When applicable, case-crossover studies may be quicker and cheaper to complete than case-control studies. Because time is a major issue in outbreak investigations, we evaluated the interest of this design during a continuous common source food-borne outbreak of salmonellosis for which the vehicle (hamburgers) was also implicated by environmental and laboratory investigations. Seventeen of the 35 cases identified in the outbreak were included in the study according to the availability of menu records with detailed information on food consumed at each meal. Food exposures during a 3-day risk period before onset of illness were compared to those of a control time-interval of the same duration that preceded the risk period by two days. Seventy-seven per cent of the cases (13/17) had consumed hamburgers in the three days preceding onset of illness compared with 29% (5/17) during the control period (P=0·04, odds ratio=5, 95% CI: 1·1–46·9). In this investigation the case-crossover design proved to be a useful and efficient alternative to the case-control approach. However, further evaluation of this design in outbreak investigation is needed.

A total of 102 Escherichia coli strains belonging to serogroups O127 and O142 were examined for genotypic and phenotypic characteristics. The most frequent serotypes found were O127[ratio ]H21, O127[ratio ]H40 and O142[ratio ]H34. The virulence properties were evaluated by adhesion to HeLa cells and hybridization with gene probes for diarrhoeagenic E. coli. Most strains in the two serogroups were categorized as enteropathogenic E. coli, but enteroaggregative E. coli was also detected in both serogroups. All strains that carried the eae sequence presented the LEE region inserted in selC. Five ribotypes were detected in serogroup O127 and four in serogroup O142 and a correlation between serotypes and ribotypes was observed mainly in serogroup O142.

Group B streptococcal isolates (n=159) from the three Dublin maternity hospitals, were serotyped and analysed for the bac, bca, hylB, pepB, and rib genes. The serotype distribution of the isolates was Ia, 19·5%; Ib, 18·9%; II, 10·7%; III, 29·5%; IV, 1·9%; V, 15·1%; non-typeable, 4·4%. There was a statistically significant association between the serotype and invasive status (carriage or infection) of isolates (P<0·005), but no significant association between serotype and degree of invasiveness was demonstrated. The presence or absence of each analysed gene was not associated with the invasive status of isolates. Statistically significant associations were revealed between bca and hylB (IS1548) (P=0·0004) and between bac and bca (P=0·0l4). The bac, bca, hylB (IS1548) and rib genes and the numbers of tandem repeats in the bca gene showed significant associations with serotype. Almost 50% of serotype III isolates possessed at least one of the bac and bca genes and 55–65% of strains of serotypes Ia, Ib and II possessed the rib gene. Most serotype III isolates had IS1548 in their hylB genes. Serotype Ib was the only serotype in which more than half of the strains contained more tandem repeats in the bca gene than the overall mean for the GBS population studied of 7·4 repeats. These findings indicate that some previously reported associations between putative virulence factors and GBS disease require further study and clarification.

The Veterans Health Administration (VHA) of the Department of Veterans Affairs tracks legionella disease in the system of 172 medical centres and additional outpatient clinics using an annual census for reporting. In fiscal year 1999, 3·62 million persons were served by the VHA. From fiscal year 1989–1999, multiple intense interventions were carried out to decrease the number of cases and case rates for legionella disease. From fiscal year 1992–1999, the number of community-acquired and healthcare-associated cases decreased in the VHA by 77 and 95·5% respectively (P=0·005 and 0·01). Case rates also decreased significantly for community and healthcare-associated cases (P=0·02 and 0·001, respectively), with the VHA healthcare-associated case rates decreasing at a greater rate than VHA community-acquired case rates (P=0·02). Over the time of the review, the VHA case rates demonstrated a greater decrease compared to the case rates for the United States as a whole (P=0·02). Continued surveillance, centrally defined strategies, and local implementation can have a positive outcome for prevention of disease in a large, decentralized healthcare system.

