Factors associated with occurrence of salmonellosis among children living in Mukuru slum, an urban informal settlement in Kenya

Environmental persistence of nontyphoidal Salmonella in an urban informal settlement in Nairobi, Kenya

Non-typhoidal Salmonella (NTS) presents a considerable health threat to children in low-resource settings, where clean water, sanitation, and hygiene are often inadequate. However, the environmental factors influencing NTS persistence and spread remain poorly understood. We utilized a case-control approach to investigate environmental factors associated with NTS infection in children living in Nairobi's informal settlements between August 2022 and July 2023. Stool samples were collected from febrile children, with or without diarrhea, who visited healthcare facilities. The study included 42 laboratory-confirmed NTS-positive cases and 42 NTS-negative children from the same community. Environmental samples, including drinking water, open drains, soil, and household effluent, were collected from both case and control households, in addition to raw sewage from main sewer-line convergence points. Conventional microbiological culture and quantitative Polymerase Chain Reaction techniques were employed for NTS detection, with genomic sequencing used for strain characterization. Environmental samples from case households showed a higher NTS contamination rate of 33.3% (42/126) compared to control households of 7.2% (9/126). Higher odds of NTS infection in children were associated with household environmental factors, particularly exposure to household effluent (OR = 7.7, 95% CI: 2.18-34.82, p = 0.0005), drinking water (OR = 6.4, 95% CI: 1.57-37.76, p = 0.0055), and soil (OR = 5.4, 95% CI: 1.01-54.28, p = 0.0485). Genomic analysis revealed a common strain, Salmonella Enteritidis ST11, in clinical and environmental isolates. These findings highlight the plausible role of the household environment as a reservoir for NTS, perpetuating infection cycles within the community. Addressing this challenge requires a multifaceted approach, including improved sanitation infrastructure, environmental monitoring, and integrated public health interventions to reduce NTS exposure and transmission in high-risk populations.

Exploring the use of solid fuels for cooking and household air pollution in informal settlements through photovoice: The Fuel to Pot study in Ndirande (Malawi) and Mukuru (Kenya)

INTRODUCTION

Worldwide, 2.4 billion people rely on solid fuels such as wood or charcoal for cooking, leading to approximately 3.2 million deaths per year from illnesses attributable to household air pollution. Across Africa, household air pollution generated by solid fuel use accounts for nearly 700,000 deaths each year. Most studies to date have focused either household air pollution exposure, its impacts on particular health outcomes or on the efficacy of mitigation interventions. However, the economic, social, and cultural determinants of household air pollution in Africa are still poorly understood. The purpose of this study was to explore people's experience of using solid fuels for cooking in two informal settlements, Ndirande in Malawi and Mukuru in Kenya, and the associated harms caused by household air pollution.

METHODS

We adopted a community-based participatory method, photovoice, which was conducted with 9 participants in Ndirande and 10 participants in Mukuru. Participants took pictures reflecting their experiences and perceptions of household air pollution harms over a two-week period, and later discussed, sorted and analysed those in a series of meetings. Thematic analysis was used to analyse the data.

RESULTS

With their pictures, participants described fuel stacking and switching behaviours in their communities. They described a mix of charcoal, firewood and other biomass fuels use. They also expressed their awareness and perceptions of the harms caused by smoke when cooking. Participants explained the simple behaviours used by residents to minimize the harms of household air pollution to themselves and within their own household. Other themes explored the roles and responsibilities for procuring fuels in the home, and the stated solutions required to address the issues and manage the transition to cleaner fuels in those informal settlements.

CONCLUSION

This study highlights not only the need to understand the daily life, priorities and concerns of those who use solid fuels on informal settlements, but also the urgency to place them and their experience at the heart of the solutions that will reduce the health harms of household air pollution.

