The outbreak that had to happen: Bordetella pertussis in north-west Western Australia in 1999

In late 1999, an outbreak of Bordetella pertussis occurred in a small town in North-West Western Australia. We undertook an investigation to describe the outbreak and to identify strategies to minimise the impact of future pertussis outbreaks in Australia. In November, people with respiratory symptoms were reviewed in an emergency pertussis clinic, which provided antibiotic treatment or prophylaxis. We conducted a school survey to enhance case ascertainment and followed up those attending the clinic by telephone. Fifty-nine cases of confirmed or probable B. pertussis infection were identified from 124 households (482 persons). Ages ranged from 5 months to 67 years, with children aged 9 to 11 years comprising 24 cases (41%). Early missed diagnoses and a school camp in September attended by 2 symptomatic children appeared to facilitate spread of infection, with the outbreak peak occurring in November. From immunisation records, childhood vaccine coverage in this sample was estimated at 96 per cent. All 21 cases of pertussis among the group under 10 years of age were at least partially vaccinated. There was only one laboratory confirmed case in the high-risk, under one-year of age category. Even in highly immunised populations periodic pertussis outbreaks are inevitable reflecting a vaccine efficacy of about 80 per cent and waning immunity with increasing age. Prevention of pertussis outbreaks depends not only on high vaccination coverage among young children but also early diagnosis and management of cases and their contacts. Clinicians should consider pertussis in the differential diagnosis of persistent cough illness in people of all ages--even those previously immunised.     

Outbreaks of pertussis associated with hospitals--Kentucky, Pennsylvania, and Oregon, 2003

Pertussis outbreaks have been reported in various settings, including sports facilities, summer camps, schools, and health-care facilities. Mild and atypical manifestations of pertussis among infected persons and the lack of quick and accurate diagnostic tests can make pertussis outbreaks difficult to recognize and therefore difficult to control. Outbreaks among health-care workers (HCWs) are of special concern because of the risk for transmission to vulnerable patients. This report describes three pertussis outbreaks among HCWs and patients that occurred in hospitals in Kentucky, Pennsylvania, and Oregon in 2003. These outbreaks illustrate the importance of complying with measures to reduce nosocomial infection when evaluating or caring for patients with acute respiratory distress or cough illness of unknown etiology.     

The frequency of a Norwalk-like pattern of illness in outbreaks of acute gastroenteritis.

Records of 642 outbreaks of acute gastroenteritis were reviewed to determine the proportion of outbreaks that were clinically and epidemiologically consistent with Norwalk-like virus infection. Using as our criteria stool cultures negative for bacterial pathogens, mean (or median) duration of illness 12-60 hours, vomiting in greater than or equal to 50 per cent of cases, and, if known, mean (or median) incubation period of 24-48 hours, we found that 23 per cent of waterborne outbreaks, 4 per cent of foodborne outbreaks, and 67 per cent, 60 per cent, and 28 per cent of outbreaks in nursing homes, in summer camps, and on cruise ships, respectively, satisfied the criteria for Norwalk-like pattern. Of 54 outbreaks that satisfied the criteria for Norwalk-like pattern, 14 were investigated for virus etiology. Ten of these (71 per cent) yielded serologic evidence of Norwalk-like virus infection. Norwalk-like viruses are probably an important cause of outbreaks of acute gastroenteritis. Investigation for Norwalk virus antibody in outbreaks that are clinically and epidemiologically consistent with Norwalk-like virus infection is likely to yield diagnostically useful results.     

