Antibiotic resistance of faecal Escherichia coli from healthy volunteers from eight developing countries

OBJECTIVES

To determine the prevalence of antibiotic-resistant faecal Escherichia coli from adult volunteers from urban (U) areas in Kenya, Mexico, Peru and the Philippines, and non-urban (NU) locations in Curacao, Mexico, Venezuela, Ghana, Zimbabwe and the Philippines.

METHODS

Faecal samples of adult volunteers (n=1290) were analysed in one laboratory for the presence of antimicrobial-resistant E. coli using Eosin Methylene Blue agar plates containing, respectively, ampicillin, oxytetracycline, cefazolin, ciprofloxacin, gentamicin, chloramphenicol and trimethoprim at breakpoint concentrations.

RESULTS

The mean age of the volunteers was approximately 35 years; most of them were female. Ciprofloxacin resistance was in the range 1%-63%: the highest percentages were found in the urban populations of Asia and South America. In Peru and the Philippines (U and NU), the prevalence of gentamicin resistance was >20%. Cefazolin resistance was the highest in the urban Philippines (25%). Higher prevalences for ampicillin, oxytetracycline and trimethoprim were found for urban areas compared with non-urban ones of Asia, Africa and South America, respectively (P<0.05).

CONCLUSIONS

In the populations studied, antibiotic resistance in faecal E. coli from adult volunteers was emerging for cefazolin, gentamicin and ciprofloxacin and was high for the older drugs ampicillin, oxytetracycline, trimethoprim and chloramphenicol.

Antimicrobial susceptibility in community-acquired bacterial pneumonia in adults

OBJECTIVES

To determine the antimicrobial susceptibility patterns of Streptococcus pneumoniae and Haemophilus influenzae, two bacterial pathogens commonly associated with community-acquired pneumonia.

DESIGN

Cross-sectional study.

SETTING

Bacterial isolates were obtained from adults suspected to have community-acquired pneumonia and who sought treatment at two city council clinics in Nairobi, Kenya. Susceptibility to antimicrobial agents was performed using a microdilution broth method, according to the criteria set by the National Committee for Clinical Laboratory Standards.

RESULTS

A total of 277 S. pneumoniae and 58 H. influenzae were obtained from 536 adults examined in the period January 1998 to December 1999. Of the 277 S. pneumoniae, only 56.7% were susceptible to penicillin and 7.6% of strains were resistant to two or more antimicrobial agents. Of the 58 H. influenzae strains, 91.4% were sensitive to ampicillin, with 6.8% resistant to two or more antimicrobial agents. 8.6% were beta-lactamase producers and accounted for the entire ampicillin-resistant population.

CONCLUSION

The prevalence of resistance to penicillin and other commonly used antibiotics among pneumococci is high and the large number of multi-resistant strains among H. influenzae is a cause for concern. The prudent use of antibiotics in treatment of pneumonia and other infections should be advocated to minimise spread of resistance.

Non-typhi salmonella in children with severe malaria

OBJECTIVE

To determine the association between Plasmodium falciparum malaria and non-typhi Salmonella in children.

DESIGN

Cross-sectional hospital based study.

SETTING

Kilifi District Hospital (KDH) between January 1997 and June 2001.

SUBJECTS

Children aged between three months to 123 months (mean age 28.28 months) and who had been admitted to the paediatric or High Dependency Research Ward (HDRW) of the KDH.

METHODS

A total of 19, 118 blood cultures routinely obtained for all admissions and 1,820 clinically indicated stools samples were obtained from 9,147 children admitted with malaria. The specimens were cultured and antibiotic sensitivity done using standard laboratory procedures with stringent internal and external quality control in place.

RESULTS

The total bacterial pathogens isolated from blood and stool were 1,395/19,118 (7.3%) and 342/1,820 (19%) respectively. Non-typhi salmonella consisted of 260/1,395 (18.6%) of the positive blood cultures and 92/324 (28.4%) of the stool cultures out of which a total of 101 NTS occurred in children with severe malaria. Out of the 9,147 malaria cases admitted, 101/9,147 (1.10%) had concomitant NTS infection. NTS with severe malaria as a proportion of all malaria admissions for the period varied between 0.8% and 1.5%. There was a significant association (p-value=0.032) between clinical outcome of death and female sex of the patient. The NTS isolates which occurred with severe malaria showed various levels of antibiotic resistance. They were resistant to ampicillin (35%), chloramphenicol (18%), gentamicin (22%), cefuroxime (29%), sulphamethoxazole-trimethoprim (39%), ciprofloxacin (3%), cefotaxime (14%), amoxycillin-clavulanic acid (26%) and tobramycin (18.0%). Multidrug resistance (MDR) was seen in 34 (33.6%) of the isolates.