Shedding of nontyphoidal Salmonella by asymptomatic convalescing children under 5 years as a risk factor for invasive disease in Mukuru informal settlement in Nairobi, Kenya

Nontyphoidal Salmonella (NTS) is a predominant cause of invasive disease in sub-Saharan Africa especially among children under 5 years. Asymptomatic fecal shedding of NTS is hypothesized to contribute to the human-to-human transmission of NTS especially in low-resource settings. However, the role of pathogen shedding in invasive disease is unknown. This study aimed to investigate the prevalence and duration of fecal shedding of NTS among children under 5 years convalescing from invasive NTS disease and among healthy individuals in the community. Children presenting with fever of ≥38°C with or without diarrhea were recruited at four health facilities in Nairobi, between June 2021 and August 2023. Blood and stool samples collected were subjected to culture for the isolation of NTS (S. Enteritidis and S. Typhimurium). Children with NTS culture-positive samples (index cases) were followed up post-acute disease where household contacts and controls provided stool samples for isolation of NTS. NTS prevalence among the 3,293 individuals recruited was 1.52%. Asymptomatic shedding post-treatment was observed in almost one-third (31%) of the 42 index cases followed up. Of the 13 with intestinal shedding, 7 were shedding NTS of the same sequence type (ST) as the one recovered during acute disease. The longest duration of intestinal shedding was 3 months post-treatment. Of the 241 healthy individuals recruited, 8 had asymptomatic shedding of NTS, and 2 of these were closely related to those recovered from index cases. These findings support the hypothesis of human-to-human transmission of NTS in sub-Saharan Africa highlighting the possible benefit of vaccine introduction.

IMPORTANCE

Asymptomatic fecal shedding of nontyphoidal Salmonella (NTS) is hypothesized to contribute to the human-to-human transmission of NTS especially in low-resource settings which could lead to invasive disease among high-risk populations, especially children. Our findings reiterate the hypothesis that human reservoirs could be important in the transmission of nontyphoidal Salmonella in sub-Saharan Africa. This underscores the importance of developing infection prevention measures which could include vaccine deployment and improving water, sanitation and hygiene infrastructure.

Virulence, multiple drug resistance, and biofilm-formation in Salmonella species isolated from layer, broiler, and dual-purpose indigenous chickens

Globally, the significant risk to food safety and public health posed by antimicrobial-resistant foodborne Salmonella pathogens is driven by the utilization of in-feed antibiotics, with variations in usage across poultry production systems. The current study investigated the occurrence of virulence, antimicrobial resistant profiles, and biofilm-forming potentials of Salmonella isolates sourced from different chicken types. A total of 75 cloacal faecal samples were collected using sterile swabs from layer, broiler, and indigenous chickens across 15 poultry farms (five farms per chicken type). The samples were analysed for the presence of Salmonella spp. using species-specific PCR analysis. Out of the 150 presumptive isolates, a large proportion (82; 55%) were confirmed as Salmonella species, comprising the serovars S. typhimurium (49%) and S. enteritidis (30%) while 21% were uncategorised. Based on phenotypic antibiotic susceptibility test, the Salmonella isolates were most often resistant to erythromycin (62%), tetracycline (59%), and trimethoprim (32%). The dominant multiple antibiotic resistance phenotypes were SXT-W-TE (16%), E-W-TE (10%), AML-E-TE (10%), E-SXT-W-TE (13%), and AMP-AML-E-SXT-W-TE (10%). Genotypic assessment of antibiotic resistance genes revealed that isolates harboured the ant (52%), tet (A) (46%), sui1 (13%), sui2 (14%), and tet (B) (9%) determinants. Major virulence genes comprising the invasion gene spiC, the SPI-3 encoded protein (misL) that is associated with the establishment of chronic infections and host specificity as well as the SPI-4 encoded orfL that facilitates adhesion, autotransportation and colonisation were detected in 26%, 16%, and 14% of the isolates respectively. There was no significant difference on the proportion of Salmonella species and the occurrence of virulence and antimicrobial resistance determinants among Salmonella isolates obtained from different chicken types. In addition, neither the chicken type nor incubation temperature influenced the potential of the Salmonella isolates to form biofilms, although a large proportion (62%) exhibited weak to strong biofilm-forming potentials. Moderate to high proportions of antimicrobial resistant pathogenic Salmonella serovars were detected in the study but these did not vary with poultry production systems.

Multidrug-resistant Salmonella Typhi among symptomatic and asymptomatic children in informal settlements in Nairobi, Kenya

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.

