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1.  Population attributable risk for chlamydia infection in a cohort of young international travellers (backpackers) and residents in Australia 
BMJ Open  2011;1(1):e000004.
Aim
To estimate the population attributable risk (PAR) for Chlamydia trachomatis infection in young men and women in Sydney, Australia.
Method
Multivariate logistic regression was used to examine the association between demographic, sexual behaviour and other potential risk factors and chlamydia positivity in young (≤30 years) heterosexual international travellers (backpackers) and Australian residents attending a sexual health clinic. Point and interval estimates of PAR were calculated to quantify the proportion of chlamydia infections that can theoretically be prevented if a combination of risk factors is eliminated from a target population.
Results
In males, the PAR associated with inconsistent condom use in the past 3 months was 65% (95% CI 56% to 71%) in backpackers compared to 50% (95% CI 41% to 56%) in non-backpackers and the PAR associated with reporting three or more female sexual partners in the past 3 months was similar between male backpackers and non-backpackers (33% (95% CI 28% to 40%) and 36% (95% CI 32% to 41%), respectively). In females, the PAR associated with inconsistent condom use in the past 3 months was 51% (95% CI 42% to 59%) in backpackers compared to 41% (95% CI 31% to 51%) in non-backpackers, and the PAR associated with reporting three or more male sexual partners in the past 3 months was 14% (95% CI 11% to 18%) in backpackers compared to 30% (95% CI 25% to 37%) in non-backpackers.
Conclusion
These findings suggest that the largest number of chlamydia infections could be avoided by increasing condom use, particularly in backpackers. Reporting multiple partners was also associated with a large proportion of infections and the risk associated with this behaviour should be considered in health promotion strategies.
Article summary
Article focus
Risk factors for chlamydia infection were determined among young, heterosexual backpackers and Australian residents.
A novel statistical methodology was used to investigate the potential impact of eliminating risk factors on chlamydia infection at a population level.
Key messages
Results suggest that the majority of the chlamydia infections could be avoided by increased condom use, particularly among backpackers.
Multiple sex partners in past 3 months was also associated with a high proportion of chlamydia infections at the population level.
Strengths and limitations of this study
This is the first study to investigate the potential impact of sexual risk behaviours for chlamydia infection at the population level.
The study population was sexual health clinic attendees who are likely to be at higher risk for chlamydia infection compared to the general population.
doi:10.1136/bmjopen-2010-000004
PMCID: PMC3191383  PMID: 22021720
Hepatitis C; HIV; HIV testing; homosexuality; infectious disease
2.  Developing and validating a risk scoring tool for chlamydia infection among sexual health clinic attendees in Australia: a simple algorithm to identify those at high risk of chlamydia infection 
BMJ Open  2011;1(1):e000005.
Objective
To develop and validate a risk scoring tool to identify those who are at increased risk of chlamydia infection.
Methods
We used demographic data, sexual behaviour information and chlamydia positivity results from more than 45 000 individuals who attended Sydney Sexual Health Centre between 1998 and 2009. Participants were randomly allocated to either the development or internal validation data set. Using logistic regression, we created a prediction model and weighted scoring system using the development data set and calculated the odds ratio of chlamydia positivity for participants in successively higher quintiles of score. The internal validation data set was used to evaluate the performance characteristics of the model for five quintiles of risk scores including population attributable risk, sensitivity and specificity.
Results
In the prediction model, inconsistent condom use, increased number of sexual partners in last 3 months, genital or anal symptoms and presenting to the clinic for sexually transmitted infections screening or being a contact of a sexually transmitted infection case were consistently associated with increased risk of chlamydia positivity in all groups. High scores (upper quintiles) were significantly associated with increased risk of chlamydia infection. A cut-point score of 20 or higher distinguished a increased risk group with a sensitivity of 95%, 67% and 79% among heterosexual men, women and men who have sex with men (MSM), respectively.
Conclusion
The scoring tool may be included as part of a health promotion and/or clinic website to prompt those who are at increased risk of chlamydia infection, which may potentially lead to increased uptake and frequency of testing.
Article summary
Article focus
The authors created a risk assessment tool that allows people to estimate their own chlamydia risk score based on simple non-invasive variables.
Key messages
The tool described here will potentially provide a simple and cost-effective method of identifying and alerting individuals who would benefit from chlamydia screening.
This tool may be included as part of a health promotion and/or clinic website.
This tool may potentially lead to increased uptake and frequency of testing.
Strengths and Limitations
This is the first study to utilize statistical methods to derive a locally-specific assessment tool using 12 years of data from more than 45 000 men and women.
The Study population was sexual health clinic attendees who are likely to be at higher risk for Chlamydia infection compared to the general population.
doi:10.1136/bmjopen-2010-000005
PMCID: PMC3191384  PMID: 22021721
Chlamydia infection; risk prediction; hepatitis C; HIV; HIV testing; homosexuality; infectious disease; epidemiology; sexual medicine; health informatics

Results 1-2 (2)