title: Seasonal variation in acute gouty arthritis: data from Nationwide Inpatient Sample.
abstract: BACKGROUND
  Studies describing seasonal variations in acute gouty arthritis note seasonal variation, but disagree on timing, with most showing a peak in spring months while others show peaks later in the year. Various theories on the effect of weather and immune system changes on the chronobiology of monosodium urate crystals' equilibrium and precipitation have been proposed. We aimed to shed light on this question by examining the seasonal variation in the incidence of acute gouty arthritis in the USA using a large inpatient database.
  
  
  METHODS
  We used the Nationwide Inpatient Sample (NIS) database to identify patients aged ≥18 years with primary diagnosis of acute gouty arthritis (International Classification of Diseases, 9th Revision, Clinical Modification code 274.01) from 2009-2011 during hospitalization. We used the Edwards recognition and estimation of cyclic trend method to study the seasonal variation of the incidence of acute gout and z-test to compare the seasonal incidences.
  
  
  RESULTS
  A total of 28,172 hospitalizations with primary diagnosis of acute gouty arthritis were reported in the USA from 2009-2011. The peak incidence of acute gout was seen in November (peak/low ratio 1.34, 95 % CI 1.29-1.38, p < 0.05). The highest number of hospitalizations was observed in autumn months while the lowest incidence was observed in spring (28.12 vs. 23.13 %, p < 0.001).
  
  
  CONCLUSIONS
  The peak incidence of acute gout seems to be in the fall with its peak in the month of November. This seasonality may shed light into the pathophysiology of acute attacks and better management of patients with gout who are at risk of acute attacks.
authors.affiliation: Department of Internal Medicine, Reading Health System, 6th Avenue and Spruce Street, West Reading, PA, USA.
authors.forename: Paras
authors.initials: P
authors.lastname: Karmacharya
authors.affiliation: Department of Internal Medicine, Reading Health System, 6th Avenue and Spruce Street, West Reading, PA, USA. ranjanrp@gmail.com.
authors.forename: Ranjan
authors.initials: R
authors.lastname: Pathak
authors.affiliation: Department of Internal Medicine, Reading Health System, 6th Avenue and Spruce Street, West Reading, PA, USA.
authors.forename: Madan Raj
authors.initials: MR
authors.lastname: Aryal
authors.affiliation: Department of Internal Medicine, University of Tennessee Health Science Center, Memphis, TN, USA.
authors.forename: Smith
authors.initials: S
authors.lastname: Giri
authors.affiliation: Department of Internal Medicine, Reading Health System, 6th Avenue and Spruce Street, West Reading, PA, USA.
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Donato
mesh_terms: D015210:Arthritis, Gouty / Q000453:epidemiology*; D006801:Humans; D012621:Seasons; D014481:United States / Q000453:epidemiology
keywords: Arthritis; Gout; Gouty; HCUP; NIS; Seasons