title: Two-week versus six-month sampling interval in a short-term natural history study of oral HPV infection in an HIV-positive cohort.
abstract: BACKGROUND
  Oral HPV infections detected six-months apart were compared to those detected bi-weekly, in an HIV-positive cohort, during the intervening months to elucidate systematic biases introduced into natural history studies by sampling interval.
  
  
  METHODS
  Fourteen consecutive oral rinse samples were collected every two weeks for six months from an HIV-positive cohort (n = 112) and evaluated for the presence of 37 HPV types. The cumulative probability of type-specific HPV detection at visits 1 through 14 was determined as a function of infection categorized at visits 1 and 14 as persistent, newly detected, cleared or absent. Transition models were used to evaluate the effect of HPV viral load (measured by RT-PCR for HPV 16, 18, 31, 33, 35) on infection persistence.
  
  
  RESULTS
  The average point prevalence of oral HPV infection was similar at two-week and six-month sampling intervals (45% vs. 47%, p = 0.52), but cumulative prevalence was higher with the former (82% vs. 53%, p<0.001) as was the cumulative prevalence of type-specific infections (9.3% vs 3.8%, p<0.0001). Type-specific infections persistent under a six-month sampling interval had a high probability (0.93, 95%CI 0.83-0.98) of detection at 50% or more of the intervening visits and infections that were absent had a high probability (0.94, 95% CI 0.93-0.95) of no interval detection. The odds of detection at any visit significantly increased for each unit increase in HPV viral load at the previous visit.
  
  
  CONCLUSIONS
  Six-month sampling is appropriate to model factors associated with type-specific oral HPV infection persistence but may misclassify HPV-exposed individuals as unexposed.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins Hospital, Baltimore, Maryland, United States of America.
authors.forename: Carole
authors.initials: C
authors.lastname: Fakhry
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Sugar
authors.forename: Gypsyamber
authors.initials: G
authors.lastname: D'Souza
authors.forename: Maura
authors.initials: M
authors.lastname: Gillison
mesh_terms: D000328:Adult; D005260:Female; D015658:HIV Infections / Q000150:complications / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009059:Mouth Diseases / Q000821:virology*; D030361:Papillomavirus Infections / Q000453:epidemiology* / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D011795:Surveys and Questionnaires