Current epidemiological status of enterohaemorrhagic Escherichia coli O157:H7 in Africa

Abstract

Enterohaemorrhagic E. coli (EHEC) has been isolated from human diarrhoeal disease, hemorrhagic colitis (HC), and haemolytic uremic syndrome (HUS). After 20 years since the first description of E. coli O157: H7 in USA, EHEC has become an important public health problem worldwide.1,2 Given the magnitude and severity of recent outbreaks of E. coli O157: H7 infection, there is an urgent need to reduce the human hazard caused by this pathogen. Cattle are considered as major reservoir of E. coli O157:H7 because consumption of undercooked meat products from cattle has been often associated with many human infections. EHEC strains belonging to serogroup EHEC O157 are most frequently associated with human disease. They have the flagellar (H7) antigen or are nonmotile (H-).3 However, EHEC strains of other serotypes from human, animal and food sources have been reported.3 EHEC strains produce one or two principal shiga toxins (ST1 and ST2). ST1 is almost identical to shiga toxin produced by Shigella dysenteriae type 1, whereas ST2 is antigenically distinct.4 Strains of O157 EHEC isolated in Britain commonly produce ST2 only. Strains elaborating both toxins are found less frequently, and ST1 producers are relatively rare.5 Morphologically, E.coli O157:H7 is indistinguishable from other E.coli serotypes. Culturally E. coli O157:H7 distinctly do not ferment sorbitol and gulucuronide after 24 hours of incubation.3 GEOGRAPHICAL DISTRIBUTION OF EHEC O157 EHEC O157:H7 has emerged globally as an important food-borne pathogen. The number of infections caused by EHEC has increased significantly since the first reported outbreak in the US in 1982.1E. coli O157:H7 infections have been reported most frequently in developed countries, although illness due to E.coli O157:H7 have been reported in over 30 countries on six continents.2,3,6–9 Morbidity and mortality associated with O157:H7 and the threat to public health of infections with EHEC O157 and other EHEC in particular, led the Public Health Laboratories Services (PHLS) to develop interim guidelines for control that were published in 1995.10 Although reported outbreaks of E.coli O157 in Africa have been few to date, available information indicates that the pathogen has wide geographic distribution. Since the outbreak in 1992, cultureproven E.coli O157 diarrhoeal illness has been reported from multiple locations, in South Africa by Browning et al,11 Swaziland,12 and in Central African Republic,13 and Kenya,14 Gabon,15 Nigeria,16 and Ivory Coast.17 A few features were common in all these outbreaks that most of them occurred in small or remote areas, and there were concomitant or preceding outbreaks of diarrhoeal disease due to other enteric pathogens that could have masked the outbreak.18–20 The transmissions have been food or water borne, but person-to-person has contributed to the severity of the outbreaks.20 The major problem with E.coli O157 is that is not detected by the usual methods used to isolate and identify “traditional” enteric bacterial pathogens. Also, microbiology laboratories in many countries of Africa do not routinely test E.coli O157:H7, hence many infectionsmay go unrecognized.21,22 Reports on African dysentery outbreaks attributed to Shigella spp sometimes indicate that specimens were not tested for EHEC until several months into the outbreak or do not describe laboratory methods that are suitable for detecting E.coli O157:H7.23,24 This is unfortunate because the spectrum of clinical illness resulting from Shigella spp infection overlaps considerably with that of E.coli O157 and mixed outbreaks have been reported.18 Diagnosis of shigellosis is made clinically by the typical features of bacillary dysentery with blood and mucus in stool although some cases may present with mild to moderate watery diarrhea while the EHEC diarrhea is usually bloody without mucus. Confirmation is made by stool culture, serological and biochemical tests. Important public health measures include educating the public on the danger of eating undercooked meat, increasing awareness among clinicians of E.coli O157:H7 infection and mandating case reporting will go a long way to control infections associated with E. coli O157:H7 in Africa. REPORTS