE SAMPLE SIZES, THESE SURVEILLANCE
RESULTS MAY DEVIATE SIGNIFICANTLY FROM TRUE PREVALENCE
AND CANNOT ACCURATELY DESCRIBE THE MAGNITUDE OF RISK AND TRENDS IN THIS RISK OVER TIME. THESE LIMITATIONS HAVE
BEEN PRESENT IN MULTIPLE TARGET POPULATIONS AT BOTH THE
PROVINCIAL AND NATIONAL LEVELS.