Performance of six birth-weight and estimated-fetal-weight standards for predicting adverse perinatal outcome: a 10-year nationwide population-based study.

OBJECTIVE: To evaluate three birth-weight (BW) standards (Australian population-based, Fenton and INTERGROWTH-21st ) and three estimated-fetal-weight (EFW) standards (Hadlock, INTERGROWTH-21st and WHO) for classifying small-for-gestational age (SGA) and large-for-gestational age (LGA) and predicting adverse perinatal outcomes in preterm and term babies. METHODS: This was a nationwide population-based study conducted on a total of 2.4 million singleton births that occurred from 24 + 0 to 40 + 6 weeks' gestation between 2004 and 2013 in Australia. The performance of the growth charts was evaluated according to SGA and LGA classification, and relative risk (RR) and diagnostic accuracy based on the areas under the receiver-operating-characteristics curves (AUCs) for stillbirth, neonatal death, perinatal death, composite morbidity and a composite of perinatal death and morbidity outcomes. The analysis was stratified according to gestational age at delivery (< 37 + 0 vs ≥ 37 + 0 weeks). RESULTS: Following exclusions, 2 392 782 singleton births were analyzed. There were significant differences in the SGA and LGA classification and risk of adverse outcomes between the six BW and EFW standards evaluated. For the term group, compared with the other standards, the INTERGROWTH-21st BW and EFW standards classified half the number of SGA (< 10th centile) babies (3-4% vs 7-11%) and twice the number of LGA (> 90th centile) babies (24-25% vs 8-15%), resulting in a smaller cohort of term SGA at higher risk of adverse outcome and a larger LGA cohort at lower risk of adverse outcome. For term SGA (< 3rd centile) babies, the RR of perinatal death using the two INTERGROWTH-21st standards was up to 1.5-fold higher than those of the other standards (including the WHO-EFW and Hadlock-EFW), while the INTERGROWTH-21st -EFW standard indicated a 12-26% reduced risk of perinatal death for LGA cases across centile thresholds. Conversely, for the preterm group, the WHO-EFW and Hadlock-EFW standards identified a higher SGA classification rate than did the other standards (18-19% vs 10-11%) and a 20-65% increased risk of perinatal death in term LGA babies. All BW and EFW charts had similarly poor performance in predicting adverse outcomes, including the composite outcome (AUC range, 0.49-0.62) for both preterm (AUC range, 0.58-0.62) and term (AUC range, 0.49-0.50) cases and across centiles. Furthermore, specific centile thresholds for identifying adverse outcomes varied markedly by chart between BW and EFW standards. CONCLUSIONS: This study addresses the recurrent problem of identifying fetuses at risk of morbidity and perinatal mortality associated with growth disorders and provides new insights into the applicability of international growth standards. Our findings of marked variation in classification and the similarly poor performance of prescriptive international standards and the other commonly used standards raise questions about whether the prescriptive international standards that were constructed for universal adoption are indeed applicable to a multiethnic population such as that of Australia. Thus, caution is needed when adopting universal standards for clinical and epidemiological use. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Using linked birth, notification, hospital and mortality data to examine false-positive meningococcal disease reporting and adjust disease incidence estimates for children in New South Wales, Australia.

Meningococcal disease is a rare, rapidly progressing condition which may be difficult to diagnose, disproportionally affects children, and has high morbidity and mortality. Accurate incidence estimates are needed to monitor the effectiveness of vaccination and treatment. We used linked notification, hospital, mortality and birth data for all children of an Australian state (2000-2007) to estimate the incidence of meningococcal disease. A total of 595 cases were notified, 684 cases had a hospital diagnosis, and 26 cases died from meningococcal disease. All deaths were notified, but only 68% (466/684) of hospitalized cases. Of non-notified hospitalized cases with more than one clinical admission, most (90%, 103/114) did not have meningococcal disease recorded as their final diagnosis, consistent with initial 'false-positive' hospital meningococcal disease diagnosis. After adjusting for false-positive rates in hospital data, capture-recapture estimation suggested that up to four cases of meningococcal disease may not have been captured in either notification or hospital records. The estimated incidence of meningococcal disease in NSW-born and -resident children aged 0-14 years was 5·1-5·4 cases/100 000 child-years at risk, comparable to international estimates using similar methods, but lower than estimates based on hospital data.

