Related Experiment Video
Updated: May 11, 2026
High-throughput Assay to Phenotype Salmonella enterica Typhimurium Association, Invasion, and Replication in Macrophages
Published on: August 11, 2014
Multidrug-resistant Salmonella Typhi among symptomatic and asymptomatic children in informal settlements in Nairobi,
Susan M Kavai1,2, Julius Oyugi3,4, Cecilia Mbae5
1Centre for Microbiology Research, Kenya Medical Research Institute, Nairobi, Kenya. ssnkavai8@gmail.com.
Background:
The emergence and persistence of multidrug-resistant (MDR) Salmonella Typhi (S. Typhi) infections is a significant global health problem. The carrier state of typhoid makes it prudent to conduct routine surveillance for both acute cases and carriers especially those caused by MDR S. Typhi. We report on the prevalence of MDR S. Typhi, resistance phenotypes and antimicrobial resistance genes detected in symptomatic and asymptomatic children living in informal settlements in Nairobi, Kenya.
Methods:
215 archived presumed S. Typhi isolates from stool samples provided by children ≤ 16 years collected from 2013 to 2018 were revived in May, 2022 and confirmed using culture and antisera serotyping. The Kirby Bauer disc diffusion technique was used to test the S. Typhi against 14 antibiotics. The MDR S. Typhi (resistant to ampicillin, chloramphenicol and sulfamethoxazole trimethoprim) which in addition were also resistant to either a cephalosporin or a fluoroquinolone were analyzed for Beta lactams and quinolone resistance genes using polymerase chain reaction.
Results:
A total of 215 isolates were confirmed to be positively S. Typhi; of these, 105 (49%) and 110 (51%) were from symptomatic and asymptomatic children respectively. On average, S. Typhi resistance from asymptomatic and symptomatic children against 1st line drugs was observed at; 77% &70%, ampicillin; 60% & 64%, sulfamethoxazole-trimethoprim, and 45% & 54%, chloramphenicol respectively. Multi drug resistance was observed in 90 (42%) of the isolates, of these, 44 (49%) were isolated from symptomatic and 46 (51%) from asymptomatic children. Fifteen resistance phenotypes (p) were observed with, ampicillin/chloramphenicol/sulfamethoxazole-trimethoprim/nalidixic acid (amp/chl/sxt/na) as the most common among the symptomatic 43/90 (48%) and asymptomatic 55/90 (61%) children. The blaTEM-D, AMR genes were detected in 37/44 (84%) S. Typhi isolates, out of this 18 (49%) were from symptomatic while 19 (51%) were from asymptomatic children respectively.
Conclusion:
The carriage of MDR S. Typhi among the asymptomatic children is concerning as they can act as potential transmitters of the typhoid disease to unsuspecting children. These study findings highlight the need for continued surveillance of antimicrobial resistance and mass immunization of children living in these urban informal areas.
Insights
Multidrug-resistant Salmonella Typhi is prevalent in Kenyan children, with asymptomatic carriers posing a significant transmission risk. Continued surveillance and mass immunization are crucial for controlling typhoid in urban informal settlements.
Area of Science:
- Microbiology and Infectious Diseases
- Public Health and Epidemiology
- Molecular Biology
Background:
- Multidrug-resistant (MDR) Salmonella Typhi (S. Typhi) infections represent a critical global health challenge.
- Typhoid fever's carrier state necessitates routine surveillance for both symptomatic and asymptomatic carriers, particularly those with MDR S. Typhi.
- This study investigates MDR S. Typhi prevalence, resistance patterns, and associated genes in children from Nairobi's informal settlements.
Purpose of the Study:
- To determine the prevalence of MDR S. Typhi in symptomatic and asymptomatic children in Nairobi's informal settlements.
- To identify specific antimicrobial resistance phenotypes and genes present in these S. Typhi isolates.
- To assess the public health implications of MDR S. Typhi carriage in children.
Main Methods:
- Revival and confirmation of 215 archived S. Typhi isolates from stool samples of children aged ≤16 years (2013-2018).
- Antimicrobial susceptibility testing using the Kirby Bauer disc diffusion method against 14 antibiotics.
- Polymerase chain reaction (PCR) analysis for Beta-lactam and quinolone resistance genes in MDR S. Typhi isolates.
Main Results:
- Of 215 confirmed S. Typhi isolates, 105 (49%) were from symptomatic and 110 (51%) from asymptomatic children.
- MDR S. Typhi was found in 90 (42%) isolates, with similar distribution between symptomatic (44) and asymptomatic (46) children.
- The ampicillin/chloramphenicol/sulfamethoxazole-trimethoprim/nalidixic acid resistance phenotype was most common; blaTEM-D and AMR genes were detected in 84% of analyzed MDR isolates.
Conclusions:
- Asymptomatic carriage of MDR S. Typhi in children is a significant concern, potentially facilitating disease transmission.
- High rates of antimicrobial resistance underscore the need for ongoing surveillance of S. Typhi in these populations.
- Mass immunization of children in urban informal settlements is recommended to mitigate typhoid transmission.
Related Concept Videos
01:30Reservoir of Infection
01:18Bacterial Gastroenteritis