We compared the relative risks of mother-to-child transmission of Toxoplasma gondii and clinical manifestations due to congenital toxoplasmosis associated with intensive prenatal treatment in Lyon and Austria, short term treatment in 51% of Dutch women, and no treatment in Danish women. For each cohort, relative risks were standardized for gestation at seroconversion. In total, 856 mother–child pairs were studied: 549 in Lyon, 133 in Austria, 123 in Denmark and 51 in The Netherlands. The relative risk for mother-to-child transmission compared to Lyon was 1·24 (95% CI: 0·88, 1·59) in Austria; 0·59 (0·41, 0·81) in Denmark; and 0·65 (0·37, 1·01) in The Netherlands. Relative risks for clinical manifestations compared with Lyon (adjusted for follow-up to age 3 years) were: Austria 0·19 (0·04, 0·51); Denmark 0·60 (0·13, 1·08); and The Netherlands 1·46 (0·51, 2·72). There was no clear evidence that the risk of transmission or of clinical manifestations was lowest in centres with the most intensive prenatal treatment.

The aim of the study was to elucidate the epidemiological features of Hepatitis C virus (HCV) infection among teenagers in an endemic area by conducting a mass screening study. We also investigated the clinical outcome of the anti-HCV-positive subjects by conducting subsequent short-term and long-term follow-up studies. All 2837 students of two junior middle schools in Tzukuan, aged 13–16 years, were invited to be screened for anti-HCV, HBsAg, AST and ALT in October 1995. A total of 2726 (96%) students responded. Anti-HCV, HCV RNA and aminotransferase levels were evaluated among anti-HCV-positive students 1 month and 30 months later, respectively. A total of 38 (1·4%; M/F = 22/16) participants were anti-HCV-positive. The anti-HCV-positive students had higher rates of exposures to transfusion, anti-HCV-positive families and surgery. The prevalence (2·8%) of the 7 maritime villages was markedly higher than that (0·7%) of the other 8 villages (P < 0·001). Subsequent follow-up studies demonstrated that there might be 5 cases of acute or recent HCV infection, and 6 cases who had recovered from chronic HCV infection.

To estimate the burden of disease due to congenital toxoplasmosis in Sweden the incidence of primary infections during pregnancy and birth prevalence of congenital toxoplasmosis in 40978 children born in two regions in Sweden was determined. Women possibly infected during pregnancy were identified based on: 1, detection of specific IgG based on neonatal screening of the phenylketonuria (PKU) card blood spot followed by retrospective testing of stored prenatal samples to detect women who acquired infection during pregnancy and follow up of their children to 12 months; 2, detection of specific IgM on the PKU blood spot.

The birth prevalence of congenital toxoplasmosis was 0·73/10000 (95% CI 0·15–2·14) (3/40978).

The incidence of primary infection during pregnancy was 5·1/10000 (95% CI 2·6–8·9) susceptible pregnant women. The seroprevalence in the southern part was 25·7% and in the Stockholm area 14·0%.

The incidence of infection during pregnancy was low, as the birth prevalence of congenital toxoplasmosis. Neonatal screening warrants consideration in view of the low cost and feasibility.

In order to establish the differences in transmission pattern of varicella-zoster virus (VZV), a comparative seroepidemiological study was carried out in two different children samples. Children aged 1–11 years, were randomly selected from state schools of São Paulo city, Brazil. Individuals aged 1–15 years were sampled by cluster from Caieiras city. Children aged 3 years or under from Caieiras were not attending school, while those from São Paulo were attending all-day nurseries or kindergarten. The presence of antibodies to VZV was analysed by ELISA technique. The force of infection and contact rate were determined by mathematical techniques. The average age of first infection was 2·87±0·14 years and 4·07±0·47 years for São Paulo and Caieiras, respectively. The average force of infection estimated was 0·29 year−1 for São Paulo and was 0·26 year−1 for Caieiras. The proportion of seropositivity and the force of infection were higher in São Paulo school children up to 3 years of age compared with Caieiras children, where the social contact starts later. In conclusion, social changes affecting contact among children may influence varicella epidemiology.

