The unexpected appearance of fatal encephalitis in six elderly people living in New York in 1999, heralded the re-birth of arbovirology in the United States of America. The subsequent rapid spread through North America and impact of the disease on humans, birds, horses and a wide range of other species including alligators and frogs, has brought West Nile virus (WNV) to the attention of governments and the media, worldwide. The response of the public in the United Kingdom has not been hysterical, despite being fuelled by press reports that scientists have demonstrated the presence of WNV antibodies in birds in the UK. Nevertheless, concern has been expressed by government bodies either directly or indirectly connected with the potential health problems that could arise if WNV was introduced and caused the same degree of morbidity and mortality as that seen in the USA. Is the concern justified and are we likely to see significant health problems associated with WNV if this virus is confirmed to be present and circulating amongst birds in the UK? In this review I shall try to put the virus in its true context and assess the risks that WNV might pose both to animals and humans in the United Kingdom.

In 1999–2000 we conducted a one-year, retrospective population-based survey in Norway to estimate the incidence of gastroenteritis and study the association with selected exposures. A self-administered questionnaire was mailed to 3000 persons selected at random from the population registry, with 250 persons being contacted each month. The response rate was 61%. The incidence of acute gastroenteritis was 1·2 per person-year. The incidence was higher for women than for men. Of the total of 171 cases, 29 (17%) consulted a physician, 13 (8%) reported that a stool sample was taken, and 7 (4%) were admitted to hospital. Among children aged less than 15 years, drinking water from a private water supply was associated with illness, while using chlorinated water was protective. Among adults aged 20–40 years, travelling abroad was associated with illness. The incidence in our survey is similar to rates found by FoodNet in United States.

Blood samples were taken from 50 finishing pigs at 90–105 kg in each of 59 randomly selected farrow-to-finish herds. The sera were tested for antibodies to Salmonella enterica by the Danish mix-ELISA. Samples with an optical density of >10% were considered to be positive. Associations between the odds of seropositivity of pigs and possible risk factors were evaluated in multivariable logistic regression models. The results of the analysis indicated that pigs fed non-pelleted dry or wet ration had 11 (P=0·0004) or 9 (P=0·02) times, respectively, lower odds of seropositivity than those fed pelleted ration. The risk of seropositivity was 4 (P=0·0006) times higher in pigs fed a combination of chlortetracycline, procaine penicillin and sulphamethazine during fattening than in those fed an approved growth promotor or a probiotic.

Salmonella enterica serotype Enteritidis is an important serovar comprising 76% of salmonella isolates in Portugal in 2001.

For better understand the epidemiology of salmonellosis, a total of 47 isolates of S. Enteritidis phage type (PT) 1b and 6a were analysed by pulsed-field gel electrophoresis (PFGE) and genomic DNA was subjected to macro restriction with XbaI. For PT1b isolates, only three different patterns were observed, and PT6a showed a total of 10 digestion patterns. Curiously, the main pattern among PT1b isolates seams quite similar to main pattern of PT6a isolates, but when the two patterns were analysed with Bionumerics, we observed that they exhibited some differences. It was concluded that, in 2001, there was one predominant pattern for PT1b and PT6a and, possibly, we were in presence of clonal strains that exists all over the country.

The survey of Vibrio cholerae O1 in marine area was carried out in the Port of Osaka, Japan in 1987–2001, and 51 V. cholerae O1 strains were isolated. All strains were identified to be of El Tor biotype, Ogawa serotype and classic Ubon Kappa-phage type, and were cholera toxin (CT)-negative and CT gene-negative. In order to clarify certain ecological aspects of V. cholerae O1 in the marine environment of the temperate zone, we performed molecular analysis of the isolated strains using pulsed-field gel electrophoresis (PFGE) with NotI and SfiI restriction enzymes. We found the indistinguishable strains by DNA analysis using PFGE with strains passed for 1 year, and also found the closely related strains with that passed for 3 and 12 years. Those results indicated that V. cholerae O1 can survive over one winter at least, and that it survives in marine water for a long time by undergoing continuous mutation.

Occurrences of ciguatera fish poisoning (CFP) and Vibrio cholerae infected patients in Hong Kong were reviewed for the 13-year period 1989–2001. Peak activity of CFP preceded peak activity of cholera in nine of the years except in 4 years (1990, 1991, 1992, 1996) where it was observed that the total number of cholera cases were all less than or equal to five per year (P<0·05). Average time interval was 2·4 months between peaks of CFP and Vibrio cholerae outbreaks. Findings suggested that the factors that affect cholera and ciguatera occurrences may not be operating in some years but when they are operating, they will affect both cholera and CFP. CFP peaks have consistently occurred before Vibrio cholerae peaks in our locality so much so that the occurrence of the latter can now be almost accurately predicted since 1998. CFP peaks served as an early warning for public measures to be in place before occurrence of cholera outbreaks.