CONCLUSIONS

NTS and severe malaria occurring together are a problem in this area and that a large number of the isolates are MDR. An elaborate case-controlled study is required to elucidate the chain of events of both NTS and malaria parasite co-existence.

Carriage of Potentially Pathogenic Escherichia coli in Chickens

DNA-DNA hybridization, cultured cell lines, and transmission electron microscopy were used to study pathogenicity traits of 64 Escherichia coli isolated from apparently healthy chickens from 18 small-scale farms in Thika District, Kenya. A total of 39 (60.9%) isolates hybridized with the eae gene probe for enteropathogenic E. coli (EPEC) whereas another 16 (25%) hybridized with the lt and st gene probes and were categorized as enterotoxigenic E. coli. Electron microscopic examination of the eae probe-positive E. coli cultures with the HT-2919A cell line confirmed that they were able to attach intimately and produced effacement typical of EPEC. In addition, negative stain electron microscopy showed that the EPEC strains produced pili that have previously been associated with increased virulence of E. coli infections in chickens. This study has also demonstrated that apparently healthy chickens may carry enteropathogenic E. coli strains.

Antibody responses to repetitive epitopes of the circumsporozoite protein, liver stage antigen-1, and merozoite surface protein-2 in infants residing in a Plasmodium falciparum-hyperendemic area of western Kenya. XIII. Asembo Bay Cohort Project

The present study was initiated to characterize antibody responses to repetitive epitopes of the circumsporozoite protein (CSP), liver stage antigen-1 (LSA-1), and merozoite surface protein-2 (MSP-2) of Plasmodium falciparum in infants residing in a P. falciparum-hyperendemic area of western Kenya. In this study, development and maintenance of these antibody responses in 28 infants were studied longitudinally by use of monthly serum samples collected from birth to age 1 year. Mother plasma and infant umbilical cord plasma were also tested to assess the transplacental transfer of maternal antibodies. Results showed that antibodies passively transferred from mothers were detectable for CSP, LSA-1, and MSP-2 repeat epitopes. Infants were able to mount and maintain a strong antibody response against LSA-1 in their first year of life. Infants often responded to CSP repeats, but with a much lower antibody titer. Antibody responses in infants against Fc27 and 3D7 repeats of MSP-2 were low throughout their first year. In addition, 51 infants whose first detected infection occurred at > 4 months of age were selected to determine antibody responses to the antigens tested upon their first and second detected infections. Antibody responses to LSA-1 and, to a lesser degree, CSP increased in positivity rates and titer upon second infection. Antibody responses to Fc27-type and 3D7-type repeats of MSP-2 were low upon both infections. There was no association between maternally transferred anti-LSA-1, anti-CSP, or anti-MSP-2 antibodies and an infant's first detected infection. No significant correlation was found between an infant's antibody responses to the 4 antigen repetitive epitopes and protection against malarial parasitemia during the first year of life.

Plasmodium falciparum genotypes, low complexity of infection, and resistance to subsequent malaria in participants in the Asembo Bay Cohort Project

To assess the relationship between the within-host diversity of malaria infections and the susceptibility of the host to subsequent infection, we genotyped 60 children's successive infections from birth through 3 years of life. MSP-1 Block2 genotypes were used to estimate the complexity of infection (COI). Malaria transmission and age were positively associated with the number of K1 and Mad20 alleles detected (COI(KM)) (P < 0.003). Controlling for previous parasitemia, transmission, drug treatment, parasite density, sickle cell, and age, COI(KM) was negatively correlated with resistance to parasitemia of > 500/microl (P < 0.0001). Parasitemias with the RO-genotype were more resistant than those without this genotype (P < 0.0000). The resistance in low COI(KM) infections was not genotype specific. We discuss the impact of genotype-transcending immunity to conserved antigenic determinants. We also propose a diversity-driven immunomodulation hypothesis that may explain the delayed development of natural immunity in the first few years of life and suggest that interventions that decrease the COI(KM) could facilitate the development of protective immunity.