Genotypic Diversity among Salmonella Typhi Isolated from Children Living in Informal Settlements in Nairobi, Kenya

The persistence of multidrug-resistant (MDR) Salmonella Typhi (S. Typhi) is a challenge especially in regions where typhoid is endemic. Surveillance of circulating genotypes of MDR S. Typhi is crucial in typhoid acute cases and carriers. This study aimed to investigate genotypic diversity of S. Typhi from symptomatic and asymptomatic children in endemic settings in Nairobi, Kenya. Symptomatic and asymptomatic individuals' ≤ 16 years were recruited at four health facilities and tested for typhoid through stool cultures. The S. Typhi isolates were subjected to antibiotic susceptibility testing to investigate multidrug resistance. The MDR S. Typhi isolates' DNA was extracted and illumina sequenced. Raw reads were de novo assembled and analyzed by pathogen-watch. From the 90 sequenced isolates, 60 (67%) were confirmed to be S. Typhi (sequence Type 1 and genotype 4.3.1). Out of the 60 S. Typhi strains; 39 (65%) had plasmids, from these 38 (97%) had IncHI1 plasmids alone. Out of the 60, 59 (98%) S. Typhi isolates had bla TEM-1D . Point mutations conferring reduced susceptibility to quinolones were detected in 42 (70%) of S. Typhi isolates, from these; 14 (33%) had gyrA S83Y, and 28 (67%) gyrB S464F genes, respectively. This study reports 4.3.1 (H58) as the most dominant S. Typhi genotype responsible for spread of MDR phenotypes carried on IncHI1 plasmids. Presence of MDR S. Typhi with resistance genes such as bla TEM-1D and reduced susceptibility to ciprofloxacin especially among asymptomatic individuals, reiterates the need for use of typhoid conjugate vaccine among vulnerable children as a control and prevention measure against typhoid.

Risk Factors for Salmonella Infection in Children under Five Years: A Hospital-Based Study in Kilimanjaro Region, Tanzania

Salmonella is among the causative agents for diarrhea worldwide, but its risk factors in Tanzanian children are poorly understood. A hospital-based cross-sectional study was conducted in Moshi, Kilimanjaro region, from July 2020 to November 2022 among children under five admitted with diarrhea. A questionnaire was administered to all parents/caretakers of the enrolled children. Logistic regression was utilized to analyze the risk factors, with significance at p < 0.05. A total of 306 children were enrolled in the study. The median age was 13.8 months (IQR 8.4-21.8). The majority (58.5%) were males, and 59.5% were from rural areas. Salmonella was identified in eight (2.6%) stool samples, with a higher prevalence in urban than rural areas (4.8% vs. 1.1%; p-value = 0.044). The significant risk factors associated with Salmonella infection among the children included consuming raw milk (adjusted OR = 30.19; 95% CI: 3.94-231.46), using infant formula (adjusted OR = 15.78; 95% CI: 2.98-83.56), undisclosed household income (adjusted OR = 9.98; 95% CI: 2.46-40.12), purchasing eggs direct from the farms (adjusted OR = 7.58; 95%CI: 1.31-43.96), and contact with chickens (adjusted OR = 6.49; 95%CI: 1.25-33.59). These findings highlight the need for targeted interventions to improve food safety, hygiene practices, and socioeconomic conditions.

Identification of Enteric Pathogen Reservoirs and Transmission Pathways Associated with Short Childhood Stature in the Kolkata Indian Site of the Global Enteric Multicenter Study

Age-stratified path analyses modeled associations between enteric pathogen reservoirs, transmission pathways and height-for-age z-scores (HAZ) to identify determinants of childhood growth in the Kolkata, India site of the Global Enteric Multicenter Study (GEMS). Models tested direct associations of potential pathogen reservoirs with HAZ at 60-day follow-up in separate moderate and severe diarrhea (MSD) case and control cohorts or indirectly when mediated by enteric infections. In the MSD cohort, rotavirus and typical EPEC (tEPEC) infections among children 0-11 months of age and ST-ETEC infections among children 12-23 months of age were associated with lower HAZ. Handwashing after defecating and before cooking reduced impaired growth through reductions in rotavirus and tEPEC infections. Water storage increased rotavirus and ST-ETEC infection risks, resulting in increased impaired growth, but was reduced with reported child feces disposal. The GII norovirus variant was inversely associated with HAZ among children 12-59 months of age in the control cohort. Reported handwashing before the handling of children reduced GII infections and impaired growth. Boiling water and the disposal of children's feces mediated by stored water were positively associated with HAZ. The targeting of pathogen-specific reservoirs and transmission pathways may more effectively improve childhood linear growth in South Asian urban communities.