Estimating the burden of pertussis in young children on hospitals and emergency departments: a study using linked routinely collected data.

Potential underestimation of the health system burden of pertussis was investigated by linking administrative datasets including pertussis notifications, hospitalizations and emergency department (ED) presentations for 1 304 876 children aged <15 years in NSW, Australia. From 2005 to 2008, 3006 children had a pertussis notification, 455 were hospitalized and 644 had an ED presentation with a coded diagnosis of pertussis. Linking hospital and ED records with pertussis notifications identified 140 hospitalizations and 735 ED presentations which occurred ± 7 days from notification but did not have a diagnosis of pertussis recorded. These additional events were more likely to have a diagnosis of bronchiolitis, upper respiratory infection and cough compared to all other admissions and presentations. Including these additional events significantly increased the proportion of notified cases that were hospitalized or visited EDs, particularly for those aged 5 to <15 years. Linked administrative data allowed more comprehensive estimation of the health system burden of pertussis.

Change in smoking status during two consecutive pregnancies: a population-based cohort study.

OBJECTIVE: To investigate changes in tobacco smoking in two consecutive pregnancies and factors associated with the change. DESIGN: Population-based cohort study. SETTING: New South Wales, Australia, 2000-10. POPULATION: A total of 183,385 women having first and second singleton pregnancies. METHODS: Descriptive and multivariable logistic regression analyses of perinatal data linked to hospital admission data. MAIN OUTCOME MEASURES: Proportion of women smoking during their first pregnancy who quit by their second, and of women not smoking in their first pregnancy who did smoke during their second. RESULTS: Among 22,761 smokers in the first pregnancy, 33.5% had quit by their second. Among 160,624 non-smokers in their first pregnancy, 3.6% smoked during their second. Women who were aged ≥25 years, were married, born in a non-English speaking country, used private obstetric care, and lived in a socio-economically advantaged area were more likely to quit or less likely to start smoking in the second pregnancy. Smokers who had gestational hypertension (adjusted odds ratio [OR] 1.36, 95% confidence interval [95% CI] 1.23-1.51), a large-for-gestational-age infant (OR 1.66, 95% CI, 1.46-1.89), and a stillbirth (OR 1.44, 95% CI 1.06-1.94) were more likely to quit, whereas smokers whose infant was small-for-gestational-age (OR 0.65, 95% CI 0.60-0.70) or admitted to special care nursery (OR 0.87, 95% CI 0.81-0.94) were less likely to quit. Among non-smokers in the first pregnancy, the risk of smoking in the second pregnancy increased with late antenatal attendance (e.g. ≥26 weeks, OR 1.30, 95% CI 1.14-1.48), gestational diabetes (OR 1.25, 95% CI 1.07-1.45), preterm birth (e.g. spontaneous, OR 1.25, 95% CI 1.10-1.43), caesarean section (e.g. prelabour, OR 1.13, 95% CI 1.01-1.26), and infant small-for-gestational-age (OR 1.37, 95% CI 1.26-1.48) or required special care nursery (OR 1.14, 95% CI 1.06-1.23). Inter-pregnancy interval of ≥3 years was associated with either change in smoking status. CONCLUSIONS: Most smokers continue to smoke in their next pregnancy, even among those who experienced poor outcomes. Intensive interventions should be explored and offered to women at the highest risk.

Prospective cohort study of body mass index and the risk of hospitalisation: findings from 246361 participants in the 45 and Up Study.

