Salmonellosis in Lagos, Nigeria: Incidence of Plasmodium falciparum
-associated Co-infection, Patterns of Antimicrobial Resistance, and
Emergence of Reduced Susceptibility to Fluoroquinolones
The present study was undertaken to examine the status of antimicrobial
resistance in Salmonella-associated diseases, by verifying possible
emergence of reduced susceptibility to fluoroquinolones in Salmonella
isolates and determining the incidence of Plasmodium falciparum
-associated co-infection with Salmonella serotypes. Antimicrobial
resistance in clinical isolates of Salmonellae was examined for a
12-month period. Four hundred and forty-one patients comprising two
groups were recruited. Group A comprised 235 patients diagnosed by
clinicians of having pyrexia, and group B included stool samples of 206
patients presenting with gastroenteritis. Samples were cultured and
isolates identified, and drug susceptibility testing was performed
using the standard methods. Of the 235 samples screened in group A, 42
Salmonella isolates and 107 Plasmodium spp. were identified. Of the 42
Salmonella isolates, 19 (45.2%) were Salmonella Typhi, 9 (21.4%) S.
Enteritidis, and 7 (16.7%) each of S. Paratyphi and S. Arizonae.
Plasmodium spp.-associated co-infection with Salmonellae was observed
in 16 patients mostly in complicated typhoidal cases and S.
Enteritidis-associated bacteraemia. Fiftty-three of the 206 stool
samples from group B patients were confirmed positive for bacterial
pathogens, made up of 35 Salmonella and 18 Shigella isolates. Of the
Salmonella isolates, 18 (51.4%) were S. Enteritidis, 11 (31.4%) S.
Arizonae, 4 (11.4%) S. Paratyphi, and 2 (5.7%) S. Typhi. There was no
statistically significant difference (p<0.01) in antimicrobial
resistance patterns exhibited among typhoidal Salmonellae isolated in
2000 and 2005. A similar trend in resistance was recorded for
non-typhoidal Salmonellae (p<0.05). For the first time in Lagos,
Nigeria, Salmonella isolates (10-18%) with reduced susceptibility to
both ciprofloxacin and ofloxacin at MIC50 and MIC90 values of 0.015 and
0.03 \ub5g/mL respectively were found. Despite this development,
ciprofloxacin and ofloxacin remain the drug of choice for severe cases
of salmonellosis, although caution should be exercised by clinicians in
their prescriptions such that fluoroquinolone antibiotic therapy is
used only in laboratory-proven cases of typhoid fever and
Salmonella-associated bacteraemia to preserve its efficacy