OF ENTEROHAEMORRHAGICE.coliO157:H7 FROM AFRICA COUNTRIES South Africa The first reported case of EHEC in the world was in 1982 in USA.1 In South Africa, the first reported E. coli O157:H7 hemorrhagic colitis case was in 1990 by Browning et al.11 Since then, many sporadic cases of bloody diarrhoea have been reported in many areas of South Africa. Effer et al19 reported EHEC from South Africa in 1992, and a large outbreak of bloody diarrhoea caused by E.coli O15:H7 infections occurred in Swaziland, Southern Africa. A total of 40912 patients of less than five years of age visited physicians for diarrhoeal problems from October through November, 1992. This was a seven-fold increase over the same period during 1990 — 1991. The infection rate was 42% among 778 residents screened. Female gender and consumption of beef and untreated water were significant contributing factors for illness. E.coli O157:NM (non-motile) was recovered from seven affected foci in Swaziland and South Africa in 1992, 27 of 31 patients, and environmental isolates had undistinguishable pulsed field gel electrophoresis patterns. Compared with previous years, a five-fold increase in cattle deaths occurred in October 1992 due to drought. The first heavy rains fell in the same month (36 mm), following 3 months of drought. The marked increase in cattle deaths indicated that available pastures and water sources were often inadequate. Drought, carriage of E.coli O157:H7 by cattle, and heavy rains with contamination of surface water appears to be important factors contributing to EHEC outbreak.19 Molecular techniques were also used to study the epidemiology of diarrhoeal infections due to E.coli in Gouteng region in South Africa. A total of 151 E.coli isolates from patients with diarrhoea and 30 strains isolated from healthy individuals were collected between March 1996 to May 1997, an isolation rate of 7.7% of enterohaemorrhagic producing E.coli O157:H7 serotype was reported.25 Muller et al26 also investigated the occurrence of E.coli O157:H7 in selected water samples in South Africa using chromogenic Rainbow agar O157 medium. A total of 204 samples were selected from 15 different sites, where water was used for human consumption. In their study none of the suspected colonies contained all the virulence factors necessary to classify them as E.coli O157:H7. For example none of these organisms agglutinated with antisera to E.coli O157:H7. They concluded that the probability of being infected with E.coli O157:H7 from consumption of the river water sources was low. Some samples did, however, contain enterohaemorrhagic E.coli virulence properties, such as Shiga toxin 1 and 2 (Stx1 and Stx2), and enterohaemolysin, which might impose a health risk if ingested. In another study conducted by the same author using immunomagnetic separation (IMS) method in combination with the E.coli O157:H7 selective media, immunoassays, biochemical tests and PCR, to assess the prevalence of E.coli O157:H7 in selected sewage and environmental water in South Africa, a total of 91 sewages and 40 river water samples were tested. Of these 17.6% and 20% yielded suspected E.coli O157:H7 colonies on CTSMAC agar medium respectively. PCR was used to confirm the presence of genes coding for Stx1, Stx2, enterocyte attaching and effacing genes (eae) and enterohaemolysin (ehly). Three colonies from one sewage sample (1.1%) agglutinated with anti-E.coli O157 and H7 antiserum, and contained the genes coding for Stx 2, eae, and ehly. None of the colonies isolated from the river water samples were positive for E.coli O157:H7. Evidence has been presented that the enrichment-IMS-selective agar procedure substantially increased the sensitivity of E.coli O157:H7 isolation compared to direct plating of test samples onto selective agar.27 East Africa In Uganda, faecal samples were collected from 237 diarrhoeic infants in Kampala, and 59 healthy cattle from a ranch in the Central Region of Uganda were investigated for the presence of E.coli O157:H7 and other types of enterohaemorrhagic producing E.coli (EHEC) by Kaddu-Mulindw et al,28E.coli O157:H7 was not detected in 150 stool samples on Sorbitol MacConkey agar (SMAC). A total of 87 additional human stool samples tested with an enzymeimmunoassay for enterohaemorrhagic toxins (Premier EHEC) were