OBJECTIVE: To quantify the risk of hospital admission in relation to fine increments in body mass index (BMI). DESIGN, SETTING, AND PARTICIPANTS: Population-based prospective cohort study of 246,361 individuals aged greater than or equal to 45 years, from New South Wales, Australia, recruited from 2006-2009. Self-reported data on BMI and potential confounding/mediating factors were linked to hospital admission and death data. MAIN OUTCOMES: Cox-models were used to estimate the relative risk (RR) of incident all-cause and diagnosis-specific hospital admission (excluding same day) in relation to BMI. RESULTS: There were 61,583 incident hospitalisations over 479,769 person-years (py) of observation. In men, hospitalisation rates were lowest for BMI 20-<25 kg m(-2) (age-standardised rate: 120/1000 py) and in women for BMI 18.5-<25 kg m(-2) (102/1000 py); above these levels, rates increased steadily with increasing BMI; rates were 203 and 183/1000 py, for men and women with BMI 35-50 kg m(-2), respectively. This pattern was observed regardless of baseline health status, smoking status and physical activity levels. After adjustment, the RRs (95% confidence interval) per 1 kg m(-2) increase in BMI from ≥ 20 kg m(-2) were 1.04(1.03-1.04) for men and 1.04(1.04-1.05) for women aged 45-64; corresponding RRs for ages 65-79 were 1.03(1.02-1.03) and 1.03(1.03-1.04); and for ages ≥ 80 years, 1.01(1.00-1.01) and 1.01(1.01-1.02). Hospitalisation risks were elevated for a large range of diagnoses, including a number of circulatory, digestive, musculoskeletal and respiratory diseases, while being protective for just two-fracture and hernia. CONCLUSIONS: Above normal BMI, the RR of hospitalisation increases with even small increases in BMI, less so in the elderly. Even a small downward shift in BMI, among those who are overweight not just those who are obese, could result in a substantial reduction in the risk of hospitalisation.

Examining area-level variation in service organisation and delivery across the breadth of primary healthcare. Usefulness of measures constructed from routine data.

BACKGROUND: Australia has a universal healthcare system, yet organisation and delivery of primary healthcare (PHC) services varies across local areas. Understanding the nature and extent of this variation is essential to improve quality of care and health equity, but this has been hampered by a lack of suitable measures across the breadth of effective PHC systems. Using a suite of measures constructed at the area-level, this study explored their application in assessing area-level variation in PHC organisation and delivery. METHODS: Routinely collected data from New South Wales, Australia were used to construct 13 small area-level measures of PHC service organisation and delivery that best approximated access (availability, affordability, accommodation) comprehensiveness and coordination. Regression analyses and pairwise Pearson's correlations were used to examine variation by area, and by remoteness and area disadvantage. RESULTS: PHC service delivery varied geographically at the small-area level-within cities and more remote locations. Areas in major cities were more accessible (all measures), while in remote areas, services were more comprehensive and coordinated. In disadvantaged areas of major cities, there were fewer GPs (most disadvantaged quintile 0.9[SD 0.1] vs least 1.0[SD 0.2]), services were more affordable (97.4%[1.6] bulk-billed vs 75.7[11.3]), a greater proportion were after-hours (10.3%[3.0] vs 6.2[2.9]) and for chronic disease care (28%[3.4] vs 17.6[8.0]) but fewer for preventive care (50.7%[3.8] had cervical screening vs 62.5[4.9]). Patterns were similar in regional locations, other than disadvantaged areas had less after-hours care (1.3%[0.7] vs 6.1%[3.9]). Measures were positively correlated, except GP supply and affordability in major cities (-0.41, p < .01). IMPLICATIONS: Application of constructed measures revealed inequity in PHC service delivery amenable to policy intervention. Initiatives should consider the maldistribution of GPs not only by remoteness but also by area disadvantage. Avenues for improvement in disadvantaged areas include preventative care across all regions and after-hours care in regional locations.

Identifying young Aboriginal and Torres Strait Islander children in linked administrative data: A comparison of methods.