Exploring the antimicrobial efficacy of Manuka honey against multidrug-resistant and extensively drug-resistant Salmonella Typhi causing septicemia in Pakistan

Aim: To determine the efficacy of manuka honey against multidrug-resistant (MDR) and extensively drug-resistant (XDR) clinical strains of Salmonella Typhi.Materials & methods: Clinical isolates were processed using the Bactec blood culture system, identification and antibiogram by Vitek 2 and antibiotic resistance genes through polymerase chain reaction (PCR). Microbroth dilution assays evaluated the antibacterial activity of manuka honey.Results: MDR and XDR-S. Typhi was susceptible to azithromycin. These strains carried the H58, gyrA, gyrB, blaCTX-M-15 , and blaTEM-1 genes. At 100% honey, the zone of inhibition for MDR (15-23 mm) and XDR (15-24 mm) strains. 18/50 MDR and 14/50 XDR strains inhibited at 3.125 v/v% killed at 6.25 v/v% concentration respectively.Conclusion: Manuka honey could be an alternative option for treating S. Typhi infections.

Fecal Shedding, Antimicrobial Resistance and In Vitro Biofilm formation on Simulated Gallstones by Salmonella Typhi Isolated from Typhoid Cases and Asymptomatic Carriers in Nairobi, Kenya

Typhoid fever, caused by the human restricted pathogen Salmonella Typhi, remains a major global public health concern. Even after successful treatment, approximately 3-5% of patients with typhoid fail to clear the bacteria within one year and become chronic carriers. Most typhoid carriers have gallstones in their gallbladder, and biofilm formation on gallstones is highly correlated with chronic carriage. This study's goal was to identify asymptomatic typhoid carriers in an endemic setting in Kenya, and to compare acute versus chronic isolates. A cohort of typhoid fever patients identified through blood and/or stool culture, and their household contacts, were followed up after treatment to detect longitudinal S. Typhi stool shedding. An abdominal ultrasound scan was used to identify individuals with gallstones. A total of 32 index patients and 32 household contacts were successfully followed-up. Gallstones were detected in 4 cases and 1 household contact. The duration of S. Typhi shedding was significantly longer in individuals with gallstones compared to those without, P<0.001. Eighty-three (83) S. Typhi strains were tested for susceptibility to commonly used antimicrobials and examined by in vitro biofilm formation assays. Out of 37 infected individuals, 32.4% had infections caused by multidrug resistant (MDR) S. Typhi strains and only 18.9% were infected by susceptible strains. Non-MDR strains formed significantly better biofilms in vitro than the MDR strains (P<0.001). This study provides data on S. Typhi chronic carriage that will influence public health approaches aimed at reducing typhoid transmission and the burden of infection.

Age-dependent acquisition of IgG antibodies to Shigella serotypes-a retrospective analysis of seroprevalence in Kenyan children with implications for infant vaccination

Background

Shigellosis mainly affects children under 5 years of age living in low- and middle-income countries, who are the target population for vaccination. There are, however, limited data available to define the appropriate timing for vaccine administration in this age group. Information on antibody responses following natural infection, proxy for exposure, could help guide vaccination strategies.

Methods

We undertook a retrospective analysis of antibodies to five of the most prevalent Shigella serotypes among children aged <5 years in Kenya. Serum samples from a cross-sectional serosurvey in three Kenyan sites (Nairobi, Siaya, and Kilifi) were analyzed by standardized ELISA to measure IgG against Shigella sonnei and Shigella flexneri 1b, 2a, 3a, and 6. We identified factors associated with seropositivity to each Shigella serotype, including seropositivity to other Shigella serotypes.

Results

A total of 474 samples, one for each participant, were analyzed: Nairobi (n = 169), Siaya (n = 185), and Kilifi (n = 120). The median age of the participants was 13.4 months (IQR 7.0-35.6), and the male:female ratio was 1:1. Geometric mean concentrations (GMCs) for each serotype increased with age, mostly in the second year of life. The overall seroprevalence of IgG antibodies increased with age except for S. flexneri 6 which was high across all age subgroups. In the second year of life, there was a statistically significant increase of antibody GMCs against all five serotypes (p = 0.01-0.0001) and a significant increase of seroprevalence for S. flexneri 2a (p = 0.006), S. flexneri 3a (p = 0.006), and S. sonnei (p = 0.05) compared with the second part of the first year of life. Among all possible pairwise comparisons of antibody seropositivity, there was a significant association between S. flexneri 1b and 2a (OR = 6.75, 95% CI 3-14, p < 0.001) and between S. flexneri 1b and 3a (OR = 23.85, 95% CI 11-54, p < 0.001).