Antimicrobial resistance of bacterial organisms isolated from rats

OBJECTIVE

To determine if antimicrobial resistance occurs in various bacterial species isolated from rats.

METHOD

Two hundred and fifteen rats were trapped from areas in and around Nairobi, Kenya. They were sacrificed and their intestinal, liver and spleen specimens obtained. Various bacterial species were isolated from these specimens. The species were analysed for antimicrobial susceptibility to 12 commonly used antimicrobials using the disc diffusion technique.

RESULTS

The bacterial species isolated included pathogenic and potentially pathogenic ones such as Escherichia coli 137, Salmonella typhimurium 1, Klebsiella pneumoniae 2, Enterobacter cloacae 4, Enterobacter sakazakii 2, Citrobacter freundii 3, Morganella morganii (2), Pseudomonas aeruginosa 2 and Burkhoddria cepacia 6. Depending on the species, the resistance to the various antimicrobials were: 0-100% for cefotaxime, nalidixic acid, cefuroxime, tetracycline, chloramphenicol, co-amoxyclav, sulfamethoxazole, ampicillin, trimethoprim and cephradine, 0-66.6% for gentamicin and 0-25% for apramycin.

CONCLUSION

The results showed that, rats from the study area harboured bacterial species with antimicrobial resistance. These micro-organisms may form an important reservoir for antibiotic resistance which could pose a public health hazard. Control of rat populations, better management of sewer systems and waste dumping sites are recommended in order to reduce occurrence of these drug resistance reservoirs.

Antimicrobial susceptibility and plasmids from Escherichia coli isolated from rats

OBJECTIVES

To determine if antimicrobial resistance occurs in E. coli isolated from rats and if this resistance is transferable via plasmids.

METHODS

Sixty Escherichia coli isolates obtained from 215 rats trapped in and around Nairobi, Kenya, were analysed for antimicrobial susceptibility to eleven commonly used antimicrobials. Plasmid DNA analysis and in-vitro conjugation tests were conducted on twenty two resistant isolates.

RESULTS

A total of 12 (20%) E. coli were resistant to at least one of the commonly used drugs including ampicillin, sulphamethoxazole and streptomycin. Eight (13.3%) isolates were multidrug resistant. The drug resistant E. coli fell into five plasmid profile groups with plasmids ranging between two and 98 megadaltons (Mda). Resistance to ampicillin was transferable.

CONCLUSION

The results of this study show that rats from the study area may form an important reservoir for drug-resistant E. coli that could pose a public health hazard.

Global aspects of antimicrobial-resistant enteric bacteria

Antibiotics have been considered to be safe and effective 'magic bullets', with no disadvantages to their widespread use. This has been proven to be a complacent attitude, with ever-increasing prevalences of resistance now evident. The present review covers aspects of the development, mechanisms and genetics of antimicrobial resistance in enteric commensals and pathogens.

Medical research in Africa: problems and some solutions

This article appeared in the Bulletin of the Royal Society of Tropical Medicine and Hygiene, UK, and is reproduced with kind permission of the authors.

Longitudinal study of natural immune responses to the Plasmodium falciparum apical membrane antigen (AMA-1) in a holoendemic region of malaria in western Kenya: Asembo Bay Cohort Project VIII

We investigated the development and maintenance of proliferative and antibody responses to apical membrane antigen-1 (AMA-1) epitopes in a holoendemic area of western Kenya. Young children (< 10 years), older children (10-17 years), and adults (> or = 18 years) were followed longitudinally for antibody and T-cell responses at 3 time points with an interval of 3-4 months. The proliferative responses against the AMA-1 T epitopes (PL171, PL172, PL173, PL186, PL191, and PL192) were not stable during follow-up; however, response to mycobacterial antigen PPD was highly stable. The responder frequencies were similar in all 3 time points except for epitope PL192. The younger and older children responded more frequently to T-cell epitopes, but the differences were not significant. A positive proliferative response to PL191 was associated with a significantly lower risk of parasitemia at subsequent follow-up (relative risk, 0.5; P = 0.03). The presence of antibody response to B epitopes PL169, PL170, PL173, PL187, and PL192 in one time point was associated with a subsequent response (P = 0.0001-0.008) suggesting a stable response. Younger (P = 0.046) and older children (P = 0.017) more frequently responded to epitope PL169 than did adults, and adults responded more frequently to PL187 than did younger children (P = 0.009). Responses to AMA-1 T-cell epitopes were short lived, and antibody responses were relatively stable.