Mixture model analysis for establishing a diagnostic cut-off point for pertussis antibody levels

Previous studies of pertussis (whooping cough) that have derived diagnostic cut-off points for pertussis antibody levels have assumed a single distribution for antibody levels and have used small sample sizes. In a recent study of 5409 serum samples from the Third National Health and Nutrition Examination Survey (NHANES III), a finite mixture model was developed to examine the distribution of immunoglobulin G (IgG) antibody levels against pertussis toxin (PT), an antigen specific to the Bordetella pertussis bacterium. The mixture model identified three component populations with antibody levels greater than the quantitative assay's lower limit of quantitation (LLQ) and included a point distribution located at or below the LLQ to account for the excess number of antibody values that fell below the LLQ. The mixture model analysis accounted for the NHANES III design. A cut-off point for anti-PT IgG levels was chosen to have a 99 per cent model specificity based on the two overlapping normal distributions assumed for the two component populations with the highest antibody levels. This cut-off point may have a higher diagnostic sensitivity for acute B. pertussis infection than other cut-off points derived by assuming a single distribution for antibody levels.     

Hospital costs of,and factors contributing to,a pertussis epidemic

Pertussis (whooping cough), a vaccine-preventable and highly infectious respiratory tract disease, caused a major epidemic in Australia during 1997, resulting in large numbers of babies and children being hospitalised. This retrospective study was designed to calculate the costs of this epidemic to a 250-bed paediatric teaching hospital in Western Australia (WA) and discuss the factors contributing to the epidemic.In all, 92 babies and children required 115 hospital admissions for pertussis. Thirteen were admitted to the paediatric or neonatal intensive care unit (P/NICU) at a cost of $229,500 and the 113 ward admissions cost $504,500. In addition, the microbiology diagnostic testing was estimated to cost $200,000. Thus, the real cost to the hospital over the 12-month period was $934,000. The majority of the patients were aged between 2 and 6 months, while all those requiring P/NICU admission were less than 6 months old. The younger the patient the greater the length of stay (average 6.6 days). A comparison was made between patient age, incidence of hospital admission, length of stay and P/NICU admission.When the immunisation compliance rate of inpatienls with pertussis was assessed, only 45 per cent of all those aged more than 2 months were up to date with their pertussis immunisation regime and, for 17 per cent, their immunisation status in the medical records was either lacking or poorly written.This study highlighted the need to improve pertussis immunisation compliance by educating both parents and health professionals regarding expected reactions to, and true contraindications for, pertussis vaccination, as well as for health-care professionals to improve immunisation documentation in the hospital's medical records. (AIC Aust Infect Control 1999; 4(1):15-22.)     

Foodborne disease outbreaks in Australia, 1995 to 2000.

Health agencies are increasingly conducting systematic reviews of foodborne disease outbreak investigations to develop strategies to prevent future outbreaks. We surveyed state and territory health departments to summarise the epidemiology of foodborne disease outbreaks in Australia from 1995 to 2000. From 1995 through 2000, 293 outbreaks were identified, with 214 being of foodborne origin. One hundred and seventy-four (81%) had a known aetiology, and accounted for 80 per cent (6,472/8,124) of illnesses. There were 20 deaths attributed to foodborne illness. Of the 214 outbreaks, bacterial disease was responsible for 61 per cent of outbreaks, 64 per cent of cases and 95 per cent of deaths. The most frequent aetiology of outbreaks was Salmonella in 75 (35%) outbreaks, Clostridium perfringens in 30 (14%), ciguatera toxin in 23 (11%), scombrotoxin in 7 (3%) and norovirus in 6 (3%). Salmonellosis was responsible for eight of the 20 (40%) deaths, as was Listeria monocytogenes. Restaurants and commercial caterers were associated with the highest number of outbreak reports and cases. Outbreaks in hospitals and aged care facilities were responsible for 35 per cent of deaths. The most frequently implicated vehicles in the 173 outbreaks with known vehicles were meats 64 (30%), fish 34 (16%), seafood 13 (6%), salad 12 (6%), sandwiches 11 (5%) and eggs 9 (4%). Chicken, the most frequently implicated meat, was associated with 27 (13%) outbreaks. This summary demonstrates the serious nature of foodborne disease and supports the move to risk-based food safety interventions focusing on mass catering and hospital and aged care facilities.     

Two nosocomial pertussis outbreaks and their associated costs - King County, Washington, 2004.