BACKGROUND: In the ongoing debate on optimum methods for identification of Indigenous people within linked administrative data, few studies have examined the impacts of method on population counts and outcomes in family-based linkage studies of Aboriginal children. OBJECTIVE: To quantify differences between three algorithms in ascertaining Aboriginal and Torres Strait Islander children in linked administrative data. METHODS: Linked administrative health data for children born in Western Australia (WA) from 2000-2013, were used to examine the cohorts identified by three methods: A) the Indigenous Status Flag (ISF, derived by the WA Data Linkage Branch using a multistage-median approach) for the children alone; B) the ISF of the children, their parents and grandparents; and C) Indigenous status of the child, mother or father on either of the child's perinatal records (Midwives or birth registration), to determine differing characteristics of each cohort. RESULTS: Method B established a larger cohort (33,489) than Method C (33,306) and Method A (27,279), with all methods identifying a core group of 26,790 children (80-98%). Compared with children identified by Method A, additional children identified by Methods B or C, were from less-disadvantaged and more urban areas, and had better perinatal outcomes (e.g. lower proportions of small-for-gestational age, 10% vs 16%). Differences in demographics and health outcomes between Methods C and B were minimal. CONCLUSIONS: Demographic and perinatal health characteristics differ by Aboriginal identification method. Using perinatal records or the ISF of parents and grandparents (in addition to the ISF of the child) appear to be more inclusive methods for identifying young Indigenous children in administrative datasets. KEYWORDS: Aboriginal health, identification, data linkage, Indigenous, child, methodology.

Parity: A key measure of confounding in data-linkage studies of outcomes after medically assisted reproduction.

Parity is a potential confounder of the association between medically assisted reproduction (MAR) and health outcomes. This concept paper describes a population-based record linkage study design for selecting MAR-unexposed women matched to the parity of MAR-exposed women, at the time of the first exposure to MAR. Women exposed to MAR were identified from claims for government subsidies for relevant procedures and prescription medicines, linked to perinatal records. Women unexposed to MAR were identified from linked perinatal and death records, matched to exposed women by age, rurality, age of first child (if any) and parity at the date of first MAR. The availability of a longitudinal, whole-of-population dataset ("population spine") based on enrolments in Australia's universal health insurance scheme was a critical design element. The example application examines cancer risk in women after exposure to MAR. Parity is a confounder in this setting because it is associated with MAR and hormone-sensitive cancers.

Probabilistic linkage of national immunisation and state-based health records for a cohort of 1.9 million births to evaluate Australia's childhood immunisation program.

INTRODUCTION: Several countries have developed national immunisation registers, but only the Nordic countries have linked their registers to other health data in order to comprehensively evaluate the `real world' effectiveness of vaccines. Nordic countries can link datasets deterministically using the national person identifier, but most countries, including Australia, don't have such an identifier to enable this type of linkage. OBJECTIVES: To describe the process for assembling a linked study cohort that will enable the conduct of population-based studies related to immunisation and immunisation policy. METHODS: National death and immunisation databases along with state health data (notifications of vaccine preventable diseases, perinatal data, hospital admissions and emergency department presentations) up until December 2013 were probabilistically linked (using demographic details) for children born between 1996 and 2012 in two states: Western Australia and New South Wales (42% of Australia's population, combined). RESULTS: After exclusions there were 1.95 million children in the study cohort (live born children with both a birth and perinatal record which represents 97.5% of all live births in the state perinatal data collections - our source population) and 18.0 million person years of follow up (mean: 9.2 years per child). The characteristics of children in the cohort were generally similar to those only included in state perinatal databases and outcome measures were in keeping with expected figures from unlinked data sources. However, the lack of a dynamic national population register meant immigrants could not be included. CONCLUSIONS: We have been able to develop a similarly comprehensive system to the Nordic countries based on probabilistic linkage methods. Our experience should provide encouragement to other countries with national immunisation registers looking to establish similar systems.

Chronic pain in Australia: a prevalence study.