Molecular characterization of a novel plasmid-encoded cefotaximase (CTX-M-12) found in clinical Klebsiella pneumoniae isolates from Kenya

Nine Klebsiella pneumoniae isolates, six from blood and three from cerebrospinal fluid of newborn babies at Kenyatta National Hospital, Nairobi, Kenya, were analyzed for the mechanism of cephalosporin resistance. By using pulsed-field gel electrophoresis of XbaI-digested chromosomal DNA, all the nine isolates were found to be clonal. PCR and direct sequencing revealed a novel extended-spectrum beta-lactamase, which we designated CTX-M-12. It has a more potent hydrolytic activity against cefotaxime than against ceftazidime and a pI of 9.0 and is encoded on a large self-transferable ca. 160-kbp plasmid.

Fcgamma receptor IIa (CD32) polymorphism is associated with protection of infants against high-density Plasmodium falciparum infection. VII. Asembo Bay Cohort Project

In vitro studies have shown that inhibition of Plasmodium falciparum blood-stage parasite growth by antibody-dependent cellular inhibition is mediated by cooperation between malaria-specific IgG1 and IgG3, but not IgG2, and monocytes via the Fcgamma receptor II (FcgammaRII). A single amino acid substitution at position 131 in FcgammaRIIa is critical in the binding of human IgG subclasses. The hypothesis that the FcgammaRIIa-Arg/Arg131 genotype, which does not bind to IgG2, is a host genetic factor for protection against high-density P. falciparum infection was tested. One hundred eighty-two infants from a large community-based birth cohort study in western Kenya were selected for an unmatched case-control study. Results showed that the infants with the FcgammaRIIa-Arg/Arg131 genotype were significantly less likely to be at risk for high-density falciparum infection, compared with infants with the FcgammaRIIa-His/Arg131 genotype (adjusted odds ratio, 0.278; 95% confidence interval, 0.123-0.627; P=.0021). This finding supports the hypothesis.

Genotypes of multidrug-resistant Salmonella enterica serotype typhimurium from two regions of Kenya

A combination of phage typing and pulsed-field gel electrophoresis of Xbal-digested chromosomal DNA has been used to study the epidemiological relationships of multidrug-resistant Salmonella enterica serotype typhimurium from Nairobi (64 isolates) and Kilifi (40 isolates) collected over the period 1994-1997. Isolates from Nairobi belonged to 11 definitive phage types (DTs) encompassing eight different PFGE patterns. In contrast, isolates from Kilifi were mainly DT 56 (60%) and all fell into a single PFGE pattern. The remaining isolates did not conform to a recognisable phage type. We conclude that multidrug-resistant S. typhimurium infections from Nairobi were caused by multiple strains while those from Kilifi were likely to be from a microepidemic caused by a single clone.

Analysis of plasmid and chromosomal DNA of multidrug-resistant Salmonella enterica serovar typhi from Asia

Molecular analysis of chromosomal DNA from 193 multidrug-resistant (MDR) Salmonella enterica serovar Typhi isolates from 1990 to 1995 from Pakistan, Kuwait, Malaysia, Bangladesh, and India produced a total of five major different pulsed-field gel electrophoresis (PFGE) patterns. Even within a particular country MDR S. enterica serovar Typhi DNA was found to be in different PFGE groups. Similar self-transferable 98-MDa plasmids belonging to either incompatibility group incHI1 or incHI1/FIIA were implicated in the MDR phenotype in S. enterica serovar Typhi isolates from all the locations except Quetta, Pakistan, where the majority were of incFIA. A total of five different PFGE genotypes with six different plasmids, based on incompatibility and restriction endonuclease analysis groups, were found among these MDR S. enterica serovar Typhi isolates.

