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Epidemiology poster session 4: Methodological aspects
P1-S4.02 Ethnicity based on the country of birth is better to identify the young population at high risk for Chlamydia infection than self-defined ethnicity
  1. A Haasnoot1,
  2. F D H Koedijk1,
  3. E L M Op de Coul1,
  4. M A B van der Sande1,
  5. H M Götz2,
  6. J F A Fennema3,
  7. I V F van den Broek,
  8. on behalf of the CSI group1
  1. 1National Institute for Public Health and the Environment, RIVM, Bilthoven, Netherlands
  2. 2Rotterdam-Rijnmond Public Health Service, Rotterdam, Netherlands
  3. 3Amsterdam Public Health Service, Amsterdam, Netherlands

Abstract

Background Chlamydia infections are frequently found in young persons and ethnic minorities. Ethnicity can be defined in different ways. In this study, ethnic disparities in Chlamydia trachomatis positivity in the Netherlands were assessed comparing two definitions of ethnicity. The study objective was to determine which definition is most useful to discriminate persons at risk for Chlamydia infection.

Methods Chlamydia positivity rates in persons aged 16−29 years, were investigated using data from the first round of the Chlamydia Screening Implementation (CSI, 2008−2009) and surveillance data from specialised at STI centres in the Netherlands (2009), comparing self-defined ethnicity and ethnicity based on the country of birth of a person and his parents (first and second generation immigrants). The relation between ethnicity and Chlamydia positivity rates were evaluated using logistic regression, adjusting for age, sex and SES, in both data sets.

Results Overall, the Chlamydia positivity rate was 13 % in the STI centres, and 5% in CSI. Being a young (first or second generation) immigrant was associated with Chlamydia positivity in both CSI (adjusted OR 2.3 [95% CI 2.0 to 2.6]) and the STI centres (adjusted OR 1.4 [95% CI 1.3 to 1.5]). Classifying the population by self-defined ethnicity resulted in a considerable group labelling themselves as Dutch (57% of the immigrants in CSI and 60% of those in the STI centres), especially second generation immigrants (72% in CSI and 80% in the STI centres). Self-defined non-Dutch ethnicity showed similar associations with testing positive in CSI (OR 2.4 [95% CI 2.1 to 2.7]) and the STI centres (OR 1.2 [95% CI 1.0 to 1.3]), but the model basing ethnicity on country of birth of a person and his parents had a better fit (higher likelihood). Self-defined ethnicity may allow for more personal input, this however also makes it a dynamic variable: in the second round of CSI, 15% of the immigrants identified themselves by a different ethnicity than in the first round see Abstract P1-S4.02 Figure 1.

Abstract P1-S4.02 Figure 1

Chlamydia positivity rate by region of origin, by self-defined ethnicity, in young persons in the Chlamydia Screening Implementation (CSI) and the Dutch STI centres.

Conclusions Both self-defined ethnicity and ethnicity based on the country of birth of a person and his parents, can be used to detect young persons at a higher risk of Chlamydia infection. However the definition of ethnicity based on the country of birth explains variation in the Chlamydia data better and is objective and constant, whereas self-defined ethnicity would disregard a large part of the young population at higher risk for Chlamydia infection.

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