METHODS

The setting was 119 general practices served by the Public Health Laboratory Service in Nottingham, UK. The laboratory processes all chlamydia samples for Nottingham Health District, of which approximately 40% are from primary care, 25% from GUM, 25% from other hospital settings, and 10% from family planning clinics. We were provided with an aggregated database of test numbers and diagnostic results for Chlamydia trachomatis infection (Murex EIA confirmed by BD Probetec) performed on women during 1999. Repeat tests within 4 weeks of the index test were excluded from the dataset we received, which did not contain patient identifiable information. General practice profiles for all 119 practices, including list sizes, Townsend deprivation scores, total number of principals, number of female partners per 1000 women, and number of full time equivalent practice nurses per 1000 women were obtained from Nottingham Health Authority, and linked to the laboratory database. (The Townsend score is a measure of material deprivation derived from census variables including unemployment, overcrowding, car ownership, and owner occupation—higher scores indicate increasing deprivation.)

Very few men were tested in primary care (less than one in 40 tests) and the study was therefore limited to women.

Descriptive statistics were first calculated, showing the distribution of testing. Rates of testing per 1000 women registered with general practice, the proportion of tests positive, and the number of chlamydia isolations per 1000 registered women (chlamydia isolation rate) were calculated for each of five age bands, and in relation to practice characteristics including Townsend deprivation score, list size of practice, and the number of nurses, GP principals, and female GP principals per head of population. Owing to the non-normality of the data, a non-parametric test (the Spearman rank correlation test) was then used to test for associations between key testing rates and the chlamydia isolation rate, and practice characteristics. Analysis was undertaken using stata (version 7) statistical software.

RESULTS

A total of 7172 chlamydia tests were taken in primary care. As shown in table 1, the highest proportion of positive results is seen among tests taken in women aged 15–19, followed by women aged 20–24. However, a majority of all tests (63.1%) were taken from women over the age of 25. The proportion of tests found to be positive was considerably lower for patients over the age of 30.

Table 2 summarises the association between key testing rates, chlamydia isolation rate, and practice characteristics. A higher ratio of GP principals to the registered female population was associated with higher testing rates, and with overall chlamydia isolation rate. The ratio of female GP principals to population was associated with higher testing rates only in the age group 20–24, while there was no association with the practice nurse to population ratio.

Townsend scores indicating increasing socioeconomic deprivation of the practice population were highly significantly associated with overall chlamydia isolation rate. This was not explained by higher rates of testing, nor was there an association between Townsend score and the ratio of GP principals to registered practice population.

DISCUSSION

Our findings, which confirm recent survey data,⁴ have important implications for the control of genital chlamydia infection and its cost effectiveness.

Although the percentage of positive tests was highest in younger women, the majority of tests sampled women over 25 who are at statistically lower risk of chlamydial infection.^7,8 The use of tests for C trachomatis appears to be poorly targeted in primary care. It is likely that many of these tests were used appropriately for the investigation of symptoms, such as vaginal discharge or the investigation of infertility, and this may partly explain the large number of tests in higher age groups. However, the low positive rates in women over 30 and the fact that the majority of testing takes place in women over 25 represents an opportunity cost given limited availability of testing facilities. At the time of our study, a year on year increase of approximately 35% in the number of tests in primary care was seen. The reasons for this need further exploration, as public awareness of chlamydia appears not to be related to age.⁹

The presence of female GP principals appears to be important in delivering testing to women in the 20–24 age group, as suggested by other research.¹⁰ However, it is worrying that this finding did not extend to women aged 15–19, and this suggests that their main influence may be on the threshold for screening at the time of first cervical smear test aged 20. It is possible that younger women access sexual health services elsewhere, which could explain the taking of fewer tests in this age group, but other recent data from Nottingham suggest substantial usage of primary care by young people for contraceptive services.¹¹

Men are rarely tested for chlamydia in primary care. The reasons for this finding, and its implications for disease control, need further investigation.

Our study has a number of limitations, mainly relating to the age specific data. Data were not available at the level of practitioners, and the relative roles of nurses, male doctors, and female doctors cannot be fully described. Data on age are in a single band above 30 years, which precludes inference about age specific patterns of testing above 30, and we did not have access to data on reasons for testing, which would have been helpful in understanding testing patterns in older women.

Nevertheless, our study shows that well doctored populations experienced higher rates of testing, and benefited from a higher chlamydia isolation rate. This has important implications for planned screening in primary care. Low doctor-patient ratios appear to inhibit testing, and this suggests that personnel resources may be a significant barrier to testing. The process of explaining the implications of a chlamydia test to a patient unaware of the disease takes time, and it may be that busy practices do not prioritise sexual health. The chlamydia screening pilot studies in England paid practices for tests undertaken, and recompense may be important in enabling screening in medically understaffed practices. It is important that such practice populations are not further marginalised by a screening programme which fails to take into account the problems of understaffed practices. The higher chlamydia isolation rate in practices with high Townsend score populations suggests that their participation will be important in the control of chlamydia.