OBJECTIVE: Pertussis outbreaks in healthcare settings result in resource-intensive control activities, but studies have rarely evaluated the associated costs. We describe and estimate costs associated with 2 nosocomial pertussis outbreaks in King County, Washington, during the period from July 25 to September 15, 2004. One outbreak occurred at a 500-bed tertiary care hospital (hospital A), and the other occurred at a 250-bed pediatric hospital (hospital B). METHODS: We estimated the costs of each outbreak from the hospitals' perspective through standardized interviews with hospital staff and review of contact tracing logs. Direct costs included personnel time and laboratory and medication costs, whereas indirect costs were those resulting from hospital staff furloughs. RESULTS: Hospital A incurred direct costs of $195,342 and indirect costs of $68,015; hospital B incurred direct costs of $71,130 and indirect costs of $50,000. Cost differences resulted primarily from higher personnel costs at hospital A ($134,536), compared with hospital B ($21,645). Total cost per pertussis case was $43,893 for hospital A (6 cases) and $30,282 for hospital B (4 cases). Total cost per person exposed to a pertussis patient were $357 for hospital A (738 exposures) and $164 for hospital B (737 exposures). CONCLUSIONS: Nosocomial pertussis outbreaks result in substantial costs to hospitals, even when the number of pertussis cases is low. The cost-effectiveness of strategies to prevent nosocomial pertussis outbreaks, including vaccination of healthcare workers, should be evaluated.     

A population-based survey of immunisation coverage in two-year-old children

Abstract: A cross-sectional, population-based, cluster-sample survey of 187 children was conducted in the Newcastle area to assess the proportion of two-year-old children who were fully immunised, to ascertain whether administration of these vaccines was age-appropriate and to look for factors predicting incomplete immunisation. Parents or guardians were interviewed at their homes and the immunisation status of the children was verified either by the parent-held record or by the immunisation-provider-held record. Levels of full immunisation were 77 per cent at the time of interview and 72 per cent at the second birthday if Haemophilus influenzae type b (Hib) vaccine was excluded. If it was included, the full immunisation level was 51 per cent. Coverage was highest for oral polio vaccine and lowest for Hib vaccine. Twenty-nine per cent of all immunisations were given early, 44 per cent were given on time and 20 per cent were given late. Doses of vaccines due at older ages were more likely to be given late or not at all. Factors predicting incomplete immunisation were: the principal caregiver being aged under 25 years, being born outside Australia, having post-secondary qualifications, being female and having more than one child in the household. Immunisation coverage levels were not high enough to protect against outbreaks of pertussis and measles and cases of Haemophilus influenzae type b. Immunisation providers should aim to increase coverage to protect the population against all vaccine preventable diseases, and aiming at high-risk groups could more effectively do this.     

Haemolytic-uraemic syndrome in Western Australia, 1980 to 1994

Abstract: A retrospective, population-based study of patients hospitalised with the haemolytic-uraemic syndrome in Western Australia from 1980 to 1994 was undertaken to describe the epidemiology of the disease in this state. We identified 41 patients. Episodes were commonest in children under five years of age (63.4 per cent) and were more frequent in females (58.5 per cent) than in males; only one Aboriginal patient was detected. More than 90 per cent of episodes had a gastrointestinal prodrome lasting from one to 22 days; in 47.6 per cent of these episodes patients had bloody diarrhoea. The average hospital stay was 26 days, and 63.4 per cent of patients required dialysis (mean 10 days). More than 20 per cent of patients developed chronic renal failure, 9.7 per cent died, two patients developed hypertension and one child became epileptic; three of the 10 patients over 16 years of age (30 per cent) died. The haemolytic-uraemic syndrome is potentially fatal, affects mostly young children, and is usually preceded by a gastrointestinal illness. Episodes can occur in common-source outbreaks but, with the exceptions of related cases in families, that appears not to have been so in Western Australia since 1980. There is a need for increased awareness of the haemolytic-uraemic syndrome to enhance prospects for earlier detection and better clinical outcomes. Improved public health surveillance is also needed to reduce the risks of the syndrome in the community.     

