Analysis of chlamydia contacts and the look-back interval at a UK sexual health clinic.

Guidance on contact tracing in (CT) is limited. CT contacts data over 12 months (1 December 2018-29 November 2019) at a UK sexual health clinic were analysed to determine the appropriateness of the currently recommended six-month 'look-back' interval. Age and sex of CT contacts were associated with clinical outcomes. Subgroups of 100 CT positive/negative contacts (each = 100) were randomly selected. The relationship between time since sexual intercourse with the index case (Last Sexual Intercourse; LSI) and CT positivity was examined; suitability of varying look-back intervals was explored. Of 891 CT contacts (mean age = 25.0 years, 66.2% men), 66.9% tested positive for CT. Positive CT contacts were significantly younger (23.8 ± 6.8 years vs. 27.4 ± 9.1, < 0.001) and more often women (36.4% vs. 28.5%, = 0.018) than negative contacts. In the subgroups, the Mann-Whitney U test revealed no significant difference between the LSI of positive and negative contacts ( = 0.081). 95% of positive CT contacts ( = 82) were captured within a hypothetical three-month look-back interval. While most CT positive contacts were captured within three months, they appeared to remain proportionately represented beyond this point. Although this supports current guidelines, further research should investigate whether CT contacts involved in longer look-back intervals may require disproportionately greater resources to trace.