Conclusion

Children living in low- and middle-income settings such as Kenya are exposed to Shigella infection starting from the first year of life and acquire serotype-specific antibodies against multiple serotypes. The data from this study suggest that Shigella vaccination should be targeted to infants, ideally at 6 or at least 9 months of age, to ensure children are protected in the second year of life when exposure significantly increases.

Intestinal carriage of invasive non-typhoidal Salmonella among household members of children with Salmonella bloodstream infection, Kisangani, DR Congo

Introduction

Invasive non-typhoidal Salmonella (iNTS), mainly Salmonella Typhimurium and Salmonella Enteritidis, causes a severe burden in sub-Saharan Africa; however, its reservoir (animal or environmental) is unclear. The present study assessed healthy household members of index patients for intestinal carriage of Salmonella.

Methods

Index patients were admitted to the University Hospital of Kisangani (DR Congo), and Salmonella was grown from blood cultures. Household members were asked to provide three stool samples for culture for Salmonella. Salmonella Typhimurium and S. Enteritidis isolates from index patients, and household members were assessed for genetic relatedness using the multiple-locus variable number of tandem repeat analysis (MLVA), and the multilocus sequence type (ST) was determined by whole genome sequencing.

Results

Between May 2016 and January 2020, 22 households were visited. The index patient serotypes were Typhimurium, Enteritidis, Typhi, and Paratyphi C; II:42:r:-; and I:7:y:- (n = 8, 7, 5, and each 1, respectively). The median (range) delay between the index patient and household sampling was 25 days (2 days to 7.3 months); 203 household members provided at least one stool sample. In all, 15 (7.3%) Salmonella carriers were found in nine of 22 households. For one index patient, the household comprised S. Typhimurium in four household members, including the index patient, sampled 27 days after bloodstream infection; the MLVA types of these five isolates were similar. They belonged to ST313 lineage 2 and were closely related [0-1 allelic distance (AD) among the stool isolates and eight AD with the blood culture isolate]. In another household, the stool culture of the index patient (obtained 67 days after bloodstream infection) grew S. Enteritidis of the same MLVA type; both isolates belonged to the ST11 Central/Eastern African clade and were closely related (three AD).

Discussion

The present study provides evidence of household clustering of S. Typhimurium ST313 and intestinal carriage of iNTS several weeks after bloodstream infection.

The epidemiology of fecal carriage of nontyphoidal Salmonella among healthy children and adults in three sites in Kenya

BACKGROUND

Despite the importance of non-Typhoidal Salmonella (NTS) disease in Africa, epidemiologic data on carriage and transmission are few. These data are important to understand the transmission of NTS in Africa and to design control strategies.

METHOD

To estimate the prevalence of stool carriage of NTS in Kenya, we conducted a cross-sectional study in Kilifi, Nairobi, and Siaya, sites with a low, moderate and high incidence of invasive NTS disease, respectively. At each site, we randomly selected 100 participants in each age-group of 0-11 months, 12-59 months, 5-14 years, 15-54 years and ≥55 years. We collected stool, venous blood (for hemoglobin and malaria rapid tests), anthropometric measurements, and administered a questionnaire on Water Access Sanitation and Hygiene (WASH) practices. Stool samples were cultured on selective agar for Salmonella; suspect isolates underwent serotyping and antimicrobial susceptibility testing.

RESULT

Overall, 53 (3.5%) isolates of NTS were cultured from 1497 samples. Age-adjusted prevalence was 13.1% (95%CI 8.8-17.4) in Kilifi, 0.4% (95%CI 0-1.3) in Nairobi, and 0.9% (95%CI 0-2.0) in Siaya. Prevalence was highest among those aged 15-54 years (6.2%). Of 53 isolates; 5 were S. Enteritidis, 1 was S. Typhimurium. No S. Typhi was isolated. None of the risk factors were associated with carriage of NTS. All isolates were susceptible to all antibiotics tested, including ampicillin, chloramphenicol, ciprofloxacin and co-trimoxazole.