Enteric disease outbreak reporting, New South Wales, Australia, 2000 to 2005

OBJECTIVE: To review enteric disease outbreaks reported to the NSW Department of Health. METHODS: Data from existing electronic enteric disease outbreak summary databases were used to describe the number and type of outbreaks reported, burden of illness and cause of the outbreaks. RESULTS: Between 2000 and 2005, 998 enteric disease outbreaks were reported (148 foodborne and 850 non-foodborne), affecting 24 260 people and associated with 771 hospitalisations and 21 deaths. Salmonella was confirmed in 28 per cent of foodborne outbreaks, and norovirus in 18 per cent of non-foodborne outbreaks. CONCLUSIONS: Enteric disease outbreaks cause a substantial burden of disease in NSW.     

Infant immunization and family size

BACKGROUND: To investigate whether a delay in infant immunization is associated with the number of older siblings. METHODS: A cohort analysis of cumulative immunization uptake in 616 children aged 1-4 years recruited for a case-control study of atopic dermatitis in Norwich, UK was performed. The main outcome measures were the age of third pertussis and MMR immunizations. Delayed immunization was defined as a pertussis immunization age 6 months or greater, and MMR immunization aged 16 months or greater. RESULTS: Having a larger number of older siblings was associated with a delay in pertussis immunization (6.2 per cent for children with no older siblings versus 23.3 per cent for children with two or more older siblings), but not in MMR immunization. CONCLUSION: Infants with older siblings are at greater risk of pertussis infection from intrafamilial contagion yet are less likely to be immunized on time.     

Validity of the recording of ischaemic heart disease and chronic obstructive pulmonary disease in the Saskatchewan health care datafiles

The internal validity of the recording of information about ischaemic heart disease (IHD) and chronic obstructive pulmonary disease (COPD) in the administrative health care datafiles of the Canadian province of Saskatchewan is investigated. Comparisons between hospital data and medical charts for acute myocardial infarction and chronic airways obstruction patients showed excellent diagnostic agreement: 97 per cent and 94 per cent, respectively. Appropriate physician service claims were identified for 89 per cent of hospitalizations for IHD and COPD and exact concordance between diagnoses in the two datafiles varied between 15 per cent for acute/sub-acute IHD and 80 per cent for asthma; including any physician diagnosis within the same broad category (IHD or COPD) increased concordance to 79–94 per cent for IHD and 64–88 per cent for COPD. Contextual information related to the hospitalizations was clinically and epidemiologically realistic.     

Melanocytic lesions excised from the skin: what percentage are malignant?

Abstract: We estimated the diagnostic skill of clinicians managing melanocytic skin naevi by measuring the percentage of malignant melanomas, premalignant and potentially malignant naevi, in 1896 excised melanocytic lesions submitted to a pathology service over 11 weeks. They comprised 8 per cent. The percentage increased with age: 4 per cent in the under-40s, 17 per cent in those aged 40–59, and 30 per cent in those over 60, (P < 0.001, sex-adjusted). Although the percentage was twice as high in males (11 per cent) as females (6 per cent), after adjustment for age the difference was not significant. Invasive melanomas, 3 per cent of the total, were similar: 1 per cent were from under-40s; 7 per cent from those aged 40–59 years; and 14 per cent from those over 60. They comprised 4 per cent of lesions from males and 2 per cent from females. These trends may indicate poor specificity of clinical diagnosis, notwithstanding other reasons for removal of naevi (cosmetic), particularly among patients under 40, and females.     

