  Genital warts are a common and highly contagious sexually transmitted
disease. They have a large economic burden and affect several aspects of
quality of life. Incidence data underestimate the real occurrence of genital
warts because this infection is often under-reported, mostly due to their
specific characteristics such as the asymptomatic course. Genital warts cases
for the analysis were obtained from the catalan public health system database
(SIDIAP) for the period 2009-2016, covering 74\% of the Catalan population.
People under 15 and over 94 years old were excluded from the analysis as the
incidence of genital warts in this population is negligible. This work
introduces a time series model based on a mixture of two distributions, capable
of detecting the presence of under-reporting in the data. In order to identify
potential differences in the magnitude of the under-reporting issue depending
on sex and age, these covariates were included in the model. This work shows
that only about 80\% in average of genital warts incidence in Catalunya in the
period 2009-2016 was registered, although the frequency of under-reporting has
been decreasing over the study period. It can also be seen that the
under-reported issue has a deeper impact on women over 30 years old. The
registered incidence in the Catalan public health system is underestimating the
real burden in almost 10,000 cases in Catalunya, around 23\% of the registered
cases. The total annual cost in Catalunya is underestimated in at least about
10 million Euros respect the 54 million Euros annually devoted to genital warts
in Catalunya, representing 0.4\% of the total budget of the public health
system.
