Background In vivo antimicrobial resistance in C. trachomatis is still to be confirmed however there have been anecdotal reports of treatment failure. Traditionally failure has been attributed mostly to re-infection and/or non-compliance with treatment regimens. Clinical and behavioural information collected from a cohort of patients persistently infected with C. trachomatis was used to propose a case definition for treatment failure to aid patient management.

Methods Patient information was collected using a detailed clinical questionnaire. Patients were assigned to categories of most to least likelihood of treatment failure based on their self-declaration of sexual contact since initial diagnosis. Analysis and comparison within and across these categories of the clinical management and patient behaviour was performed.

Results Recruitment from a number of different settings resulted in referral of thirty-nine patients who fell into five categories based on their sexual behaviour since initial diagnosis (Table 1). Twenty declared no sexual contact (category 1), and a further thirteen declared contact that was considered low risk of re-infection (categories 2–4). The remaining six patients either did not provide enough information for accurate categorisation or had had unprotected sexual contact with a partner of unknown history (category 5) and so were excluded from further analysis.

Conclusion Using the information collected we propose a case definition of probable treatment failure for C. trachomatis as a patient with (a) at least two consecutive positive C. trachomatis specific tests e.g. NAATs, (b) full compliance with all treatment regimens prescribed in line with current national guidelines including any recommended abstinence periods and (c) no unprotected sexual contact since initial diagnosis; and confirmed failure as (a), (b), (c) and two courses of treatment with the same antimicrobial. In addition confirmation of ongoing viable infection by tissue culture methods where possible should be considered to allow antimicrobial susceptibility testing.