Comparative audit between hospitals: the example of appendectomy

How useful are routine, comparative audit systems? To attempt to answer this question, data from a system in North West Thames were used. A common procedure was selected (appendectomy) and data supplied by 17 surgeons between January and June 1990 were analysed. Aspects of the case-mix, clinical management, diagnostic accuracy and patient outcomes for the surgeons were compared. A total of 401 patients had been treated. All aspects of care varied between surgeons: mean age of patients (19-36 years), proportion of female patients (30-75 per cent), mean length of stay (2.1-7.1 days), prophylactic antibiotic use (0-85 per cent), diagnostic accuracy (40-100 per cent) and incidence of wound infections (0-4 per cent). As a result of the small sample sizes (mean number of cases per surgeon was 23.6) few of these differences were statistically significant. In addition, there were some doubts about the accuracy of some of the data. If such methodological difficulties can be overcome, comparative audit systems offer a practical and useful way of uncovering unusual clinical practices and generating hypotheses for evaluative research.     

Health and economic consequences of an outbreak of pertussis among healthcare workers in a hospital in France.

BACKGROUND: Bordetella pertussis is highly contagious, and because immunity wanes after vaccination, it continues to be a cause of cough among adults. OBJECTIVE: To describe the healthcare services used and productivity losses accrued by healthcare workers (HCWs) missing work due to pertussis. METHODS: After 3 pertussis cases were confirmed among HCWs, all hospital employees and patients with a cough were screened between November 2000 and March 2001. Each potential case underwent diagnostic tests and received antibiotics (spiramycin or azithromycin) when appropriate. Symptomatic employees were not allowed to return to work until they received an antibiotic for at least 5 days. Services used (physician visits and calls, antibiotics, diagnostic tests, hospitalization, and treatment provided to their contacts) were combined with cost estimates (in 2002 euros) for these services in France. RESULTS: Ninety-one potential cases were identified (77 HCWs, 12 patients, and 2 family members). Of them, 89% received antibiotics and 22% had at least one contact who was also treated. Approximately half (55%) of the HCWs who were cases missed 5 days of work. Four patients were admitted to the hospital as a result of the infection. The average medical cost was 297 euros per potential case: diagnostic tests accounted for 32% and hospitalization for 31%. Total cost (medical and productivity) was 46,661 euros for 91 cases, 42% from productivity losses. An investigation to identify these potential cases also accrued additional costs. CONCLUSION: Serious adverse health and economic consequences arose from transmission of pertussis among HCWs, their families, and patients.     

Do we need to boost pertussis immunization within the existing UK vaccination schedule?

Pertussis infection is associated with significant morbidity in younger children (<4 years), which can include pneumonia, seizures and encephalopathy. Around one in 250 cases of pertussis in infants under the age of 6 months lead to death or severe brain damage. In the United Kingdom the control of pertussis infection has been based on a three-dose schedule of combined diphtheria, tetanus, whole-cell pertussis vaccine (DTPw) during the first 4 months of life. Coverage rates for primary vaccination are currently at high levels of over 90 per cent and infection rates are relatively low (approximately 1.2 per 100,000). However, there are concerns over the potential under-reporting of pertussis and clear shifts in the age pattern of notified cases are evident, with surveillance data suggesting a possible upward trend in the absolute numbers of infections in those at most risk (i.e. infants <3 months old). The addition of childhood booster dose(s) of pertussis vaccine to the standard schedule has potential clinical benefits and may be cost-effective. Selective adult booster immunization may also have a role to play in controlling the circulation of pertussis.     

Traveler''s diarrhea at sea: two multi-pathogen outbreaks caused by food eaten on shore visits

In 1976 and 1981, two outbreaks of gastrointestinal illness aboard cruise ships occurred within 24 hours following onshore visits to Haiti and Mexico, respectively. Three hundred eighty-six of 600 (64 per cent) and 98 of 260 (38 per cent) passengers became ill following luncheons in Port-au-Prince, Haiti, and Cozumel, Mexico. No increase in illness was observed among those passengers who did not attend the onshore luncheons. In both outbreaks, unrefrigerated seafood dishes served at outdoor buffets were epidemiologically incriminated as the vehicles of transmission. Several species of Vibrion, Salmonella, and toxigenic Escherichia coli were recovered from stool specimens of ill passengers in both outbreaks. In addition, invasive Escherichia coli and Shigella were isolated from stool specimens of ill passengers who ate at the Haitian buffet. Previous investigations of outbreaks of gastrointestinal illness aboard cruise ships have implicated exposures on board as the source and have involved only a single pathogen.     