This study reports chronic pain prevalence in a randomly selected sample of the adult Australian population. Data were collected by Computer-Assisted Telephone Interview (CATI) using randomly generated telephone numbers and a two-stage stratified sample design. Chronic pain was defined as pain experienced every day for three months in the six months prior to interview. There were 17,543 completed interviews (response rate=70.8%). Chronic pain was reported by 17.1% of males and 20.0% of females. For males, prevalence peaked at 27.0% in the 65--69 year age group and for females, prevalence peaked at 31.0% in the oldest age group (80--84 years). Having chronic pain was significantly associated with older age, female gender, lower levels of completed education, and not having private health insurance; it was also strongly associated with receiving a disability benefit (adjusted OR=3.89, P<0.001) or unemployment benefit (adjusted OR=1.99, P<0.001); being unemployed for health reasons (adjusted OR=6.41, P<0.001); having poor self-rated health (adjusted OR=7.24, P<0.001); and high levels of psychological distress (adjusted OR=3.16, P<0.001). Eleven per cent of males and 13.5% of females in the survey reported some degree of interference with daily activities caused by their pain. Prevalence of interference was highest in the 55--59 year age group in both males (17.2%) and females (19.7%). Younger respondents with chronic pain were proportionately most likely to report interference due to pain, affecting 84.3% of females and 75.9% of males aged 20--24 years with chronic pain. Within the subgroup of respondents reporting chronic pain, the presence of interference with daily activities caused by pain was significantly associated with younger age; female gender; and not having private health insurance. There were strong associations between having interfering chronic pain and receiving disability benefits (adjusted OR=3.31, P<0.001) or being unemployed due to health reasons (adjusted OR=7.94, P<0.001, respectively). The results show that chronic pain impacts upon a large proportion of the adult Australian population, including the working age population, and is strongly associated with markers of social disadvantage.

Effect of infection control measures on the frequency of upper respiratory infection in child care: a randomized, controlled trial.

BACKGROUND: Acute upper respiratory infections are common in children who attend child care, and preventing transmission of disease in this setting depends on actions by child care staff. We set out to discover whether transmission of respiratory infections in child care could be reduced by improved infection control procedures. METHODS: We performed a cluster, randomized, controlled trial of an infection control intervention conducted in child care centers in 1 city in Australia. The intervention was training of child care staff about transmission of infection, handwashing, and aseptic nosewiping technique. Implementation of the intervention was recorded by an observer. Illness was measured by parent report in telephone interviews every 2 weeks. RESULTS: There were 311 child-years of surveillance for respiratory symptoms. By multivariable analysis, there was no significant reduction in colds in intervention center children across the full age range. However, a significant reduction in respiratory illness was present in children 24 months of age and younger. When compliance with infection control practices was high, colds in these children were reduced by 17%. CONCLUSIONS: This trial supports the role of direct transmission of colds in young children in child care. The ability of infection control techniques to reduce episodes of colds in children in child care was limited to children 24 months of age and under.

Effect of infection control measures on the frequency of diarrheal episodes in child care: a randomized, controlled trial.

BACKGROUND: Diarrheal infections are common in children who attend child care, and preventing transmission of disease in this setting depends on actions by child care staff. We set out to discover whether transmission of gastrointestinal infections in child care could be reduced by improved infection control procedures. METHODS: We performed a cluster randomized, controlled trial of an infection control intervention conducted in child care centers for 1 city in Australia. The intervention was training of child care staff about transmission of infection and handwashing and focused on both staff and child behavior. Implementation of the intervention was recorded by an observer. Illness was measured by parent report in telephone interviews every 2 weeks. RESULTS: There were 311 child-years of surveillance for diarrheal episodes. The rate of episodes of diarrhea was 1.9 per child-year in intervention centers and 2.7 per child-year in control centers. Multivariable analysis showed that diarrheal episodes were significantly reduced in intervention center children by 50%. However, the impact of the intervention was confined to children over 24 months of age. For those centers in which children's compliance with handwashing was high, diarrheal episodes were reduced by 66%. CONCLUSIONS: This trial supports education about infection control, for staff and children in child care, as a means of reducing transmission of diarrhea. Reduction in episodes of diarrhea in children in child care was limited to children over 24 months of age.

Loglinear models using capture-recapture methods to estimate the size of a measles epidemic.

