Results
All 505 women contributed four study visits each over the
1st year; however, there were missing samples for
eight women (1.6%) at the 4-month visit and for twelve women (2.4%) at
the 8-month visit, for a final total of 2000 study visits with samples.
All available samples were valid (positive for either β-globin or HPV).
Baseline characteristics of the subcohort have previously been
reported;19 the mean age was 33.5 years (range:
18–57) and most women were married (49%) or living as married (33%).
There were 281/2000 (14%) samples positive for any betapapillomavirus
across all study visits. The prevalence and incidence of individual
betapapillomaviruses are presented in Table 1. The most prevalent and
incident types were HPV38, HPV21, HPV5, HPV22, and HPV8, respectively;
these were the only types with a time-averaged prevalence above 1%.
We observed significant clustering within HPV genera (Table 2). Over the
four visits, we observed 44 samples positive for two or more
alphapapillomavirus types, and 56 samples positive for two or more
betapapillomavirus types. This represents respectively 1.74 (95%CI
1.26-2.44) times more alphapapillomavirus type co-detections than
expected and 2.24 (95%CI 1.65-3.29) times more betapapillomavirus type
co-detections than expected when assuming independence of types. The
betapapillomavirus types most often found in co-detection with others
were also the most commonly detected types (HPV 38, HPV21, HPV5, HPV22,
and HPV8).
Conversely, there were fewer than expected co-detections of
alphapapillomaviruses and betapapillomaviruses (Table 2). Over the four
visits, we observed 33 samples positive for both an alphapapillomavirus
and a betapapillomavirus type together. This represents 0.64 (95%CI
0.51-0.83) times fewer cross-genus co-detections than expected when
assuming independence of all types. After accounting for the
within-genus expected clustering of both genera, this represented 0.80
(95%CI 0.62-1.06) times fewer cross-genus detections than expected when
assuming cross-genus independence.
Cross-sectional and prospective associations between betapapillomavirus
positivity, alphapapillomavirus positivity, and sexual risk factors are
presented in Table 3 and Table 4. Samples were somewhat less likely to
be positive for alphapapillomavirus types if a betapapillomavirus type
was present (OR 0.73, 95%CI 0.50-1.07). They were also somewhat less
likely to be positive for betapapillomavirus types if an
alphapapillomavirus type was present (OR 0.79, 95%CI 0.56-1.12), but
neither of these associations were significant. Women were also less
likely to become newly positive for alphapapillomavirus types if a
betapapillomavirus type was present at the previous visit (HR 0.84,
95%CI 0.49-1.43), and were less likely to become newly positive for
betapapillomavirus types if an alphapapillomavirus type was present at
the previous visit (HR 0.72, 95%CI 0.45-1.15), but these associations
were also not significant. Alphapapillomavirus prevalence and incidence
were strongly associated with age, increasing lifetime number of sex
partners, and having new sex partners in the previous interval.
Conversely, betapapillomavirus prevalence and incidence were not
associated with age, and were inversely correlated with the number of
lifetime sex partners. While having a new sex partner in the previous
interval was not associated with prevalence or incidence, having sex
with any partner in the previous interval was associated with a higher
incidence of betapapillomavirus (HR 1.56, 95%CI 1.00-2.46).
Multivariable adjustment did not change these associations.