Many countries are currently studying the possibility of mass vaccination against varicella. The objective of this study was to provide a comprehensive picture of the pre-vaccine epidemiology of the varicella zoster virus (VZV) to aid in the design of immunization programs and to adequately measure the impact of vaccination. Population-based data including physician visit claims, sentinel surveillance and hospitalization data from Canada and the United Kingdom were analysed. The key epidemiological characteristics of varicella and zoster (age specific consultation rates, seasonality, force of infection, hospitalization rates and inpatient days) were compared. Results show that the overall epidemiology of varicella and zoster is remarkably similar between the two countries. The major difference being that, contrary to Canada, the epidemiology of varicella seems to be changing in the United Kingdom with an important decrease in the average age at infection that coincides with a significant increase in children attending preschool. Furthermore, differences exist in the seasonality between the United Kingdom and Canada, which seem to be primarily due to the school calendar. These results illustrate that school and preschool contact patterns play an important role in the dynamics of varicella. Finally, our results provide baseline estimates of varicella and zoster incidence and morbidity for VZV vaccine effectiveness and cost-effectiveness studies.

Varicella is a disease caused by varicella-zoster virus. It is transmitted via the respiratory route, is highly communicable and mainly affects young children. An effective vaccine is now available, whose routine use is advised by health authorities in the USA and which can prevent severe disease, although breakthrough infections do occur. In deciding whether or not to include a vaccine in the routine vaccination schedule, knowledge of the morbidity of the disease in question is fundamental. Although reporting of varicella is compulsory in Catalonia, doctors only have to report the weekly number of cases diagnosed, and not their age distribution. Given that recent data on the prevalence of the infection in Catalonia according to age groups is available, it was considered that, using these data, an estimation of age-related incidence could be made.

The objective of the present study was to estimate the incidence of varicella in Catalonia on the basis of the available seroprevalence data. A curve was fitted to the observed prevalence and point prevalence estimates for all ages were obtained. The incidence was derived by smoothed prevalence for each of these age groups. Estimated variance of the estimated incidence was obtained by the delta method. Predicted prevalence in the 0–4 years age group was calculated by the smoothed prevalence.

The model that best fitted the sample prevalence was the exponential function. The estimated number of varicella cases in this study was 46419 (95% CI 40507–52270). As the population in Catalonia in 1996 was 6090040, the previous results give an incidence rate of 762·2 per 100000 persons/year with their 95% CI (666·1–858·3).

The method described may be applied to the study of incidence rates in relation to the prevalence of diseases if we accept that the infection produces permanent immunity; the risk of mortality is the same for infected and non-infected subjects and that the disease incidence and population remain constant in time.

We have evaluated the epidemiological evidence for an aetiological role of varicella zoster virus (VZV) infection in the development of multiple sclerosis (MS). A MEDLINE search of the English language literature for 1965–99 identified 40 studies. These studies were categorized as seroepidemiological (13), case-control (23), historical cohort (2) or ecological (2). One study used both case-control and historical cohort methodologies. Studies were then classified according to methodological rigour, using criteria derived from published guidelines for the epidemiological study of MS. There was a large variability in the quality of evidence. The five studies with the best methodology failed to show an increased risk of MS associated with varicella or zoster infections. At the present time there is insufficient evidence to support an important aetiological role of VZV infection in the development of MS.

The aim of this study was to describe the occurrence of shiga toxic genes (stx) in Norwegian sheep herds, and to identify herd management factors related to the occurrence of stx in herds. Faecal samples from 124 sheep-herds were collected at abattoirs in 1998. Pooled samples from lambs and from ewes were screened for stx by a PCR method directly on faeces. Of the 124 herds, 61 were positive for stx, giving an overall herd-prevalence of 49%. Twenty-one of the 61 positive herds were positive both in lamb and ewe samples, 24 only in lamb samples and 16 only in ewe samples. There was no difference in prevalence between regions. From the 21 herds positive both in lamb and ewe samples, stx encoding E. coli were detected in 18 herds using hydrophobic grid membrane filters and subsequent colony hybridization. Information about management factors was collected by telephone interviews. Having cattle at the same farm turned out to be a possible risk factor, with an Odds Ratio of 9·9 (CI 1·2 → ∞).

