The prevalence and the incidence are two primary epidemiological parameters in infectious disease modelling. The incidence is also closely related to the force of infection or the hazard of infection in survival analysis terms. The two measures carry the same information about a disease because they measure the rate at which new infections occur. The disease prevalence gives the proportion of infected individuals in the population at a given time, while the incidence is the rate of new infections. The thesis discusses methods for estimating HIV prevalence, incidence rates and the force of infection, against age and time, using cross-sectional seroprevalence data for pregnant women attending antenatal clinics. The data was collected on women aged 12 to 47 in rural KwaZulu-Natal for each of the years 2001 to 2006. The generalized linear model for binomial response is used extensively. First the logistic regression model is used to estimate annual HIV prevalence by age. It was found that the estimated prevalence for each year increases with age, to peaks of between 36% and 57% in the mid to late twenties, before declining steadily toward the forties. Fitted prevalence for 2001 is lower than for the other years across all ages. Several models for estimating the force of infection are discussed and applied. The fitted force of infection rises with age to a peak of 0.074 at age 15, and then decreases toward higher ages. The force of infection measures the potential risk of infection per individual per unit time. A proportional hazards model of the age to infection is applied to the data, and shows that additional variables such as partner’s age and the number of previous pregnancies do have a significant effect on the infection hazard. Studies for estimating incidence from multiple prevalence surveys are reviewed. The relative inclusion rate (RIR), accounting for the fact that the probability of inclusion in a prevalence sample depends on the individual’s HIV status, and its role in incidence estimation is discussed as a possible future approach of extending the current work. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

This study was carried out to investigate different aspects of the epidemiology of the common intestinal protozoan infections in children in KwaZulu-Natal. The main aspects studied were to: i . monitor changes in the prevalence and intensity of the common intestinal protozoons in children after receiving antihelmintic drugs, ii. determine whether environmental and/or socio-economic factors are important in the prevalence of the common intestinal protozoons, iii. determine the occurrence of Cryptosporidium parvum in stool samples of paediatric patients with gastroenteritis and in healthy school children. Intestinal protowan species often co-occur with intestinal nematodes in infected children and it is important to determine the effect that anti-nematode treatment has on concomitant protozoan infections. The study included the analysis of stool samples by the Formol-Ether Concentration Technique, exam ination of the obtained sediments for intestinal helminths and protozoan species, and treatment of nematode-infected individuals. Four surveys were carried out to determine the prevalence and intensity of intestinal protozoons in school children before and after anthelmintic chemotherapy, and the X(2) test was used to determine significant changes. Prevalences and intensities of helminths were determined for significant changes after treatment using the Student's t-test. Additional pre- and post-treatment prevalence data were obtained from four schools in Health Region A of KwaZulu-Natal. The prevalence of Ascaris lumbricoides decreased significantly from 75.2% to 9.7% after the first treatment, that of Trichuris trichiura decreased from 77.7% to 62. 1%, and hookworm infections (presumably Necator americanus) dropped fromI2.7% to 1.0% and remained very low for the rest of the study. Very few individuals were infected with protozoan species and for statistical analysis, these were combined. The prevalence of protozoan infections increased from 33.0% to 50.3% after the first treatment and from 35% to 42% after the second treatment. The prevalence of A. lumbricoides decreased significantly again after the second treatment while there was no significant decrease in the prevalence of T. trichiura. The intensities (number of eggs/gram of feaces) of the three nematodes also decreased significantly after the two treatments. It is recommended that children who have been treated for nematode infections should also be examined for protozoan infections, and these should also be treated accordingly. A retrospective analysis of protozoon prevalence data from different surveys in KwaZulu-Natal was done in order to detennine the importance of environmental and/or socio-economic factors in the distribution of intestinal protozoons. These data were plotted on the map of KwaZulu-Natal using Geographic Information System (GIS). Univariate analysis was carried out to determine significant correlations between the prevalences of protozoan species and selected variables. The significant correlations obtained were moderate and no strong correlations were obtained. Univariate stepwise regression analysis was performed to determine the factors that combine best in facilitating the transmission of protozoan species and significant associations were obtained between the prevalence of protozoon species and a combination of environmental and socio-economic factors. In most cases, the association between prevalence and mid-summer temperature and rainfall were the most significant. This is an indication of increased summer transmission. Altitude was significantly correlated only with the prevalence of Endolimax nana. The fact that moderate correlations were obtained between prevalence of intestinal protozoons and climatic and socio-economic factors indicates that these factors are important in the distribution of the common intestinal protozoons. However, lack of strong correlations suggests that in addition to climatic and socio-economic factors, there are other factors that have an effect on the distribution of intestinal protozoan species. In the multivariate analysis where the variables were simultaneously considered, the presence of electricity was the only factor that was significantly associated with the variation seen in the prevalence of intestinal protozoons in the different study locations. Cryplosporidium parvum is a parasitic protozoon that is associated with severe fatal diarrhoea in children and immunocompromised individuals. Oocysts of this parasite were found in 18.2% of stool samples collected from children (aged 6 to 48 months) who were admitted in the paediatric wards at King Edward VIII Hospital, Durban. The stool samples were firstly concentrated using the Formal-ether method and the obtained sediment was mixed with the Sheather's Sucrose solution and examined microscopically. No oocysts were found in stool samples collected from older primary school children. Although the diarrhoea in these children might have also been due to other causes, the results obtained further show the importance of C. parvum as a cause of diarrhoea in children below the age of five years. Knowledge of the epidemiology of C. parvum is crucial in the control of this parasite as there is currently no effective treatment. More intensive surveys are needed in detennining the epidemiology of this pathogen in the South African population. / Thesis (M.Sc.)-University of Natal, Durban, 2001.

Introduction Willingness to participate in clinical trials is a crucial element in recruitment of suitable participants for intervention trials. Measurement of willingness to participate assists in determining community preparedness for clinical trials, such as HIV vaccine trials. Therefore, researchers have developed a Clinical Research Involvement Scale (CRIS) to assess willingness to participate modelled on the Theory of Reasoned Action. The CRIS was tested in the USA and was noted that it would benefit from additional testing in other populations. Aim The purpose of this study is to determine whether racial differences exist in willingness to participate and explore potential factors associated with willingness to participate in HIV prevention research. Methods A cross sectional analytic study was conducted. The CRIS was administered to university students aged 18-45 at the University of KwaZulu-Natal in South Africa. The CRIS was administered online with a demographic questionnaire to facilitate evaluation of possible associations between willingness to participate and age, gender, relationship status, parity, religion, education status, student status, employment status and access to private health care. Participation was once-off at the time of completing the scale. Results The study enrolled 636 participants, two thirds being female. An effective sample size of 509 was considered for analysis after data was cleaned for accuracy and completeness. The results indicated that all students across all race groups were willing to participate in HIV prevention research. However, when considering factors that affected willingness to participate, statistically significant differences were noted. Based on the differences amongst these factors, Black students expressed greater intention to participate compared to White and Indian students. The CRIS was deemed a reliable instrument in this population; however in its current structure it did not show strong validity. Validity improved if the factors of motivation to comply and outcome evaluations were removed in this population. Discussion The study findings are specific to students of the University of KwaZulu-Natal and cannot be generalized to other populations. The racial differences in factors that affect willingness to participate indicate differences in risk perception and seeking access to better quality healthcare. Recommendations The CRIS should be used in other student populations to assess its validity. (350 words) / Thesis (M.Med.Sc.)-University of KwaZulu-Natal, Durban, 2013.