title: Summer heat: a cross-sectional analysis of seasonal differences in sexual behaviour and sexually transmissible diseases in Melbourne, Australia.
abstract: 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.
  
  
  
  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.
  
  
  
  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).
  
  
  
  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.
authors.affiliation: Central Clinical School, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Victoria, Australia Melbourne Sexual Health Centre, Alfred Health, Carlton, Victoria, Australia.
authors.forename: Vincent J
authors.identifier: 0000-0003-0657-9677
authors.initials: VJ
authors.lastname: Cornelisse
authors.affiliation: Central Clinical School, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Victoria, Australia Melbourne Sexual Health Centre, Alfred Health, Carlton, Victoria, Australia.
authors.forename: Eric P F
authors.initials: EP
authors.lastname: Chow
authors.affiliation: Central Clinical School, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Victoria, Australia Melbourne Sexual Health Centre, Alfred Health, Carlton, Victoria, Australia.
authors.forename: Marcus Y
authors.initials: MY
authors.lastname: Chen
authors.affiliation: Central Clinical School, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Victoria, Australia Melbourne Sexual Health Centre, Alfred Health, Carlton, Victoria, Australia.
authors.forename: Catriona S
authors.initials: CS
authors.lastname: Bradshaw
authors.affiliation: Central Clinical School, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Victoria, Australia Melbourne Sexual Health Centre, Alfred Health, Carlton, Victoria, Australia.
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Fairley
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001315:Australia / Q000453:epidemiology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D000292:Pelvic Inflammatory Disease / Q000453:epidemiology*; D012621:Seasons; D012725:Sexual Behavior / Q000523:psychology / Q000706:statistics & numerical data*; D012747:Sexual Partners / Q000523:psychology*; D012749:Sexually Transmitted Diseases / Q000453:epidemiology*
keywords: EPIDEMIOLOGY (CLINICAL); GONORRHOEA; PELVIC INFLAMMATORY DISEASE; SEXUAL BEHAVIOUR; URETHRITIS