Antibiotic susceptibility and genotypes of non-typhi Salmonella isolates from children in Kilifi on the Kenya coast

A 4-year retrospective study was undertaken at the Kilifi District Hospital on the coast of Kenya to determine the antibiotic-susceptibility patterns and genotypes of non-typhi Salmonella (NTS) isolates from children. Overall, during the period 1994-97, positive cultures were obtained from 543 (14%) of 3885 blood samples, 364 (30%) of 1210 stool samples and 143 (11%) of 1283 cerebrospinal fluid (CSF) samples. NTS were isolated from 151 (27.8%), 72 (19.8%), and 11 (7.7%) of these positive cultures, respectively. The total 234 NTS isolates were serotyped: the most frequent were Salmonella enterica serotype Enteritidis (41%) and S. enterica serotype Typhimurium (38%). Antibiotic sensitivity testing was done using ampicillin (amp), chloramphenicol (chl), gentamicin (cn), co-trimoxazole (s-t), cefuroxime (cxm), ciprofloxacin (cip), cefotaxime (ctx), amoxicillin-clavulanic acid 20 micrograms-10 micrograms (amc), and tobramycin (tob). Of the 234 isolates, 43 were sensitive to all antibiotics tested and 133 were multiple drug resistant (MDR). The most common resistance type seen was amp, cn, cxm, s-t, ctx, amc, tob (36/234). Our results indicate a high proportion of MDR amongst the isolates from Kilifi. We conclude that 2 major serotypes of salmonella, i.e., S. enterica serotype Typhimurium and S. enterica serotype Enteritidis, of micro-epidemic nature that have been previously unrecognized in Kilifi are responsible for infection in Kilifi district on the coast of Kenya and that over half (56.8%) of total NTS isolates are MDR.

Genotypic analysis of multidrug-resistant Salmonella enterica Serovar typhi, Kenya

We report the emergence in Kenya during 1997-1999 of typhoid fever due to Salmonella enterica serovar Typhi resistant to ampicillin, tetracycline, chloramphenicol, streptomycin, and cotrimoxazole. Genotyping by pulsed-field gel electrophoresis of XbaI-digested chromosomal DNA yielded a single cluster. The multidrug-resistant S. Typhi were related to earlier drug- susceptible isolates but were unrelated to multidrug-resistant isolates from Asia.

Analysis of Salmonella enterica serotype Typhimurium by phage typing, antimicrobial susceptibility and pulsed-field gel electrophoresis

Three typing methods commonly used for bacteria--phage typing, antimicrobial susceptibility and pulsed-field gel electrophoresis (PFGE)- were used to characterise 64 Salmonella enterica serotype Typhimurium isolates from individual adult patients from Nairobi, Kenya. The isolates encompassed 11 definitive phage types (DTs), which fell into eight PFGE clusters; 31.3% of isolates were either untypable or reacted nonspecifically with the phages used for typing and 26.6% were of DT 56. Plasmids of c. 100 kb were responsible for self-transferable multiresistance among the isolates. Analysis by PFGE and phage type demonstrated that multiresistant Typhimurium strains causing diarrhoea and invasive disease were multiclonal.

Typing of Salmonella enterica serotype paratyphi C isolates from various countries by plasmid profiles and pulsed-field gel electrophoresis

Pulsed-field gel electrophoresis (PFGE) of 61 Salmonella enterica serotype Paratyphi C isolates from six countries gave five distinct clusters. Twenty-four isolates from five countries were susceptible to 10 antimicrobials tested and gave similar restriction endonuclease digest patterns of the 38-MDa plasmid. In contrast, plasmid and PFGE profiles of 37 multidrug-resistant isolates from Zaire were different from those from other countries.

Genotype analysis of Escherichia coli strains isolated from children and chickens living in close contact

Escherichia coli isolates from rectal swabs from 62 chickens and stools from 42 children living in close contact with chickens on the same farms in Kiambu district, Kenya, were compared for their genetic relatedness. Antibiotic susceptibility profiles broadly categorized isolates from the children and from the chickens into two separate clusters: the majority (144; 85.5%) of the E. coli isolates from children were multidrug resistant, while the majority (216; 87.1%) of the E. coli isolates from chickens were either fully susceptible or resistant only to tetracycline. Sixty- and 100- to 110-MDA plasmids were found to encode the transferable resistance to co-trimoxazole and tetracycline. HindIII restriction endonuclease digestion of the 60- and 100- to 110-MDA plasmids produced four distinct patterns for isolates from children and three distinct patterns for isolates from chickens. XbaI digestion of genomic DNA followed by pulsed-field gel electrophoresis (PFGE) analysis produced 14 distinct clusters. There were six distinct PFGE clusters among the isolates from children, while among the isolates from chickens there were seven distinct clusters. Only one PFGE cluster contained isolates from both children and chickens, with the isolates displaying an approximately 60% coefficient of similarity. This study showed that although several different genotypes of E. coli were isolated from children and chickens from the same farms, the E. coli strains from these two sources were distinct.