also negative. In the same study by Kaddu-Mulindw et al,28 EHEC were isolated from 45 of 159 cattle from a herd in the Central Region of Uganda. EHEC strains from cattle belonged to different O and 9 different H types and nine O:H types were identical to those found in bovine EHEC from other continents. One bovine EHEC strain was positive for the eae gene, and O groups associated with enterohaemorrhagic E.coli (EHEC) types (O26, O103, O111, O145, and O157) were not found. Their reports demonstrated that EHEC were not frequent in urban children in Uganda, but domestic cattle were identified as an important natural reservoir for these organisms in Uganda. In Kenya, Arimis et al29 reported E. coli O157:H7 serotype in two samples (<1%) of milk collected in Nairobi. One of the two isolates produced verocytoxins. In Tanzania, Gaswn et al30 conducted a study by matched case-control study in the Maternal and Child Health Clinic (MCH) in Ifaraka during the rainy season in order to elucidate the risk factors for and etiology of diarrhoeal diseases in children under 5 years of age. Enterohaemorrhagic, enteropathogenic, enterotoxigenic and entroaggregative strains of E.coli were not related with diarrhoea and neither were Giardia lamblia or Salmonella species. But studies on beef by Hayghaimo et al31 here have shown that carcasses were contaminated with EHEC organisms. The authors concluded that this might pose a health hazard following consumption of under cooked of meat and meat products in this region. West Africa In Nigeria, Akinyemi et al32 studied E. coli infections for a period of over 12 months. A total of 852 stool samples from patients (both children and adults) with acute diarrhoeal diseases attending public and recognized health delivery institutions in Lagos metropolis, were screened for diarrhoeagenic bacterial agents. Of all 83 isolates of E.coli found, seven (8.4%) were EHEC. Their study further emphasize on the important role of EHEC in acute gastroenteritis in children in Lagos, Nigeria. In another study by Ogunsanya et al,33 it was reported a 3% prevalence of EHEC from children under 5 years old with diarrhoea (n=215) and without diarrhoea (n=100) seen at paediatric clinics investigated for bacteria, viral and parasitic enteropathogens in Lagos. Okeke et al34 carried out a study in small-town and rural primary health care centers in South-western Nigeria. A total of 330 E. coli strains isolated from 180 children with diarrhoea and from 144 apparently healthy controls were examined for virulence traits. Using the colony blot hybridization, the results showed that 1.2% of the strains were enterohaemorrhagic E.coli. The E.coli strains that hybridized with a shiga toxin gene probe that lacked other characteristics usually present in enterohaemorrhagic E.coli constituted 8.4%. Olorunshola et al16 examined the prevalence of sorbitol-nonfermenting E.coli O157:H7 (EHEC) in 100 patients with diarrhoea by stool culture on sorbitol macconkey agar in Lagos Nigeria. The detection rate of O157:H7 was 6%. Five of the six patients were children below 5 years of age and one was a teenager. All strains induced cytotoxic effect in the vero-cell assay, and were susceptible to most of the antimicrobial agents tested. Olorunshola et al16 recommended that there should be adequate meat and food inspection to improve the general hygiene of local fast food restaurants; so-called “bukkas”, which are regarded as likely sources of infection. Recently, Smith et al35 reported 17% EHEC O157:H7 from healthy animals in Lagos Nigeria. The plasmid profiles of the isolates revealed that 47% harboured detectable plasmids ranging in size from 0.564 kb to >23 kb. However, Okeke et al20 reported that there was no isolates of EHEC O157:H7 from patients with diarrhoea in the southwestern part of Nigeria. In Cote d'Ivoire (Ivory Coast) the first reported enterohemorrhagic producing E.coli was from Dadie et al17 who reported two O157:H7 strains from children. One O157:H7 was isolated from children and the other O157:NM (non-motile) from human diarrhoea stool specimens. Both O157 strains carried Stx 2, eae, and glucouronidase gene (Uid A), but not enterohaemolysin gene (ehly). The authors concluded that E.coli did not appear to be a public health problem in Cote d’ Ivoire. In Gabon, Presterl et al15 