CONCLUSION

Prevalence of fecal carriage was high in Kilifi, an area of low incidence of invasive NTS disease and was low in areas of higher incidence in Nairobi and Siaya. The age-prevalence, risk factors, geographical and serotype distribution of NTS in carriage differs from invasive disease.

Seroprevalence of non-typhoidal Salmonella disease and associated factors in children in Mukuru settlement in Nairobi County, Kenya

Non-typhoidal Salmonella (NTS) infections remain a significant public health challenge especially in sub-Saharan Africa. NTS disease is endemic in Kenya and is associated with sporadic fatal outbreaks in several regions of the country with poor resource setting. Data is limited on background exposure of NTS in the population in endemic areas and the general immune status of the community most affected by NTS. The aim of the study was to determine the proportion of children exposed to Salmonella Enteritidis or Salmonella Typhimurium O antigen among the apparently healthy children and patients and the associated host and environmental factors among children attending selected healthcare facilities in Mukuru, Nairobi County, Kenya. A cross-sectional case-control study was conducted among patients and apparently healthy participants aged 0-5 years. Blood was collected and centrifuged to obtain serum. The serum was used to test for the presence of antibodies (IgA, IgG, IgM) against NTS using ELISA. A questionnaire was administered to obtain relevant demographic, socio-economic and healthcare utilization information. A total of 382 children were recruited into the study. The NTS seroprevalence was 12.6%. Among the apparently healthy participants, mean age of those exposed to NTS was 36 months and those not exposed was 27 months. Among patients, the mean age was 39 months and those not exposed was 30 months. The seroprevalence of NTS infection among the apparently healthy was significantly associated with cooking water, washing water and age of the child. Treating water using chlorine or boiling method was identified as being protective against contracting Salmonella Typhimurium/Enteritidis. Among the patients, the proportion of exposure was significantly associated with keeping animals and the chicken count. There is a high exposure to NTS among young children below five years of age and the population has developed immunity to the disease.

Human Salmonellosis: A Continuous Global Threat in the Farm-to-Fork Food Safety Continuum

Salmonella is one of the most common zoonotic foodborne pathogens and a worldwide public health threat. Salmonella enterica is the most pathogenic among Salmonella species, comprising over 2500 serovars. It causes typhoid fever and gastroenteritis, and the serovars responsible for the later disease are known as non-typhoidal Salmonella (NTS). Salmonella transmission to humans happens along the farm-to-fork continuum via contaminated animal- and plant-derived foods, including poultry, eggs, fish, pork, beef, vegetables, fruits, nuts, and flour. Several virulence factors have been recognized to play a vital role in attaching, invading, and evading the host defense system. These factors include capsule, adhesion proteins, flagella, plasmids, and type III secretion systems that are encoded on the Salmonella pathogenicity islands. The increased global prevalence of NTS serovars in recent years indicates that the control approaches centered on alleviating the food animals' contamination along the food chain have been unsuccessful. Moreover, the emergence of antibiotic-resistant Salmonella variants suggests a potential food safety crisis. This review summarizes the current state of the knowledge on the nomenclature, microbiological features, virulence factors, and the mechanism of antimicrobial resistance of Salmonella. Furthermore, it provides insights into the pathogenesis and epidemiology of Salmonella infections. The recent outbreaks of salmonellosis reported in different clinical settings and geographical regions, including Africa, the Middle East and North Africa, Latin America, Europe, and the USA in the farm-to-fork continuum, are also highlighted.

Complementary measurement of nontyphoidal Salmonella-specific IgG and IgA antibodies in oral fluid and serum

Objectives

Immuno-epidemiological studies of orally acquired, enteric pathogens such as nontyphoidal Salmonella (NTS) often focus on serological measures of immunity, ignoring potentially relevant oral mucosal responses. In this study we sought to assess the levels and detectability of both oral fluid and serum IgG and IgA to NTS antigens, in endemic and non-endemic populations.

Methods

IgG and IgA antibodies specific for Salmonella Typhimurium and Salmonella Enteritidis O antigen and phase 1 flagellin were assessed using Enzyme Linked Immunosorbent Assay (ELISA). Paired oral fluid and serum samples were collected from groups of 50 UK adults, Kenyan adults and Kenyan infants. Additionally, oral fluid alone was collected from 304 Kenyan individuals across a range of ages.