The number of registered leprosy patients world-wide has decreased dramatically after extensive application of WHO recommended Multiple Drug Therapy (MDT). The annual number of new cases has, however, been almost unchanged in several populations, indicating that the infection is still present at community level. Nasal carriage of Mycobacterium leprae DNA was studied in Lega Robi village in Ethiopia. MDT had been applied for more than ten years, and 718 residents over 5 years old were eligible for the study. During the first survey nasal swab samples were collected from 664 (92·5%) individuals. The results of a Peptide Nucleic Acid-ELISA test for M. leprae DNA interpreted by stringent statistical criteria were available for 589 (88·7%) subjects. Thirty-five (5·9%) individuals without clinical signs of leprosy were positive for M. leprae DNA. Seven PCR positive individuals lived in a household where one or two other members were also positive for M. leprae DNA. During a second survey 8 (4·6%) of 175 interpretable PNA-ELISA tests were positive. Of 137 individuals tested twice, only two were positive on both occasions whereas 10 were PCR positive only once. The study confirms the widespread distribution of M. leprae DNA in healthy individuals. The feasibility of curbing possible transmission of subclinical infection needs further consideration.

Instituting air travel restrictions to slow the geographical spread of smallpox cases would have significant consequences and present serious logistical concerns. Public health decision makers must weigh the potential benefits of such restrictions against their negative impact. The goal of this research is to provide a basic analytical framework to explore some of the issues surrounding the use of air travel restrictions as a part of an overall containment strategy. We report preliminary results of a compartmental model for the inter-city spread of smallpox cases resulting from US domestic air travel. Although air traffic can be halted within hours as was shown following the terrorist attacks of 11 September 2001, these results suggest that the consequences of halting domestic air travel may not be outweighed by public health benefits.

This study aimed to evaluate the relationship between HSV-2 infection and several socio-demographic and sexual practices of Mexican and Central American female sex workers (FSWs) in the Soconusco region in the State of Chiapas, Mexico. A cross-sectional study was carried out based on a sample frame of bars where FSWs were active in the Soconusco region. FSWs consented to investigations and answered a questionnaire and provided a blood sample for specific HSV-2 antibody analysis.

One hundred and sixteen bars were studied and 484 women were interviewed. The overall frequency of HSV-2 infected women was 85·7%. Variables that reflected exposure to HSV-2 were significantly associated with the frequency of the infection. Additionally, variables such as education and country of origin were significantly associated with HSV-2 infection. These results suggest that this infection is highly endemic in the Soconusco, posing a health risk for the study population.

The aim of this population-based retrospective study was to determine the incidence of hospitalization for community-acquired, laboratory-confirmed respiratory syncytial virus (RSV) infection in an unselected paediatric population from southern Europe. The study was performed in an area with 15700 children aged less than 5 years attended by a single hospital. The presence of RSV in nasopharyngeal aspirates from children with acute respiratory infection treated in the hospital was investigated in four seasons (July 1996–June 2000). A total of 390 episodes of hospitalization for RSV infection were detected and 83·3% of the children were aged less than 1 year old. The annual hospitalization rate was 37/1000 for infants aged less than 6 months and 25/1000 for those aged less than 1 year. During the study period, 2·5% of the infants younger than 1 year and approximately 5% of those younger than 3 months were hospitalized for RSV infection. The mean length of hospital stay was 5·9 days. Seven per cent of the patients required admission to the intensive care unit and more than half of these children were aged less than 1 month. In Spain, community-acquired RSV infection is a highly frequent cause of hospitalization in young children, especially in those aged less than 1 year. Prevention of RSV infection, through the development of vaccines and/or other strategies, should be a public health priority.

We investigated primary human herpesvirus-6 and -7 (HHV-6, HHV-7) infections as a cause of rashes incorrectly diagnosed as measles in Brazilian children. Sera from 124 patients, aged 4 months to 17 years, from the states of Rio de Janeiro and Espírito Santo, in whom measles, rubella and parvovirus B19 infections had been excluded, were studied using indirect immunofluorescence antibody avidity tests; 38 (31%) had evidence of primary HHV-6 and/or HHV-7 infections. Twenty four children had primary HHV-6 infection, either recent or coincident with the rash, and similarly 31 had primary HHV-7 infection. Remarkably, almost half (17) of primary infections were dual HHV-6 and HHV-7 infections with the majority, 12 (71%), in children less than 1 year old. HHV-7 infection occurred earlier than previously reported, perhaps due to socioeconomic and tropical conditions in this region of Brazil, and thus coincided with the HHV-6 infections. This study also highlights the difficulties of diagnosing a rash illness on clinical grounds alone.