Pneumonia causes significant morbidity and mortality in Aboriginal populations in Australia's Northern Territory (NT). Kava, consumed in Arnhem Land since 1982, may be a risk factor for infectious disease including pneumonia. A case–control study (n=115 cases; n=415 controls) was conducted in 7001 Aboriginal people (4217 over 15 years). Odds ratios (OR) were calculated by conditional logistic regression with substance use and social factors as confounders. Pneumonia was not associated with kava use. Crude OR=1·26 (0·74–2·14, P=0·386), increased after controlling for confounders (OR=1·98, 0·63–6·23, P=0·237) but was not significant. Adjusted OR for pneumonia cases involving kava and alcohol users was 1·19 (0·39–3·62, P=0·756). In communities with longer kava-using histories, adjusted OR was 2·19 (0·67–7·14, P=0·187). There was no kava dose–response relationship. Crude ORs for associations between pneumonia and cannabis use (OR=2·27, 1·18–4·37, P=0·014) and alcohol use (OR=1·95, 1·07–3·53, P=0·026) were statistically significant and approached significance for petrol sniffing (OR=1·98, 0·99–3·95, P=0·056).

A cluster of three cases of listeriosis cases occurred against a background of endemic listeriosis in Western Australia. Human and environmental isolates of Listeria monocytogenes obtained during the outbreak investigation were rapidly subtyped by automated ribotyping using an EcoRI protocol and a RiboPrinter®. DNA macrorestriction analysis by pulsed-field gel electrophoresis (PFGE) was used to confirm the relatedness of isolates. Serogroup 1/2 predominated among the food samples and the four clinical isolates from the outbreak cluster were also of this serogroup. All isolates from chicken material were serogroup 1/2 and indistinguishable by ribotype pattern. PFGE subdivided strains of this ribotype into four subtypes. The preliminary analysis had an immediate impact on hypothesis generation, environmental health investigations, environmental specimen collection and initial control measures. Sufficient typing data to guide environmental health and disease control initiatives was generated in less than one week by combining automated ribotyping with PCR-based detection of L. monocytogenes in suspect foodstuffs and an L. monocytogenes DNA probe. There were no further cases of bacteriologically confirmed listeriosis in Western Australia for six months after completion of the investigation.

We evaluated improvements made to the mandatory notification surveillance system for Legionnaires' disease in France by estimating its sensitivity in 1995 and 1998 using a repeat capture–recapture method. A case of Legionnaires' disease was defined as a person treated for pneumonia in whom legionella had been detected. Patient details were collected from (1) mandatory notifications; (2) the National Reference Centre for Legionella; (3) a postal survey of all hospital laboratories. The three sources were cross-matched and 715 individual cases were identified. A log-linear model, which included an interaction term between mandatory notifications and both the National Reference Centre and Laboratory sources, provided an estimated total of 1124 cases (95% CI 973–1275) in 1998, a twofold increase compared with 1995. The sensitivity of the surveillance system improved from 10% in 1995 to 33% (95% CI 29–38%) in 1998. Capture-recapture methods are important tools in the evaluation of surveillance systems.

The incidence rate of giardiasis in New Zealand is one of the highest among developed countries, peaking in the 1–4 year age group. A case–control study was undertaken to identify risk factors for giardiasis among Auckland children under 5 years of age. The exposure history of 69 cases and 98 controls were analysed. Ninety-five per cent cases and 86% controls used water from the Auckland Metropolitan mains (AMM) supply for domestic purpose, 44 cases and 42 controls swam and 59 cases and 54 controls wore nappies. Children wearing nappies were at significantly increased risk of the disease (OR=3·0, 95% CI=1·01–8·9), as were those from households which had more than one child wearing a nappy (6·5, 1·8–23·4). The Auckland metropolitan mains water supply was associated with a reduced risk compared to other drinking water sources. Significantly increased risks were also associated with drinking water consumed away from home (4·7, 2·2–10·1), swimming at least once a week (2·4, 1·1–5·3) and travelling domestically (2·5, 1·03–6·0). The study identified vulnerable groups and modifiable risk factors for diarrhoeal diseases, particularly Giardia infection. Nappy wearing was an independent risk factor for infection. Further study is advocated to ensure better protection of public health, especially for children.