Characterization of antibiotic resistance plasmids from Bordetella bronchiseptica

Of 52 antibiotic-resistant Bordetella bronchiseptica isolates from cats, ten carried plasmids. Only two of these plasmids, pLV1400 and pLV1401, were self-transmissible to Escherichia coli K12; both plasmids encoded resistance to ampicillin, tetracycline, sulphonamides, streptomycin and mercuric chloride, and were of incompatibility group P (IncP). Transferable tetracycline resistance has not been reported in B. bronchiseptica previously. The plasmids were identical in size (c.51 kb), restriction endonuclease digestion pattern and gene sequences (trfA and korA) within the IncP replicon. The trfA and korA sequences differed from those of the archetypal IncP plasmids RP4 and R751. Although the two B. bronchiseptica isolates were from epidemiologically and geographically separated cats, pulsed-field gel electrophoresis of their XbaI- or DraI-digested chromosomal DNA indicated that they were genotypically identical. The plasmid-encoded ampicillin resistance was mediated by a penicillinase of molecular weight 49,000, and pI 8.45 which was inhibited by clavulanate (IC50 = 0.1 mg/L) and tazobactam (IC50 = 0.42 mg/L) but not by parachloromercuribenzoate or EDTA. The high-level tetracycline resistance was mediated by a class C efflux mechanism that has not been described previously in this genus. The presence of transferable multi-drug resistance on a promiscuous plasmid may limit options for therapy of respiratory tract infection in companion and farm animals.

Plasmid diversity of multi-drug-resistant Escherichia coli isolated from children with diarrhoea in a poultry-farming area in Kenya

Biotin-labelled DNA probes and restriction-endonuclease digestion (RED) with HindIII were used to study the diversity of resistance plasmids (R-plasmids) from 414 Escherichia coli isolates: 168 from children living in close contact with antibiotic-fed poultry and 246 from the chickens. Full sensitivity to all 10 antimicrobials tested was more common in the isolates from poultry than in those from the children (36.2% v. 9.5%; P < 0.001). Multi-drug resistance, to at least two of the antimicrobials, was relatively common in the isolates from the children (85.5% v. 26.00%; P < 0.001). Overall, 31% of the poultry isolates were resistant to tetracycline alone. Resistance to amoxycillin was due to production of TEM-1 (89%) and TEM-2 (11%). In > 71% of the isolates from children and 79% of those from poultry, resistance was encoded on a 100-110-kb transferable plasmid belonging to incompatibility group FII. However, RED patterns of R-plasmids from the two groups of isolates were highly diverse and not indicative of any close relatedness. This difference in patterns and in the levels of multi-drug resistance indicate that the isolates from the children and those from the poultry represent two distinct pools of resistance plasmids.

Molecular typing of multi-drug resistant Shigella dysenteriae type 1 by plasmid analysis and pulsed-field gel electrophoresis

Recently, an outbreak of dysentery due to multi-drug resistant Shigella dysenteriae type 1 strains was reported along the coastal area of Kenya and shortly thereafter another outbreak appeared in the outskirts of Nairobi. We analysed 22 multi-drug resistant S. Dysenteriae type 1 strains isolated from cases in the latter outbreak using plasmid deoxyribonucleic acid (DNA) profiles and pulse-field gel electrophoresis of genomic DNA. All isolates were resistant to commonly available drugs including ampicillin, trimethoprim, sulphamethoxazole, chloramphenicol, tetracycline and streptomycin with minimum inhibitory concentrations > 64 micrograms/mL, but were fully sensitive to gentamicin. Only 2 strains were resistant to nalidixic acid. Analysis of plasmid DNA and genomic DNA revealed that all 22 strains were clonally related. It is likely that the present outbreak was related to that on the coast, as suggested by the similarity in drug susceptibility data. The drug susceptibility and molecular epidemiological data provide a useful baseline for future monitoring of epidemic and endemic S. dysenteriae activity in East Africa.