reported that EHEC were not associated with children diarrhoea in this region either. Central Africa Germanii et al13 first reported EHEC in the Central African Republic in a small village of Zémio, located on the Democratic Republic of Congo border. Outbreaks of bloody diarrhea in 1996 were attributed to E.coli O157 from molecular test results. Since 2001, an increasing number of cases of acute bloody diarrhea have been reported in Kinshasa usually between the months of June and August. During the 2003 outbreak, an investigation could not be conducted; possible routes of transmission would include person-to-person contact, related to lack of hygiene, and contaminated food and water. In Cameroon, the first reported E.coli O157:H7 case was in November 1997 and April 1998 when bloody diarrhoea of 298 sick people was investigated in a laboratory.13,36 It was reported that the fatality rate was 16.4% and amoebiasis was documented in one of the three patients. Three types of pathogens were also found. The pathogens were multiple drugs resistant S. dysenteriae type 1, S. boydii and enterohaemorrhagic E.coli O157:H7. In the Central African Republic (especially in 1998) the major contributing factors of the E.coli O157 outbreak were consumption of smoked zebu meat and contaminated drinking water.36 Studies of E.coli O157 carriage rates among livestock, food, and environment in this central African area might be useful in assessing the potential for future outbreaks. Recent reported outbreak in this region by Koyange et al37 indicated that during the rainy season (from April to September 2003), 463 children ≤15 years of age (median 10 months) with severe diarrhea were admitted to the Pediatric Hospital of Kalembelembe in Kinshasa, Democratic Republic of Congo (DRC). The population of the outbreak area was approximately one million. Children with bloody diarrhea but without fever were treated. They came from six districts of Kinshasa (Bumbu, Selembao, Makala, Kimbanseke, Masina, and Ndjili). Abdominal cramps, nausea, vomiting, and dehydration were uncommon. The duration of illness ranged from 5 days to 2 weeks. Available antimicrobial drugs, trimethoprim-sulfamethoxazole, and ampicillin showed no effect against the illness. Fifty-six infants died between June and July with symptoms of H US. H US occurs in approximately 8% of children and an unknown proportion of adults infected with E.coli O157 and cases can be fatal if no hemodialysis is performed. The high death rate of infants during this outbreak was linked to the lack of treatment (mainly hemodialysis) at the beginning of the epidemic. More investigations are needed to better define the incidence and epidemiology of E.coli-associated diarrhea in the DRC so that optimal recommendations for preventing and managing illness can be developed. North Africa The only report available was that of a survey done in middle Egypt to determine if E.coli O157:H7 was present in 175 samples of raw ground beef, chicken, lamb and unpasteurized milk. The pathogen was detected in 6% of the beef samples, 4% chicken samples, 4% lamb samples and 6% milk samples obtained from slaughter houses, supermarkets and farmers homes.38 CONCLUSIONS Surveillance of EHEC O157:H7 infection is well established in many developed countries and it is apparent that there are geographical differences in the incidences of infection. Although cattle and other ruminants are regarded as the main reservoirs of EHEC, these bacteria have also been isolated from water, milk and a number of non-ruminant animal species. Substantial gaps in knowledge about epidemiology of EHEC in developing countries exist. Public health awareness about the problem is needed, as are strengthened diagnostic facilities for EHEC. The goal shall be towards setting up national surveillance programs. Such programs would determine the incidence rates, epidemiological risk factors, interaction of HIV/AIDS and EHEC, seasonal variation, current state of resistance to antimicrobial agents, role of serotypes other than O157. Collaboration among researchers in developed and developing countries need to be strengthened, leading to the development of regional centres of excellence. This approach should contribute to understanding of the global epidemiology of human enterohaemorrhagic E. coli O157:H7.