Japanese encephalitis (JE) is a serious health problem in the southwestern region of Nepal. Serological diagnostic kits for routine diagnostic use in this region have not been available. This study was performed to examine if the particle agglutination (PA) assay for Japanese encephalitis virus (JEV) IgM could be applicable to the samples collected in Nepal and also to evaluate the accuracy of clinical diagnosis of JE. One hundred and ninety-three blood samples were collected from the patients clinically diagnosed with JE or other infectious diseases in the JE-endemic, southwestern region of Nepal, in 2000. The PA assay was performed on these 193 serum samples and the results were compared with those by IgM-capture ELISA. Eighty-six samples were IgM-positive by the PA assay, and 71 of 86 were also positive by IgM-capture ELISA (sensitivity, 99%; specificity, 88%; positive predictive value, 0·82; negative predictive value, 0·99). These results suggest that the PA assay is a simple, reliable and useful diagnostic test to support clinical diagnosis in rural hospitals of Asia including Nepal.

The aims of this descriptive study were to confirm the high incidence of subacute sclerosing panencephalitis (SSPE) previously reported from Papua New Guinea (PNG) and to relate SSPE to previous measles vaccination and measles illness. From February 1997 to April 1999 we diagnosed a total of 55 patients with SSPE at Goroka Base General Hospital in Eastern Highlands Province (EHP) of PNG. The diagnosis was based on high cerebrospinal fluid and serum measles virus antibody titres with progressive neurological disorder and myoclonic jerks. Of these 55 patients 42 were from EHP, including 32 whose onset was in the 2-year period 1997–1998. The annual incidence of SSPE in EHP in these 2 years was 98 per million population under 20 years of age, the highest ever reported. This incidence was more than ten times higher than the highest incidence in the prevaccine era reported from elsewhere. The mean age of onset of SSPE was 7·7 years (range 2·8–14·8 years) and the interval between measles and the onset of SSPE, where known, had a mean of 5·9 years and a range of 2·5–11·1 years. Among the SSPE patients 19 had a documented history of measles vaccination. Eight of these 19 also had documentation of previous measles illness; of these, seven were vaccinated after the development of measles and one was vaccinated 20 days before measles illness. Two non-SSPE children received vaccination twice which was documented and subsequently developed measles which was also substantiated by documentation. Two patients with SSPE yielded amplified nucleotide sequences of measles virus that were different from any of the vaccine strains. We found no evidence to implicate measles vaccination in the development of SSPE.

A cross-sectional study of 694 children aged 2 to 45 months selected from 30 clusters throughout the city of Salvador, Bahia (pop. 2·3 million) was carried out as part of a longitudinal study of diarrhoea in order to identify risk factors for infection with Giardia duodenalis. Variables studied included three social and demographic factors (such as mother's education and marital status), five relating to the peri-domestic environment (rubbish disposal, open sewers, paving of the street), seven relating to the home itself (house construction, susceptibility to flooding, water supply and sanitation) as well as a score for hygiene behaviour based on structured observation. After multivariate analysis using a hierarchical model, only four significant risk factors were found: (a) number of children in the household under five years (b) rubbish not collected from the house (c) presence of visible sewage nearby, and (d) absence of a toilet. All four were significant at the 1% level.

Between 1992 and 1999, 93 cases of blastomycosis, including 25 laboratory confirmed cases, were identified in Missouri (annual incidence, 0·2/100000 population). Mississippi County in southeastern Missouri had the highest incidence (12/100000) with a much higher rate among blacks than whites in this county (43·2/100000). The mortality rate, 44% was also higher among blacks. To determine risk factors for endemic blastomycosis, a case-control study was conducted among southeastern Missouri residents. Independent risk factors for blastomycosis were black race and a prior history of pneumonia. No environmental exposures or socioeconomic factors were significantly associated with increased risk. The increased risk among blacks may possibly be related to genetic factors, but further studies are needed to clarify this. However, heightened awareness of the disease and a better understanding of the risk factors are important and may lead to earlier diagnosis and start of treatment, possibly improving outcome.

