title: Climatic influence on the prevalence of noncutaneous disease flare in systemic lupus erythematosus in Hong Kong.
abstract: OBJECTIVE
  It is generally agreed that there is a seasonal variation in the prevalence of cutaneous manifestations of systemic lupus erythematosus (SLE). We investigated whether there is seasonal variation in the incidence of noncutaneous lupus flare in Hong Kong.
  
  
  METHODS
  We reviewed all noncutaneous lupus flare in 222 consecutive patients with SLE followed in our clinic from 1995 to 2005. Specific organ involvement of each flare was reviewed. The variation in the prevalence of lupus flare by calendar month and the relation with climatic factors were determined.
  
  
  RESULTS
  The total followup was 18,412 patient-months. In total, there were 313 episodes of noncutaneous flare recorded in 129 patients. There were more lupus flares in December and January [2.31 episodes, vs 1.58 episodes per 100 patient-months for other calendar months; relative risk (RR) 1.46, 95% CI 1.12-1.90, p = 0.004], and more flares of lupus nephritis in December and January (1.14 episodes, vs 0.60 episodes per 100 patient-months for other calendar months; RR 1.90, 95% CI 1.29-2.80, p = 0.001). There were more cases of membranous nephropathy in December and January (0.46 episode, vs 0.18 episode per 100 patient-months for other calendar months; RR 2.59, 95% CI 1.36-4.93, p = 0.0027), while the variation in prevalence of proliferative lupus nephritis was not statistically significant. There was also a significant U-shape correlation between the rate of lupus flare and the monthly average environmental temperature (r = 0.802, p = 0.0096), with higher flare rate at extremes of temperature.
  
  
  CONCLUSIONS
  We found substantial seasonal variation in the incidence of noncutaneous flare in our SLE patients, with peak incidence in December and January. There was a U-shaped relation between environmental temperature and the prevalence of noncutaneous flare. Keeping a warm living environment and avoiding exposure to extremes of temperature may help to reduce flare for SLE patients in subtropical countries.
authors.affiliation: Department of Medicine and Therapeutics, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, China. ccszeto@cuhk.edu.hk
authors.forename: Cheuk-Chun
authors.initials: CC
authors.lastname: Szeto
authors.forename: Hing-Yim
authors.initials: HY
authors.lastname: Mok
authors.forename: Kai-Ming
authors.initials: KM
authors.lastname: Chow
authors.forename: Tsz-Cheung
authors.initials: TC
authors.lastname: Lee
authors.forename: John Yin-Kong
authors.initials: JY
authors.lastname: Leung
authors.forename: Edmund Kwok-Ming
authors.initials: EK
authors.lastname: Li
authors.forename: Thomas Kai-Cheung
authors.initials: TK
authors.lastname: Tsui
authors.forename: Samuel
authors.initials: S
authors.lastname: Yu
authors.forename: Lai-Shan
authors.initials: LS
authors.lastname: Tam
mesh_terms: D000328:Adult; D002980:Climate; D005260:Female; D006723:Hong Kong; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000150:complications*; D008297:Male; D012621:Seasons; D012720:Severity of Illness Index