Introduction
Progression from anorectal abscess to fistula is po
orly described and it remains unclear
which patients develop a fistula following a preced
ing abscess. We aim to assess the burden
of anorectal abscess and the risk factors of subseq
uent fistula formation.
Methods
The Hospital Episode Statistics database was used t
o identify all patients presenting with
new anorectal abscesses. Cox regression analysis wa
s undertaken to identify factors
predictive of fistula formation.
Results
159,052 patients in England with first-time abscess
es presented from 1997-2012 with an
incidence rate of 20.2/100,000. Subsequent fistula
formation following an abscess was
16.0% (25,530/159,563) in idiopathic cases and 41.5
% (4,407/10,613) in IBD cases (27%
coded concurrently as ulcerative colitis (UC); 47.0
% coded as Crohn’s disease (CD)). Of the
total patients who developed a fistula, 67.0% did s
o within the first year.
Independent predictors of fistula formation were;
IBD
, in particular
CD
(HR 3.51, p<0.001),
UC
(HR 1.82, p<0.001),
female gender
(HR 1.18, p<0.001),
41-60 years old
(HR 1.85, p<0.001,
compared to the <20 age group); and
intersphincteric
(HR 1.53, p<0.001) or
ischiorectal
(HR
1.48, p<0.001) abscess locations, compared to peria
nal.
2.8% of all patients presenting with a new abscess
were subsequently diagnosed with CD
(median 14 months).
Conclusion
This population study demonstrates that the burden
of anorectal sepsis is high, with
subsequent fistula formation nearly x3 times higher
in CD than idiopathic disease. Female
gender is a novel, independent predictor of fistula
formation following abscess drainage and
most fistulas form within the first year. Risk stra
tification can guide management and
follow-up.