ORIGINAL ARTICLE Summer heat: a cross-sectional analysis of seasonal differences in sexual behaviour and sexually transmissible diseases in Melbourne, Australia Vincent J Cornelisse, 1,2 Eric P F Chow, 1,2 Marcus Y Chen, 1,2 Catriona S Bradshaw, 1,2 Christopher K Fairley 1,2 ▸ Additional material is published online only. To view please visit the journal online (http://dx.doi.org/10.1136/ sextrans-2015-052225). 1 Central Clinical School, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Victoria, Australia 2 Melbourne Sexual Health Centre, Alfred Health, Carlton, Victoria, Australia Correspondence to Dr Vincent J Cornelisse, Melbourne Sexual Health Centre, Alfred Health, 580 Swanston St, Carlton, VIC 3052, Australia; vcornelisse@mshc.org.au; echow@mshc.org.au Received 29 June 2015 Revised 12 October 2015 Accepted 17 October 2015 Published Online First 6 November 2015 To cite: Cornelisse VJ, Chow EPF, Chen MY, et al. Sex Transm Infect 2016;92:286–291. ABSTRACT Objectives To date, no study has correlated seasonal differences in sexual behaviour with the seasonal differences in sexually transmitted infections (STIs); and no seasonal study of STIs has been conducted in the southern hemisphere. Our study aimed to describe seasonal differences in sexual behaviour and correlate this with seasonal differences in STI diagnoses in Melbourne, Australia. Method This was a cross-sectional study of individuals attending the Melbourne Sexual Health Centre over a 9- year period from 2006 to 2014. We conducted separate analyses for men who have sex with men (MSM) and men who have sex with women (MSW), and women. Seasonal patterns of sexual behaviour and STI positivity were examined within each group. Results All groups reported a higher number of partners over the preceding three months for consultations in summer compared with winter (MSM mean 5.48 vs 5.03; MSW mean 2.46 vs 2.31; women mean 1.83 vs 1.72). Urethral gonorrhoea diagnoses among MSM were higher in summer compared with winter (OR 1.23, 95% CI 1.04 to 1.46). Similarly, non- gonococcal urethritis (NGU) diagnoses among MSW were the highest in summer (OR 1.11, 95% CI 1.03 to 1.20), but there was no seasonal difference in NGU diagnoses when we adjusted for partner numbers. In women, pelvic inflammatory disease (PID) diagnoses peaked in autumn, when rates were higher than in winter (OR 1.30, 95% CI 1.09 to 1.55). Conclusions Our results describe a peak in sexual partner number and STI diagnoses during consultations in summer in men and a rise in PID in autumn in women. INTRODUCTION If there is a seasonal difference in rates of sexually transmitted infections (STIs), then public health campaigns could be most effective if they were timed accordingly. Previous studies in the USA have shown a peak in rates of STIs in summer and early autumn. 1–3 Two studies in the UK 45 have shown a two-peak seasonal distribution in STI incidence, with peaks in both the first quarter and third quarter of the year, corresponding to the time after Christmas holidays and summer holidays, respect- ively. A study of gonorrhoea and urethritis rates in Saharan Africa 6 also reported a seasonal difference, with highest rates from January to May, coinciding with the postharvest season during which young adults migrate for work, and perhaps is a parallel for the ‘summer break’ period in the USA. None of these studies correlated the seasonal difference in STI rates with seasonal differences in behavioural risk factors for STI such as partner numbers and condom use. Other studies have assessed seasonal differences in sexual behaviours without assessing STI rates. A study conducted in the USA observed a peak of first sexual intercourse or ‘loss of virginity’ in June through to August; this seasonal difference was more pronounced in school-aged teenagers than in older youths, suggesting that school holidays may be an influence. 7 A small prospective cohort study of sexual behaviour amongst women in the USA 8 recorded increased sexual activity in summer, but no increase in number of partners. Condoms were used more consistently in summer than in winter. A study in the UK 5 reported an increase in preg- nancy terminations in the first quarter of the year, corresponding to what are presumed to be unin- tended conceptions around the Christmas period. Correspondingly, they showed peaks in condoms sales over Christmas and over summer. To date, no study has compared seasonal differ- ences in sexual behaviour and other STI risks with seasonal differences in STI positivity; and no sea- sonal study has been conducted in the southern hemisphere. The aim of this study was to assess and correlate these seasonal differences in order to inform the design and timing of public health cam- paigns targeted to reduce STI rates in Australia. METHODS This was a cross-sectional study of all individuals attending the Melbourne Sexual Health Centre (MSHC) over a 9-year period from 1 January 2006 to 31 December 2014 inclusive. As of 2013, the MSHC provided approximately 35 000 sexual health consultations annually, about 37% of these for men who have sex with men (MSM). 9 It is a free walk-in service; no referrals are required. Prior to seeing the triage nurse, attendees complete a computer-assisted self-interview (CASI) that collects their demographic details and history of sexual behaviours and drug use. 10 On most days, a small number of patients are triaged out of the service due to the service operating at full capacity. The triage nurse makes the triaging decision after patients have completed their CASI questionnaire. Editor’s choice Scan to access more free content 286 Cornelisse VJ, et al. Sex Transm Infect 2016;92:286–291. doi:10.1136/sextrans-2015-052225 Epidemiology on June 12, 2020 by guest. Protected by copyright. http://sti.bmj.com/ Sex Transm Infect: first published as 10.1136/sextrans-2015-052225 on 6 November 2015. Downloaded from