Of 37 patients with culture-confirmed shigellosis who
were enrolled between 1 May 2002 and 1 May 2003, 27 (73%)
were followed up until day 90 (Fig. 1). Patients with S. flexneri
infections had diarrhoea for a longer period (median duration =
3 days; 95% CI = 2–6 days) than those with S. sonnei infection
(median = 2 days; 95% CI = 2–6 days), but this difference
was not statistically significant (P = 0.149) (data not shown).
Two of 146 shigellosis patients (aged 25 years and 4 years)
were hospitalized but had uneventful recoveries. Two patients
died: a 33-year-old patient who had been treated for AIDS and
persistent diarrhoea and a 72-year-old patient who died 2 days
after being admitted with dysentery.
Of the 146 Shigella strains isolated during the surveillance
period, 22 (15%) were S. flexneri and the others were S.
sonnei. No S. dysenteriae or S. boydii strains were detected. Of
the 22 S. flexneri isolates, the three most frequently encountered
serotypes were 2a (36%), 1b (23%) and 3b (28%). Of 124 S.
sonnei isolates tested, 111 (90%) were resistant to tetracycline,
94% to co-trimoxazole (trimethoprim–sulfamethoxazole), 6%
to ampicillin, and 2% to chloramphenicol. Of the S. flexneri isolates tested, 21 of 22 (96%) were resistant to tetracycline, and
18 of 20 (90%) were resistant to co-trimoxazole. Altogether,
18 of 20 (90%) S. flexneri isolates were also resistant to ampicillin
in contrast to only 7 of 117 (6%) S. sonnei isolates (P <
0.0001). Similarly 14 of 14 S. flexneri isolates were resistant
to chloramphenicol but only 2 of 95 S. sonnei isolates were
resistant (Table 1).
There was a seasonal pattern of dysentery and episodes
of infection with S. sonnei and S. flexneri (Fig. 4). The yearly
peak of dysentery and S. sonnei incidence followed the hottest
months of the year, April–May, and coincided with the onset
of the rainy season. During the summer months of 2001,
higher numbers of cases of dysentery and S. sonnei were detected
compared with the preceding and following years. The
lowest shigellosis rates were observed during the cooler winter
months, November–March.