Yield of routine annual laboratory screening in the institutionalized elderly.

We examined the yield of a battery of 19 screening laboratory tests performed routinely in 70 functionally intact patients, averaging 82.6 years of age and residing at a chronic care facility. The 70 patients underwent 3,903 screening tests (70 admission batteries and 156 batteries at annual intervals). Twenty per cent of the admission test results and 17 per cent of all subsequent annual test results were "abnormal". "New abnormal" results (previously unknown to the responsible physicians) occurred primarily in five of the 19 screening tests; they were found in 13 per cent of all admission screening tests and in 6 per cent of all annual tests. However, many of the "new abnormalities" were only minimally outside the normal range, and only 26 (0.7 per cent) led to further diagnostic evaluation. Of these 26, only four (0.1 per cent of all tests ordered) led to changes in patient management, none of which benefited the patient in an important way.     

The health and economic burden of pertussis in Canada: A microsimulation study

BackgroundDespite excellent vaccine coverage, pertussis persists in Canada, with high incidence during recent outbreaks and non-negligible incidence in non-outbreak years. While Canadian pertussis incidence is well-characterized, the full health and economic impact of pertussis have not been examined in Canada. We estimated age-specific life years (LYs) and quality-adjusted life years (QALYs) lost, and costs due to pertussis in Ontario, Canada, using a model-based approach.MethodsWe developed a microsimulation model to simulate pertussis natural history. Daily probabilities of pertussis complications, hospitalizations, and disease sequelae as well as utilities and costs for health states were literature-derived. A healthcare payer perspective was used with a lifetime time horizon. Model outcomes were compared to those from a model with no pertussis health states. Probabilistic sensitivity analyses were used to generate distributions for estimates. Economic burden was estimated by multiplying case cost estimates by annual age-specific incidence.ResultsOverall, LYs lost per pertussis case was low, with negligible LYs lost in those aged >4 years. Infants (<6 months) had the greatest mean QALY loss per case (0.58), while adults lost only 0.05 QALYs per case. Infants experienced the greatest mean cost per case of $22,768 (95% CI: 21,144–23,406). Case costs generally declined with age, but increased in seniors (aged 65+) with mean cost of $1920 (95% CI: 1800–2033). Based on historic age-specific incidence, pertussis costs the Ontario healthcare system approximately $7.6–$21.5 M annually. In total economic cost estimates with QALYs valued at 1xGDP (3xGDP) per capita, the net impact of pertussis in Ontario was estimated at $21.7–$66.5 M annually ($50.0–$156.3 M). For all of Canada, total economic costs were estimated at $79.6–$241.3 M ($187.5–$580.5 M) annually.ConclusionThe health and economic consequences of pertussis persistence are substantial and highlight the need for improved control strategies.     

Salmonella infections in hospital. A report from the public health laboratory Service Salmonella Subcommittee

From 1968 to 1977 there were reports of 522 hospital outbreaks in England and Wales due to salmonella infection, comprising 32–50 per cent of all general outbreaks of salmonellosis each year. Analysis in more detail of 197 hospital outbreaks from 1974 to 1977 showed more in maternity, children's and geriatric wards than in medical or surgical wards; extensive outbreaks have taken place in hospitals for the mentally ill and mentally handicapped. There were more outbreaks in the warmer weather than during the winter. Thirty-six different serotypes were involved, the commonest being Salmonella typhimurium. There were 42 deaths in which salmonella infection may have been a contributory factor, 2% of all patients and staff known to be infected. The source of infection was recorded in 76 (39%) of the outbreaks; 24 were considered to be food-borne and in 52 transmission was by other routes.Methods to prevent and control salmonella infection in hospital are discussed.