A serological study of hepatitis A was carried out in low-income areas scheduled for a major sanitation programme in Rio de Janeiro, Brazil. Blood spots were collected by finger puncture and transported on filter paper, and total antibodies to hepatitis A virus were detected by ELISA. Households were also interviewed to collect information on their environmental conditions and socio-economic status. A generalized linear model using a complementary log–log function was fitted to the data, using the logarithm of age as an explanatory variable to derive adjusted rate ratios (RR). The risk of infection was greater among households with 2–3 members per room (RR = 1·4; 95% CI = 1·04–1·8) or more than three per room (RR = 1·5; 95% CI = 1·2–2·0). People living on hilltops (RR = 1·5; 95% CI = 1·02–2·2), near to open sewers (RR = 1·2; 95% CI = 1·03–1·5) or lacking a kitchen (RR = 1·4; 95% CI = 1·08–1·9) were also at greater risk than others. The number of taps and water-using fittings in the house was associated with a protective effect (RR = 0·9 for each tap; 95% CI = 0·9–0·98). A significant protective association was found with maternal education but not with gender or household income. The results do not suggest a strong association with water quality. Ownership of a ceramic water filter was associated with a protective effect on the margin of significance, but the practice of boiling drinking-water was not, nor was the type of water source used. The results suggest that that the risk of infection with hepatitis A is determined by environmental variables in the domestic and public domains.

Nine isolates from pigs persistently infected with a recent Italian isolate of swine vesicular disease (SVD) virus, ITL/9/93, were collected sequentially over 121 days and were characterized antigenically and biochemically. There was an accumulation of amino acid (aa) substitutions in the capsid proteins throughout the carrier state that could be correlated with alterations in antigenicity in virus isolates collected late stage in infection. The aa substitutions detected mainly occurred in VP1 and antigenic changes were detected in late isolates both at antigenic site 1, resulting in loss of binding of Mab 4GO7, and at a closely located site which has not yet been named, recognized by Mab C29. In further experiments groups of pigs were exposed to a range of SVD viruses, but no virus was isolated beyond 16 days post infection (dpi) nor viral RNA detected beyond 42 dpi. Attempts to transfer infection to sentinel pigs introduced some time after initial infection of the original pigs were largely unsuccessful. The carrier state was established in only one out of five experimental infections of pigs with SVD virus and can therefore be considered a rare sequel to infection with SVD virus and is of limited significance in the epidemiology of the disease.

A study investigating the causes of rash diseases using systematic laboratory testing was conducted in Niterói, Rio de Janeiro, between January 1994 to April 1998. Sera from 327 patients were tested for evidence of anti-rubella virus, measles virus, human parvovirus B19 and dengue fever virus specific immunoglobulin IgM and anti-human herpes virus type 6 (HHV-6) IgG antibodies. A laboratory confirmed diagnosis was achieved in 71·3% of the cases investigated: dengue fever (33·0%), rubella (20·2%), parvovirus B19 (9·2%), measles (6·7%) and HHV-6 (2·1%). No diagnosis was established for 94 cases (28·7%). An outbreak of measles was detected during 1997, with a peak in September and October. All of the diseases studied here presented with clinical features similar to measles and classical symptoms were found in all measles confirmed cases. The large overlap of combinations of signs and symptoms seen in this study highlights the difficulties of diagnosing a rash illness on clinical grounds alone.

The prevalence of three waterborne zoonotic pathogens (Campylobacter sp., Giardia sp. and Cryptosporidium parvum) in rectal faecal samples from a random sample of adult beef cattle was determined. Management factors that may be associated with shedding of these organisms were examined. For Campylobacter sp. prevalence was 5·0%, and the number of females on the farm was positively associated with the proportion that tested positive. For Giardia sp. prevalence was 6·5%, and none of the management factors examined was significantly associated with the proportion in a herd testing positive. C. parvum was identified in 1·1% of samples. The length of calving season and whether any procedures were performed on the calves in the first 2 days of life were positively associated with the proportion that tested positive. We conclude that this sample of adult beef cattle represent a relatively limited threat to water supplies and subsequent disease transmission to humans from these pathogens.

