The focus of the global diarrhoeal disease burden is in low and middle-income countries, where the disease epidemiology and aetiology is highly variable and not well characterised. The aim of this thesis was to challenge the knowledge gaps regard ing diarrhoeal disease in children under the age of five in Ho Chi Minh City (HCMC), Vietnam. Firstly, a pilot surveillance in southern Vietnam demonstrated a preponderance of enteric viruses in hospitalised diarrhoeal children and reported the first rotav irus GI2 in Vietnam; despite being geographically disproportional distributed, rotav irus (RoV) predom inated fo llowed by norovirus (NoV). On the basis of these data, a prospective multi-centre hospita lbased surveil!ance was conducted in HeMe to study diarrhoeal disease in detail and \ investigate the extent and the ep idemiology of the hypothes ized NoV emergence. Faecal , specimens from diarrhoea patients and diarrhoea-free chi ldren were screened for a panel of pathogens; RoV was again identified as the predominant agent, fo llowed by NoV. Enteric bacteria were found at smaller proportions, and exhibited excessive antim icrobial res istance. As NoV was found to be highly endemic and a major cause of hospita lisation, a risk factor analysis for NoV infections was performed. Ri sk facto rs in cluded young age, residential crowding and contact with symptomatic individ uals. Additional analys is on the phylogenetic structure of NoV stra ins demonstrated diverse genotypes circulating, most commonly belonging to the GIIA lineage. A spatioremporal analysis of 0 11.4 variants, GI1.4-2006b (Minerva) and the novel emergent GIL4-20 10 (New Orleans), suggested a strain replacement phenomenon and detected a cluster of 0 11.4-201 0 in the northeastern part of the city. These studies indicate prominent di sease dynam ics involved rapid evolution of vi ruses, necessitate studies on strain distribution and genomic analyses and potenti al source additi onally f contributing to genetic variations (animal reservoirs), and suggest considerable impact of RoV and NoV immunisation in Vietnam.

Two studies were performed to detect aetiology of acute diarrhoea in hospitalized children aged under five years in Tripoli, Libya. In the first study, two hundred and thirty-six stool samples were obtained. Of these, 118 were from patients admitted for acute diarrhoeal disease, and 118 age and sex-matched concurrent controls were admitted for other reasons. In the second study, eight hundred and ten stool specimens were collected 405 from patients and the same number from controls. All were admitted to the AIjala Children’s Hospital, Tripoli, Libya. The first study was conducted between August 1st 1997 and 31st October 1997 and the second study was conducted between January 1st 2003 and 31st December 2003. One or more enteric pathogens were isolated from 55.9% of patients and 13.6% of controls in the first study and 68.1 % of patients and 12.6% of controls in the second study. In the first study, the organisms were identified from stool of patients; Escherichia coli 22.9%, rotavirus 15.3%, Campylobacter 7.6%, Proteus 7.6%, Klebsiella 4.2%, Entamoeba histolytica 4.2%, Cryptosporidium 2.5% and Giardia lamblia 1.7%, Salmonella was not isolated in both studies, because not growth on ordinary media were used (MacConkey agar and Blood agar) but usually growth on Salmonella-Shigella medium where not used. In the second study, enteropathogens identified were: rotavirus 30.4%, Escherichia coli 16.5%, Entamoeba histolytica 12.5%, Campylobacter 6.7%, Giardia lamblia 3.7%, Cryptosporidium 3.2%, Klebsiella 2.9%, Proteus 2.2%. Libyan children under six months of age were the most susceptible to acute diarrhoea requiring admission to the hospital. This was remarked in 46.6% of patients in the first study and 43.2% in the second. Exclusive breast feeding in Libyan children was of a very low percentage. In the first study it was 19.5% and in the second 29.1%. Children use dummies were about 3 times more at risk of diarrhoea than the non users in the first study (OD: 5.95,95%, CI: 1.120-2.37, p<0.001) and RR: 3.1 and (0: : 2.986ý 95%. Cl: 2.13-4.16, P<0.001) and RR: 23 in the second, this fell to children being twice as much at risk of contracting diarrhoea. Watery stool was the most common stool consistency of patients in both studies. Fever was the most common clinical feature associated with acute diarrhoea in the two studies (72.9% and 71.6% respectively). Vomiting was present in 51.7% of patients among the first study and 58.3% among the second. Moderate and isotonic dehydration were the most common degree and type of dehydration across both studies. In the second study, Rotavirus peaked during the winter (cold season) while bacteria and parasites peaked during the summer and autumn seasons. API 20E and API Campy were used to identify bacterial isolated by cultures and the number of confirmed cases decreased from 142 to 112 samples. Polymerase Chain Reaction was adopted in the second study to confirm detection of Campylobacter spp. these were identified by API Campy technique, where all Campylobacter spp. were identified as the same as detected by API Campy and for 24 samples.