During the period January 1998–December 2001, all Danish broiler flocks were monitored bacteriologically for thermophilic campylobacters and isolates were stored at −80 °C. Six neighbouring broiler farms in a small community were selected for detailed examination of all Campylobacter jejuni isolated (n=180) from these farms during 1998–2000 using Penner serotyping and pulsed-field gel electrophoresis (PFGE). The area and the farms were selected according to their prevalence of campylobacter so that both farms with low and high frequencies of campylobacter positive flocks were included in the study. The frequency of campylobacter positive flocks on the six farms ranged from 24·5 to 72·7%. One hundred and eighty of the isolates were C. jejuni (included in this study), 14 isolates were C. coli whereas 7 isolates belonged to other species but were not further identified. By serotyping of all C. jejuni 56 isolates (31·5%) were assigned to the 4-complex, 32 isolates (18·0%) to serotype 2, 12 isolates (6·7%) to serotype 11, and 11 isolates (6·2%) were assigned to serotype 12. In three farms, 4-complex was the most prevalent serotype, in one farm it was the second most frequently isolated serotype, while serotypes 2 and 1,44, respectively, were the most frequently isolated from the two remaining farms. This serotype distribution differed from the overall country-wide distribution where serotypes 2 and 1,44 are the most prevalent. All serotype 4-complex isolates from the six selected farms were compared by PFGE to serotype 4-complex isolates from the rest of the country. The results showed that there was a high level of diversity among isolates from the whole country, whereas isolates from the six farms were very homogeneous and only displayed one or a few different PFGE patterns on each farm. It is suggested that certain campylobacter clones persist in a confined geographical area, probably at the farm, and that the broiler houses may be repeatedly infected with a few C. jejuni clones during succeeding broiler flocks. New clones may be introduced, however, the sources and vehicles are yet unknown.

Evidence from epidemiological and molecular studies of bovine Escherichia coli O157[ratio ]H7 suggests that strains are frequently transmitted across wide geographic distances. To test this hypothesis, we compared the geographic and genetic distance of a set of international bovine Escherichia coli O157[ratio ]H7 isolates using the Mantel correlation. For a measure of genetic relatedness, pulsed-field gel electrophoresis of six different restriction enzyme digests was used to generate an average Dice similarity coefficient for each isolate pair. Geographic distance was calculated using latitude and longitude data for isolate source locations. The Mantel correlation between genetic similarity and the logarithm of geographic distance in kilometers was −0·21 (P<0·001). The low magnitude of the Mantel correlation indicates that transmission over long distances is common. The occurrence of isolates from different continents on the same cluster of the dendrogram also supports the idea that Escherichia coli O157[ratio ]H7 strains can be transferred with considerable frequency over global distances.

The study investigated the transfer and the stability of the S. intermedius flora in three bitches and their puppies. A total of 240 cutaneous and mucosal isolates of S. intermedius was collected from three healthy Cavalier King Charles spaniels and their puppies during the immediate prepartum period and after whelping, over a total of 15 weeks. The isolates were genotyped with random amplified polymeric DNA-polymerase chain reaction analysis (RAPD-PCR) using two primers. Seventeen different genotypes of S. intermedius were identified. One or two of the genotypes were dominant in each of the bitches and their puppies. The rest were isolated only once or twice from the bitches or their puppies. The study indicates that S. intermedius flora within each studied bitch mainly consisted of one or two dominating and persistent clones, which were transferred from the dam to her puppies immediately after birth.