Cases of measles reported separately by doctors, hospitals, laboratories, and others are treated as separate captures and releases of the population of children aged up to 10 years who have been infected by measles in a recent epidemic. Loglinear models are used to assess the adequacy of fit of various models for capture-recapture and the size of the epidemic in different age groups is estimated.

Watching the Games: public health surveillance for the Sydney 2000 Olympic Games.

STUDY OBJECTIVE: To describe the development of the public health surveillance system for the Sydney 2000 Olympic Games; document its major findings; and discuss the implications for public health surveillance for future events. DESIGN: Planning for the system took almost three years. Its major components included increased surveillance of communicable diseases; presentations to sentinel emergency departments; medical encounters at Olympic venues; cruise ship surveillance; environmental and food safety inspections; surveillance for bioterrorism; and global epidemic intelligence. A daily report integrated data from all sources. SETTING: Sydney, Australia. Surveillance spanned the period 28 August to 4 October 2000. PARTICIPANTS: Residents of Sydney, athletes and officials, Australian and international visitors. MAIN RESULTS: No outbreaks of communicable diseases were detected. There were around 5% more presentations to Sydney emergency departments than in comparable periods in other years. Several incidents detected through surveillance, including injuries caused by broken glass, and a cluster of presentations related to the use of the drug ecstasy, prompted further action. CONCLUSIONS: Key elements in the success of public health surveillance for the Games included its careful planning, its comprehensive coverage of public health issues, and its timely reporting and communication processes. Future systems need to be flexible enough to detect the unexpected.

Epidemiological investigation of equid herpesvirus-4 (EHV-4) excretion assessed by nasal swabs taken from thoroughbred foals.

Equid herpesvirus-4 (EHV-4) was detected in nasal swabs taken from foals using a PCR based test and this information used to study the epidemiology of EHV-4 disease on three Australian Thoroughbred stud farms in NSW in 1992. There was a very high level of agreement (kappa value of 0.84) between the PCR results and virus isolation using cell culture techniques. There was a strong seasonal distribution of EHV-4 shedding. Twenty-five of 26 positive samples were collected in January and March with the remaining positive sample collected in February. Foals with clinical signs of upper respiratory tract infection per se were no more likely to be shedders of EHV-4 (odds ratio [OR] 1.4, 95% confidence limits [CL] 0.5-3.8). However, EHV-4 was more likely to be isolated from foals exhibiting copious serous or mucopurulent nasal discharge than those with no clinical signs (OR 4.6, 95% CL 1.1-19.0 and OR 2.5, 95% CL 0.8-8.0, respectively). The month of the year was more important than weaning or age as a risk factor for excretion of EHV-4. Male foals and those with a history of respiratory disease that had required veterinary treatment were more likely to shed EHV-4.

Parental smoking and respiratory illnesses in Australian children aged 0-4 years: ABS 1989-90 National Health Survey results.

OBJECTIVE: This study investigated the associations between parental smoking and respiratory infections in Australian children aged 0-4 years. METHODS: Data from the ABS 1989-90 National Health Survey were used. The exposure variables examined were maternal, paternal and combined family smoking. Outcome variables were parent-reported chronic or recent asthma, asthma wheeze, bronchitis, influenza, common cold, cough, otitis media and other respiratory conditions. Logistic regression techniques were used to control for confounding by socio-economic status, child's sex, maternal education, place of residence, ethnicity and family size. RESULTS: Of the 4,281 children in the sample, 45% lived in households with one or more current smokers and 29% had a mother who smoked. Maternal (but not paternal) smoking was significantly associated with asthma (OR 1.52, 95% CI 1.19-1.94) and asthma wheeze (OR 1.51, 95% CI 1.26-1.80). No other significant associations were observed. Positive and significant dose response relationships were found between the amount of maternal smoking and both asthma variables. Population attributable risks were calculated and almost 13% of asthma and asthma wheeze in 0-4 year old Australian children in 1989-90 was estimated to be due to maternal smoking. CONCLUSION: Large numbers of Australian children live in households with smokers. This study, like others, has shown an association between maternal smoking and respiratory illnesses in young children. Further strategies are needed to prevent or reduce young children's exposure to environmental tobacco smoke in their homes.