In a study to estimate the frequency of Cryptosporidium infections in Switzerland, stool samples from patients found to be positive for Cryptosporidium spp. by modified Ziehl–Neelson staining and fluorescence microscopy were used for genotyping experiments. With 9 of 12 samples, DNA extraction and subsequent genotyping was successful. All Cryptosporidium-isolates belonged to the bovine genotype. In one stool sample, two strains of Cryptosporidium were demonstrated, suggesting a mixed infection. In comparison with reference strains from calves, one of the isolates showed a full sequence identity and the other a similarity of 97·5%. The fact that only bovine genotypes were detected suggests, that cryptosporidiosis must primarily be considered as a zoonotic disease in Switzerland. This is in contrast to other countries, where the human genotype of C. parvum was shown to dominate the epidemiological situation. The results of our study are supported by the previous finding, that two of the analysed strains originated from patients who used to consume raw milk or raw cream, a known risk factor for cryptosporidiosis.

Because non-name-based case registries have recently been used for reporting human immunodeficiency virus infection, this study attempted to define the sensitivity, specificity and accuracy of case registry matches using non-name-based registries. The AIDS, sexually transmitted disease (STD), and tuberculosis (TB) case registries were matched using all available information to establish the standard. The registries were then matched again using five increasingly less specific criteria to compare sensitivity, specificity and accuracy. The registries were then also transformed into non-name-based codes as if they were the HIV registry and matched again. With name-based registries, sensitivities increased as the matching criteria became less exacting, while the accuracy declined slightly. Specificities remained close to 100% due to the relatively small number of matched cases. Results from matches of non-name-based registry matches were similar to those of the name-based registry matches. Non-name reporting can be used for data matching with acceptable accuracy.

The aims of the study were to compare the burden of varicella and herpes zoster in Australia. No national surveillance exists for varicella or herpes zoster. We used hospital morbidity data from 1993–9 and pharmaceutical prescribing data from 1995–9.

In the financial year 1998/99, there were 4718 hospitalizations for zoster compared to 1991 for varicella. For varicella the mean age of patients was 15 years compared to 69 years for zoster. The mean length of stay in hospital was 4·2 days for varicella and 12·7 days for zoster. Varicella accounted for 8396 (3726 with principal diagnosis varicella) bed days compared to 26266 (5382 with principal diagnosis of zoster) for zoster. The in-hospital case-fatality rate was 0·4% for varicella and 1% for zoster. In 1999, 59200 community-based cases of zoster were treated with antivirals. We estimate that 157266 cases of zoster occurred in the community in 1999, a rate of 830 per 100000 population.

Herpes zoster has a higher burden of disease than varicella, and must be a component of disease surveillance in order to determine the full impact of vaccination on the epidemiology of varicella zoster virus (VZV).

Clinical descriptions of Epstein–Barr virus (EBV) positive infectious mononucleosis (IM) are rare and their results are inconsistent. Over a 4-year period, we prospectively studied 590 young adults with clinically suspected IM, all of whom were tested for the presence of EBV IgM antibodies. We investigated the demographical, clinical and laboratory features of subjects with positive EBV IgM serology and heterophile antibodies. Contrary to previous studies, we found a seasonal disease pattern with a peak incidence during summer months, and a lower-than-expected prevalence of lymphadenopathy (88·9%), leucocytosis (46·2%), atypical lymphocytosis (89·2%) and elevated liver enzymes (57·9%). The prevalence of hyperbilirubinemia was relatively high (14·9%). The classic triad of fever, sore throat and lymph-adenopathy had relatively low sensitivity (68·2%) and specificity (41·9%) for EBV infection. Our study provides a complete and updated description of the clinical and laboratory presentation of laboratory confirmed IM, which is important for both clinicians and epidemiologists.

Six countries (Denmark, England and Wales, France, Germany, Italy and the Netherlands) conducted large serological surveys for mumps, in the mid-1990s, as part of the European Sero-Epidemiology Network (ESEN). The assay results were standardized and related to the schedules and coverage of the immunization programmes and the reported incidence of mumps. Low incidence of disease and few susceptibles amongst adolescents and young adults was observed in countries with high mumps vaccine coverage (e.g. the Netherlands). High disease incidence and large proportions of mumps virus antibody negative samples in adolescent and young adult age groups was noted in countries with poor vaccine coverage (e.g. Italy). The build-up of susceptibles in older children and adolescents in England and Wales, France, the former West Germany and Italy indicate the possibility of further mumps outbreaks in secondary school environments. To control mumps in western Europe, current MMR immunization programmes will need to be strengthened in a number of countries. Sero-surveillance of mumps is an important component of disease control and its usefulness will be enhanced by the development of an international mumps standard.