Results

Antigen-specific IgG and IgA was detectable in the oral fluid of both adults and infants. Oral fluid antibody increased with age, peaking in adulthood for both IgG and IgA but a separate peak was also observed for IgA in infants. Oral fluid and serum responses correlated for IgG but not IgA. Despite standardised collection the relationship between oral fluid volume and antibody levels varied with age and country of origin.

Conclusions

Measurement of NTS-specific oral fluid antibody can be used to complement measurement of serum antibody. For IgA in particular, oral fluid may offer insights into how protective immunity to NTS changes as individuals transition with age, from maternal to acquired systemic and mucosal immunity. This may prove useful in helping to guide future vaccine design.

Case-control investigation of invasive Salmonella disease in Malawi reveals no evidence of environmental or animal transmission of invasive strains, and supports human to human transmission

BACKGROUND

Invasive Salmonella infections cause significant morbidity and mortality in Sub-Saharan Africa. However, the routes of transmission are uncertain. We conducted a case-control study of index-case and geographically-matched control households in Blantyre, Malawi, sampling Salmonella isolates from index cases, healthy people, animals, and the household environment.

METHODOLOGY

Sixty index cases of human invasive Salmonella infection were recruited (March 2015-Oct 2016). Twenty-eight invasive Non-Typhoidal Salmonella (iNTS) disease and 32 typhoid patients consented to household sampling. Each index-case household was geographically matched to a control household. Extensive microbiological sampling included stool sampling from healthy household members, stool or rectal swabs from household-associated animals and boot-sock sampling of the household environment.

FINDINGS

1203 samples from 120 households, yielded 43 non-Typhoidal Salmonella (NTS) isolates from 25 households (overall sample positivity 3.6%). In the 28 iNTS patients, disease was caused by 3 STs of Salmonella Typhimurium, mainly ST313. In contrast, the isolates from households spanned 15 sequence types (STs). Two S. Typhimurium isolates from index cases closely matched isolates from their respective asymptomatic household members (2 and 3 SNP differences respectively). Despite the recovery of a diverse range of NTS, there was no overlap between the STs causing iNTS disease with any environmental or animal isolates.

CONCLUSIONS

The finding of NTS strains from index cases that matched household members, coupled with lack of related animal or environmental isolates, supports a hypothesis of human to human transmission of iNTS infections in the household. The breadth of NTS strains found in animals and the household environment demonstrated the robustness of NTS sampling and culture methodology, and suggests a diverse ecology of Salmonella in this setting. Healthy typhoid (S. Typhi) carrier state was not detected. The lack of S. Typhi isolates from the household environment suggests that further methodological development is needed to culture S. Typhi from the environment.

Typhoid in Pakistan: Challenges, Efforts, and Recommendations

Typhoid, and its extra drug resistant form which is highly prevalent Pakistan, is increasing the burden on healthcare through multiple factors. These range from lack of sanitation, the collapsing economy, and poor access to clean drinking water which have made it arduous for the government and various other organizations in containing it. With the COVID-19 pandemic, treatment of typhoid became a challenge as focus was driven towards limiting the COVID-19 spread, and hence preferential use of antibiotics such as azithromycin may limit future empirical antibiotic therapy for typhoid. Socioeconomic disparities and geographical as well as demographic barriers further limit access to appropriate typhoid management. Lastly, illiteracy and self-medication with antibiotics may predispose Pakistan to another outbreak of typhoid. These concerns, although largely unaddressed effectively, need immediate action. Previously, the government and international organizations have made efforts to control the spread through the introduction of TCV as a part of EPI and awareness, additional improvements are needed. These include: improving access to telemedicine in rural areas, extensive vaccination programs, and routine awareness programs especially in schools.

Out-of-pocket payment for healthcare among urban citizens in Dhaka, Bangladesh

Objectives

Out-of-pocket (OOP) payment is the major payment strategy for healthcare in Bangladesh, and the share of OOP expenditure has increased alarmingly. Dhaka is recognised as one of the fastest-growing megacities in the world. The objective of this study is to capture the self-reported illnesses among urban citizens and to identify whether and to what extent socioeconomic, demographic and behavioural factors of the population influence OOP healthcare expenditures.

Subject and methods

This study utilises cross-sectional survey data collected from May to August 2019 in urban Dhaka, Bangladesh. A total of 3,100 households were randomly selected. Simple descriptive statistics including frequencies, percentage, mean (95% CI), median and inter-quartile range were presented. Bivariate analysis and multivariate regression models were employed.