Estimates of smoking and related behaviour in an immigrant Lebanese community: does survey method matter?

OBJECTIVE: To estimate the prevalence of smoking, stage-of-change and GP advice to quit in the Sydney Lebanese community and whether these findings varied by survey method. METHOD: Three methods--telephone interviews using sampling from the electronic White Pages, personal interviews of a household member selected using cluster sampling and a mailed survey using an electoral roll sample--were used in separate surveys of persons born in Lebanon living in three postcode areas of Sydney in 1997. RESULTS: Smoking prevalence was consistent across the three methods, with male smoking averaging 49% and female smoking averaging 29%. About two-thirds of smoking respondents across each of the survey methods had no plans for quitting. CONCLUSIONS: As smoking prevalence did not vary across the three sampling and survey methods used here, the simplest and most inexpensive method (the electronic White Pages and telephone surveying of identifiable ethnic surnames) should be preferred. IMPLICATIONS: Smoking prevalence in the Sydney Lebanese community is determined consistently using a variety of survey methods.

Cost-effectiveness of measles outbreak intervention strategies.

In this study, we compared the likely cost-effectiveness of alternative strategies for controlling a school-based measles outbreak. The analysis involved assessing the expected costs and number of cases in a school-based outbreak of measles, with no intervention and with each of six control strategies. The marginal cost per case prevented ranged from $32.90 when only previously unvaccinated school children were offered vaccination to $6795 when vaccination was extended to the siblings of school children aged 6 to 12 months. This study provided further evidence of the cost-effectiveness of vaccination in outbreak control, and yielded useful information to inform control strategies in the event of a school-based outbreak. Decisions about which groups of children to aim at and whether to conduct school-based clinics will be influenced by local circumstances, particularly the baseline measles vaccination rate and the measles attack rate among infants.

Genetic structure of populations of beta-haemolytic Lancefield group C streptococci from horses and their association with disease.

The genetic structure of beta-haemolytic Lancefield group C streptococci isolated from horses in Australia was examined by multilocus enzyme electrophoresis. The 249 isolates comprised 70 classified phenotypically as Streptococcus equi subspecies equi, 177 classified as S equi subspecies zooepidemicus and two which were unclassifiable. Forty-one electrophoretic types were identified which could be classified into three major clusters, A, B and C. Of the isolates, 178 fell into cluster B (types 4 to 22) and lay within a genetic distance of 0.36. Sixty-nine of the 70 S equi subspecies equi isolates fell into type 12, which suggests that they were members of a single clone, and the isolates from abscesses were significantly more likely to belong to type 12 than those from horses with no clinical signs (P < 0.001). There were no other significant associations between electrophoretic types or clusters and the isolation of the organism from particular sites. These data suggested that S zooepidemicus may be the archetypal species from which the clone designated subspecies equi has been derived. If isolates of the subspecies equi from other geographical regions also prove to be members of electrophoretic type 12, this hypothesis would be strengthened.

Strangles in horse studs: incidence, risk factors and effect of vaccination.

A questionnaire survey of 179 horse studs in New South Wales was conducted to estimate the incidence of strangles during 1985 to 1988, to identify risk factors for strangles outbreaks and to assess the effect of strangles vaccination. Forty-nine of the studs (27.4%) had at least one strangles outbreak during this period and 62 studs (34.6%) had at least one case of strangles. The average incidence of strangles was 2.1 cases per 100 horses per year. The risk of strangles increased progressively with the total horse population and rose markedly when more than 100 mares had been served in the 1988-89 season. Certain types of feeders, fences and water sources were also significantly associated with outbreaks of strangles. Strangles vaccine was used on 63 studs (35.2%). Thirty-seven of these (58.7%) used the manufacturer's recommended vaccination regime. When other risk factors were taken into account, vaccination had no significant effect on the likelihood of a strangles outbreak.