To quantify the risk of human immunodeficiency virus (HIV) infection in children with tuberculosis (TB) a hospital-based, 1-year prospective, case-control study was performed in Addis Ababa, Ethiopia. Children with TB were compared to a control group of children admitted for elective surgery. The control group was also compared to a recent census of the background population. The crude odds ratio for HIV infection was 8·6 (95% CI 2·2–73). After adjustment for possible confounders in a multivariate regression model, the odds ratio for HIV infection in children with TB was found to be 12·7 (95% CI 2·9–55). Of several independent determinants of TB assessed in the study, this association was the strongest. Until HIV transmission has reached its peak, an increasing burden of dual infection among Ethiopian children is to be expected.

In Palestine, there has been an increase in the reported incidence of acute hepatitis A virus (HAV) infection since 1995. Since overt clinical disease occurs only among adults, questions were raised whether or not a shift in the epidemiology of HAV has occurred. This is generally characterized by a decrease in the overall incidence rate and a shifting in the mean age of infection towards adolescence and early adulthood. The need for a vaccination programme is being discussed. To resolve this issue, we examined the prevalence of anti-HAV in a representative sample of 396 school children in the Gaza Strip. The prevalence of anti-HAV was 93·7% (95% CI: 91·3, 96·1%). Stratifying the prevalence by age showed that 87·8% (95% CI: 78·6, 97%) were HAV antibody positive by the age of 6. By the age of 14, almost 98% (95% CI: 92·7, 100%) were HAV antibody positive. This means that the majority of HAV infection is still taking place in early childhood, when it is usually asymptomatic and of little clinical significance. The results refuted the shifting epidemiology theory and we recommend that a vaccination programme against HAV infection is not yet needed. Alternative explanations for the increase in reported cases are discussed.

To improve our knowledge for future hepatitis A virus (HAV) vaccination strategies we carried out a multicentre study on naturally acquired immunological protection against HAV in patients with chronic hepatitis in Italy. We enrolled 830 consecutive patients with chronic hepatitis on their first observation at one of the six Italian liver units participating in the study. Six hundred and fifty-eight patients (79·3%) were positive for total anti-HAV and 172 (20·7%) were negative. The anti-HAV negative patients were younger (median age 33, range 11–78) than the anti-HAV positive (median age 56, 18–87). There was a higher prevalence of cases with circulating anti-HAV among the 508 patients residing in southern Italy than in the 322 residing in northern Italy (88·8% vs. 64%, P < 0·001). No significant difference in the anti-HAV prevalence was observed between patients from northern Italy and those from southern Italy aged 0–30 years or in those over 60 years, while in those 31–60 years old there was a higher prevalence of anti-HAV positive patients from southern Italy (90·2% vs. 65·8%, P < 0·0001). Of the patients with liver cirrhosis in this study, only 3 of the 26 (11·5%) from northern Italy and 8 of the 228 (3·5%) from southern Italy had no immunological protection against HAV infection. The data suggest that the number of patients with chronic liver disease without naturally acquired immunity against HAV is substantial in Italy, particularly in the north of the country, and that new vaccination strategies are needed.

