of ipaH detection in patients with culture-negative diarrhoea.
However this finding cannot exclude Shigella colonization and,
thus, there may be an alternative etiology for reported diarrhoea
or dysentery episodes in some cases. Second, our health-care
utilization survey indicated that a number of individuals first
saw health-care providers who were not taking part in the
surveillance study. These individuals may have attended hospitals
and clinics participating in the study at a later stage in
their disease. It is not clear what proportion of patients were
thus detected at a later stage. Taking these limitations into
consideration, our adjusted estimates have to be viewed as the
highest potential disease rates.
In Thailand, the most commonly isolated Shigella species
over the past two decades have been S. flexneri (79%) and S.
sonnei (15%) (10–12). Only 4% of isolates were S. dysenteriae,
and 2% were S. boydii. In our survey, S. sonnei was the dominant
Shigella species. Previous studies have indicated that S.
sonnei is dominant in more developed countries (13) so our
findings may be confirming the successful economic transition
in the study area, which is within commuting distance to
Bangkok, Thailand’s highly industrialized capital. In contrast
to our community-based study, S. flexneri infections have been
more frequently detected in hospital-based surveillance studies (10–12, 14). One explanation for this could be that S. flexneri
infections result more frequently in hospitalizations than S.
sonnei infections. The notion that S. sonnei is less virulent than
S. flexneri is supported by the possibly shorter duration of diarrhoea
occurring among patients infected with S. sonnei than
among those with S. flexneri in our study.