Under-reporting of sexually transmitted infection with chlamydia trachomatis - a revision of surveillance system is required

INTRODUCTION: To consider whether a revision of the national chlamydia surveillance system is needed, the objectives were to estimate the proportion of laboratory confirmed cases at the Institute of Microbiology and Immunology (IMI) not reported to the National Institute of Public Health (NIPH), and to assess the completeness of reporting for individual data items. METHODS: The dataset with information about the cases diagnosed at the IMI during 2007-2010, and the national chlamydia surveillance data at the NIPH, were linked using SOUNDEX code and the date of birth as unique identifier. The proportion of unreported cases was calculated. The proportions of records with missing data for individual variables were estimated for all reported cases during the same period. Chlamydia testing and reported rates for the period 2002-2010 were presented. RESULTS: Of 576 laboratory confirmed chlamydia cases at the IMI during 2007-2010, 201 were reported to the NIPH, corresponding to 65.1% of the overall underreporting (50.4% among dermatovenerologists, 90.1% among gynaecologist and 100% among other specialists). Item response was above 99% for demographic variables and from 69% to 81% for sexual behaviour variables. Higher testing rates corresponded to higher diagnosed rates. CONCLUSIONS: Surveillance data underestimated diagnosed chlamydia infection rates. Mandatory reporting of cases by laboratories with less variables, including unique identifier, gender, date of diagnosis, and reporting physician specialty, together with numbers of tests performed (for estimating testing and positivity rates) would simplify the surveillance system and eliminate underreporting of laboratory confirmed cases, while still providing necessary information for public health policies.