To obtain insight into mumps immunity 9 years after introduction of vaccination in The Netherlands, antibodies were measured in a national sample (n=8298) and in clustered religious groups with low vaccine acceptance (n=254). All sera were tested by indirect ELISA, and agreement with neutralization assay was assessed in a subsample (n=623). Overall seroprevalence in the adult age groups in the national sample was 96·2% (95% confidence interval 95·4–97·0%). Seroprevalence was somewhat lower in the vaccinated age groups, but still sufficient to maintain herd immunity. After the first dose of vaccine, an increase up to age three years to 93·2% (89·8–96·6%) and a subsequent decline in prevalence to 88·9% (81·7–96·0%) at age 7 years was seen. Seroprevalence in those eligible for two vaccinations was 94·4% (91·3–97·4%). In the religious groups, seroprevalence was generally lower in the age group 1–4 years (30% (18–95%)) than in the national sample, but similar in the older age groups. Seroprevalence as estimated by neutralization assay was only slightly lower for all age groups [ges ]1 year. Therefore, the indirect ELISA is a reliable method for measuring mumps virus-specific antibodies in population-based studies. However, to allow for inter-laboratory comparison, international unitage should be developed.

Acute flaccid paralysis (AFP) surveillance data from India were analysed to examine sensitivity of poliovirus isolation from stool specimens and the added sensitivity obtained from collection of a second stool specimen. Analysis was restricted to Indian AFP cases, 1998–2000, with two adequate stool specimens. The proportion of cases confirmed with wild poliovirus isolation by the second specimen only was calculated, regardless of specimen quality. Overall specimen sensitivity (1998–2000) was 81% using the first specimen, 78% using the second, and 96% using both. Sensitivity increased from 1998 to 2000, with slightly higher sensitivity each year for the first specimen. The second specimen increased sensitivity by 15% overall and contributed more when the first specimen was collected late or was in poor condition. As wild poliovirus disappears, increased sensitivity provided by a second stool specimen may reduce the risk of missing circulating virus.

Rotaviral associated disease of infants in the UK is seasonal and infection in adults not uncommon but the relationship between these has been little explored. Adult sera collected monthly for one year from routine hospital samples were screened for the presence of anti-group A rotavirus immunoglobulin M class antibodies as a marker of recent infection. Anti-rotavirus IgM was seen in all age groups throughout the year with little obvious seasonal variation in the distribution of antibody levels. IgM concentrations and the proportion seropositive above a threshold both increased with age with high concentrations consistently observed in the elderly. Results suggest either high infection rates of rotavirus in adults, irrespective of seasonal disease incidence in infants, IgM persistence or IgM cross-reactivity. These results support recent evidence of differences between infant and adult rotavirus epidemiology and highlight the need for more extensive surveys to investigate age and time related infection and transmission of rotavirus.

An outbreak of gastroenteritis affected a school attended by children aged 4–11 years. Epidemiological features suggested this was due to Norwalk-like virus (NLV) and this was confirmed by polymerase chain reaction (PCR). Nucleotide sequence analysis of the PCR amplicons revealed identical strains in all five positive stool samples. Pupils were significantly more likely to become ill following an episode of vomiting within their classroom (adjusted odds ratio 4·1, 95% CI 1·8–9·3). The times from exposure to illness were consistent with direct infection from aerosolized viral particles where exposure to vomiting was high.

Cleaning with quaternary ammonium preparations made no impact on the course of the outbreak. However, the outbreak stopped after the school closed for 4 days and was cleaned using chlorine-based agents. This study confirms the importance of vomiting in the transmission of NLV and provides evidence that direct infection with aerosolized viral particles occurs.

An outbreak of gastroenteritis due to Norwalk-like virus (NLV) affecting approximately 500 people occurred in a Swedish ski resort during February–March 2002. Epidemiological investigations were performed on cohorts of schoolchildren, permanent residents and skiers visiting the area. Attack rates were respectively 39·7, 29·9 and 38·5%. Drinking un-boiled water originating from one of the three communal water systems was a significant risk factor for all groups. For schoolchildren, the risk of illness increased with increasing amount of water consumed. Nine of 12 stool samples of patients analysed tested positive for NLV. The water tested negative for indicator bacteria and results of NLV tests were inconclusive. In the absence of microbiological findings, the environmental authorities were reluctant to act based on the epidemiological analysis alone, and intervention was delayed until mid-April, following the discovery of a crack in a sewage pipe 10 m from the well.