The epidemiological, clinical and therapeutic features of HIV disease diagnosed in 41 immigrants from outside of the European Union (EU), were compared with those of 123 Italian and EU patients, in a cross-sectional case-control study, with individuals matched according to age and gender. In total 4·15% of our patients came from outside of the EU (51·2% of them from subsaharan Africa), with a proportional predominance of females, and heterosexual and perinatal transmission of HIV disease (P < 0·0001 and P < 0·02, respectively). Compared with Italian and EU subjects, patients coming from abroad had a shorter duration of known HIV infection (P < 0·001), but only some subjects were aware of their HIV disease prior to immigration, or acquired HIV infection only after coming to Italy (14·6% and 12·2%, respectively). No cases of HIV-2 infection or co-infection were detected in either study group. Compared with controls, patients coming from outside of the EU had a comparable clinical and immunological status, and had similar antiretroviral therapy, which was administered earlier (P < 0·0001), and proved better tolerated (P < 0·04), than in Italian and EU subjects. The apparently more limited virological response (as expressed by a higher mean plasma viral load, and a lower rate of viral suppression at the last visit; P < 0·001 and P < 0·05, respectively), was probably a bias due to the shorter mean overall follow-up time (P < 0·0001), and the shorter mean duration of antiretroviral treatment (11·1±2·2 months of immigrants vs. 16·2±6·7 months of controls; P < 0·0001).

The epidemiology and transmission dynamics of sheep scrapie is as yet poorly understood. Here we present a theoretical analysis of the transmission dynamics within a sheep flock, concentrating on how persistence properties depend on transmission scenario and flock size. Patterns of disease persistence and extinction are studied analytically using branching-process approximations and numerically using stochastic model simulations. For a given basic reproduction number, disease extinction is most likely when late-stage infected animals are responsible for most of the transmission. This effect can be understood in terms of aggregation in the distribution of the number of secondary infections arising from a single primary infection. The presence of an environmental reservoir reduces the probability of extinction.

Our objectives were to assess the prevalence of anti-hepatitis A (HAV) antibodies in Spanish travellers to developing countries and to carry out a cost analysis to allow the comparison of two vaccination strategies. Adult subjects were selected from among travellers to developing countries. Information was obtained on age, sex, destination, previous vaccination against HAV and having received immunoglobulin. Blood specimens were obtained for anti-HAV antibody determination. A total of 485 travellers were studied. The prevalence of anti-HAV antibody was 30·5% (95% CI 26–35). Antibody prevalence was inversely correlated with age: 9·8% in 18–25 years of age, rising to 75·4% in those 41–55 years of age. Cost analysis determined that the critical value of prevalence for vaccination with HAV vaccine was 37·5%. It was concluded that the youngest Spanish travellers lack anti-HAV antibodies. Vaccination without screening in those [les ] 35 years of age and screening before vaccination for those > 35 years, are the preferred alternatives.

We used spoligotyping to study 500 randomly selected pretreatment Mycobacterium tuberculosis (MTB) strains isolated in Hong Kong during the 2 year period 1998–9. It was found that amongst all MTB strains studied, the ‘Beijing’ genotype strains were highly prevalent in our geographic area, representing about 70% of the isolates. Unlike previous observations in Vietnam, no significant associations were found either between ‘Beijing’ genotype strains and all other anti-tuberculosis drug resistance phenotypes, or with particular patients' age groups, except for a weak association with isoniazid susceptibility. Eighteen of these strains exhibited spoligotype patterns that were similar but not identical to the ‘Beijing’ specific pattern. This is the first geographical area where genetic diversity among ‘Beijing’ genotype of MTB strains has been observed on this scale.

To study whether African-Americans are less likely than whites to present with cryptosporidiosis as an AIDS-defining condition (ADC), a case-control study was conducted using a large, population-based surveillance registry of AIDS patients in California. Data from January 1980 through June 1999 were analysed using risk factor stratification and multivariate logistic regression to evaluate confounding by other risk factors such as gender, injection drug use (IDU), CD4 counts, age and sexual orientation. Cases included 1373 subjects with cryptosporidiosis as an ADC and controls included 97419 subjects with other ADC. The results indicate a significantly lower risk for presentation with cryptosporidiosis as an ADC among African-Americans compared with whites (OR vs. whites = 0·5, 95% CI 0·4, 0·7). Additionally, there is evidence that heterosexuals are less likely than homosexual/bisexual males to present with cryptosporidiosis (OR = 0·5, 95% CI 0·4, 0·7). Our analyses also suggest a decreasing risk with increasing age. The possibility that there may be biologic factors or differential lifetime exposures that account for the difference between the racial/ethnic groups merits further investigation.