Pulsed field gel electrophoresis (PFGE) and random amplified polymorphic DNA (RAPD) methods were applied for molecular typing of 130 Mannheimia (Pasteurella) haemolytica serotype A1 isolates obtained from 13 prefectures in Japan. These isolates were divided into 15 ApaI PFGE profiles that formed six distinct clusters (clusters A–F). Fifty-three (40·7%) isolates were classified in cluster B, and 20·0, 13·8, 12·3, 6·9 and 6·1% of isolates were in clusters E, A, F, D and C, respectively. The isolates of cluster B were differentiated into seven subtypes (B1–B7) and subtype B5 contained 63% (34/53) of isolates. RAPD revealed four banding patterns (types I–IV), and among 130 isolates 60·7% (79/130) of isolates were RAPD type I. All of the RAPD type I isolates were grouped into clusters A–C by PFGE. There was no relationship between molecular typing and geographic origin of these isolates. These results indicate that isolates of M. haemolytica A1 strain with various molecular profiles have already spread in Japan and may have caused sporadic infections.

Two forms of Corynebacterium pseudotuberculosis infection in Israeli dairy cattle herds during a survey period of 13 years (1989–2001) are described. The more common form, which was diagnosed in 45 herds, was characterized by ulcerative granulomatous lesions which occurred either sporadically – in 26 herds (with a morbidity rate of up to 5% – or in an epidemic course in 19 herds. Most (80·6%) of the affected animals were cows; the rest were first-calving cows (16·2%) and heifers (3·2%). The morbidity occurred mostly during the summer months. The ulcerative granulomatous lesions appeared in three clinical forms: cutaneous, mastitic and visceral. Mixed forms were also observed. The morbidity rate was 6·4% and the culling rate reached 16·3% of the affected animals. Most of the strains of C. pseudotuberculosis which were isolated from the abscesses in the cutaneous form of the disease and from milk samples failed to reduce nitrate. A decrease in milk production (6%) and an increase in bulk-milk somatic cell count were noted. Necrotic and ulcerative dermatitis on the heel of the foot occurred in an epidemic course in heifers in only two herds during the winter months, with morbidity rates of 7·5 and 76·2%, respectively. C. pseudotuberculosis isolates from skin lesions and from the soil did reduce nitrate. Clinical, epizootiological and microbiological aspects of the infection are described.

In simple epidemiological models that describe the interaction between hosts with their parasites, the infection process is commonly assumed to be governed by the law of mass action, i.e. it is assumed that the infection rate depends linearly on the densities of the host and the parasite. The mass-action assumption, however, can be problematic if certain aspects of the host–parasite interaction are very pronounced, such as spatial compartmentalization, host immunity which may protect from infection with low doses, or host heterogeneity with regard to susceptibility to infection. As deviations from a mass-action infection rate have consequences for the dynamics of the host–parasite system, it is important to test for the appropriateness of the mass-action assumption in a given host–parasite system. In this paper, we examine the relationship between the infection rate and the parasite inoculum for the water flee Daphnia magna and its bacterial parasite Pasteuria ramosa. We measured the fraction of infected hosts after exposure to 14 different doses of the parasite. We find that the observed relationship between the fraction of infected hosts and the parasite dose is largely consistent with an infection process governed by the mass-action principle. However, we have evidence for a subtle but significant deviation from a simple mass-action infection model, which can be explained either by some antagonistic effects of the parasite spores during the infection process, or by heterogeneity in the hosts' susceptibility with regard to infection.

Brachyspira (B.) pilosicoli, the causative agent of intestinal spirochaetosis in pigs, is a quite common laboratory finding from faecal samples of weaned and growing pigs in Finland. A better understanding of the epidemiology of B. pilosicoli in and between Finnish pig farms is needed. Altogether 131 B. pilosicoli isolates from 49 Finnish sow herds were studied by pulsed-field gel electrophoresis. MluI was used as a restriction enzyme for all the isolates, and SmaI for 70 isolates. The isolates were divided into 54 different macrorestriction profiles (MRP) by MluI. Most farms had distinct B. pilosicoli genotypes, and common genotypes among herds were rare. B. pilosicoli was re-isolated after 3 years in three herds; the same MRP persisted in each of these herds. A genetic clustering of B. pilosicoli isolates between two major pork production areas was not detected.