title: Intrafamilial person-to-person spread of bacillary dysentery due to Shigella dysenteriae in southwestern Saudi Arabia.
abstract: OBJECTIVE
  To identify the factors that influence transmission of bacillary dysentry (BD) within families during a propagated outbreak of bacillary dysentery.
  
  
  METHODS
  A retrospective cohort study.
  
  
  METHODS
  Eighteen neighbouring villages in rural Gizan, southwestern Saudi Arabia.
  
  
  METHODS
  Two hundred and thirty three cases of BD were identified among seventy nine families.
  
  
  RESULTS
  Secondary cases of BD occurred in 57 of 79 families with a primary case of BD. The secondary attack rate per cent (AR%) within families ranged between 7.7% and 80%. Age of primary cases did not correlate with degree of secondary AR% in exposed families (p > 0.04; p > 0.05); however, within households, the age of the first secondary cases (median = two years) was usually less than the age of the primary case (median = six years). Children under five years of age constituted 43% of secondary cases. The median interval between successive cases within a house ranged from three and seven days. Two hundred and twenty cases (94.4%) gave history of close contact within another case of BD. Cases of BD were exposed to close relatives with BD (79.1%), neighbours (11.4%), and friends (9.5%). Risk factors influencing the spread of BD within families included two rooms or fewer per house (OR = 4.3, 9.5% CI 1.3-14.3), family size of five or more (p = 0.012, two-tailed Fisher's exact test), and presence of more than two persons per room (OR = 11.2, 95% CI 3.1-42.4).
  
  
  CONCLUSIONS
  Person-to-person secondary transmission can amplify the spread of bacillary dysentery within households and neighbouring villages. Crowding was a risk factor that amplified transmission of BD within families.
authors.affiliation: Saudi Arabian Field Epidemiology Training Program Riyadh, Kingdom of Saudi Arabia.
authors.forename: H E
authors.initials: HE
authors.lastname: el Bushra
authors.forename: A A
authors.initials: AA
authors.lastname: Bin Saeed
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D002648:Child; D002675:Child, Preschool; D003441:Crowding; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D004405:Dysentery, Bacillary / Q000453:epidemiology* / Q000382:microbiology / Q000635:transmission*; D005190:Family; D005191:Family Characteristics; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D011159:Population Surveillance; D012189:Retrospective Studies; D012307:Risk Factors; D012529:Saudi Arabia / Q000453:epidemiology; D017678:Sex Distribution; D012762:Shigella dysenteriae; D013997:Time Factors