Results

We observed that acute illnesses (e.g., fever, flu/cough) were dominant among participants. Among the chronic illnesses, approximately 9.6% of people had diabetes, while 5.3% had high/low blood pressure. The richest quintile only spent 5.2% of their household income on healthcare, while the poorest households spent approximately six times more than the richest households. We noted that various factors such as marital status, religion, source of care, access to safe water, income quintile and even the location of households had a significant relationship with OOP expenditure.

Conclusions

Our findings can serve as important source of data in terms of disease- specific symptoms and out-of-pocket cost among urban citizens in Dhaka. The people belonging to wealthier households tended to choose better healthcare facilities and spend more. A pro-poor policy initiative and even an urban health protection scheme may be necessary to ensure that healthcare services are accessible and affordable, in line with the Bangladesh National Urban Health Strategy.

Multiple introductions of multidrug-resistant typhoid associated with acute infection and asymptomatic carriage, Kenya

Background:

Understanding the dynamics of infection and carriage of typhoid in endemic settings is critical to finding solutions to prevention and control.

Methods:

In a 3-year case-control study, we investigated typhoid among children aged <16 years (4670 febrile cases and 8549 age matched controls) living in an informal settlement, Nairobi, Kenya.

Results:

148 S. Typhi isolates from cases and 95 from controls (stool culture) were identified; a carriage frequency of 1 %. Whole-genome sequencing showed 97% of cases and 88% of controls were genotype 4.3.1 (Haplotype 58), with the majority of each (76% and 88%) being multidrug-resistant strains in three sublineages of the H58 genotype (East Africa 1 (EA1), EA2, and EA3), with sequences from cases and carriers intermingled.

Conclusions:

The high rate of multidrug-resistant H58 S. Typhi, and the close phylogenetic relationships between cases and controls, provides evidence for the role of carriers as a reservoir for the community spread of typhoid in this setting.

Funding:

National Institutes of Health (R01AI099525); Wellcome Trust (106158/Z/14/Z); European Commission (TyphiNET No 845681); National Institute for Health Research (NIHR); Bill and Melinda Gates Foundation (OPP1175797).

Entamoeba species infection in patients seeking treatment for diarrhea and abdominal discomfort in Mukuru informal settlement in Nairobi, Kenya

Entamoeba histolytica is the only pathogenic species of the Entamoeba genus and is morphologically identical to E. dispar/E. moshkovskii (Entamoeba complex) hence cannot be microscopically differentiated. The other Entamoeba spp. found in humans (E. hartmanni, E. polecki, and E. coli) can be differentiated morphologically from this Entamoeba complex. However, some of their morphologic features overlap making differential diagnosis difficult. This study aimed at determining the occurrence of Entamoeba spp. in patients seeking treatment for diarrhea and/or abdominal discomfort at two clinics in Mukuru informal settlement in Nairobi, Kenya. Faecal samples were collected from 895 patients, examined microscopically following direct wet smear and formal-ether concentration methods. Entamoeba spp. positive faecal samples were subjected to DNA extraction and species-specific nested polymerase chain reaction of the 18S ribosomal RNA (rRNA). By microscopy, Entamoeba spp. cysts or trophozoites were detected in 114/895 (12.7%, 95% Confidence Interval (CI) 10.6-15.1) faecal samples. By nested PCR, the prevalence was: E. histolytica (7.5%, 95% CI 5.9-9.4, 67/895) and E. dispar (8.2%, 95% CI 6.5-10.2, 73/895). Among the Entamoeba spp. complex positive samples, nested PCR detected E. coli and E. hartmanni DNA in 63/114 (55.3%) and 37/114 (32.5%), samples respectively. Among the E. histolytica/E. dispar PCR negative samples (32.5%), 21 (18.4%) contained cysts of either E. coli (19) or E. hartmanni (2) by nested PCR. Entamoeba spp. infections were most common among participants aged 21-30 years; however it was not significant (P = 0.7). Entamoeba spp. infections showed an inverse relationship with diarrhea being most common among participants without diarrhea (P = 0.0). The difference was significant for E. histolytica (P = 0.0) but not significant for E. dispar (P = 0.1). Only E. dispar infections were significantly associated with sex (P = 0.0). This study highlights the need for differentiation of E. histolytica from other Entamoeba spp. by molecular tools for better management of amoebiasis.