Incubation period, severity of disease, and infecting dose: evidence from a Salmonella outbreak

The associations between infecting dose, incubation period, and the severity of disease were examined in a large outbreak of Salmonella typhimurium which occurred at a medical conference in Wales in 1986. Persons who had eaten two or more pieces of the chicken vehicle had, on average, shorter geometric mean incubation periods than those who had only eaten one piece: 16.6 hours (95% confidence interval (CI) 13.5-20.5) compared with 20.7 hours (95% CI 19.0-22.6) (t = 1.97, p < 0.05). Incubation period was negatively correlated with the maximum frequency of diarrheal stools (r = -0.46, 95% CI -0.56 to -0.33), the maximum temperature reached (r = -0.34, 95% CI -0.50 to -0.16), the duration of symptoms (r = -0.41, 95% CI -0.53 to -0.26), and the amount of time taken off from work (r = -0.54, 95% CI -0.65 to -0.41). Those with shorter incubation periods were more likely to have been hospitalized. There was no association between chicken consumption and any of the measures of severity. The authors discuss the evidence that incubation period is inversely related to dose, the use of incubation period as a marker for dose, and the role that individual differences in susceptibility play in determining both the incubation period and the outcome.

Meningococcal disease in Wales: clinical features, outcome and public health management

In Wales, in 1988, 119 patients with meningococcal disease were identified, so giving a crude annual incidence of 4.2 patients per 100,000 population. The combined classical clinical features of fever, vomiting, neck stiffness, headache and purpuric rash were identified in only 9% of patients. Fever and vomiting were the commonest symptoms, both being present in 60% of patients. A rash was noted in 77% of patients but neck stiffness in only 39%. Rash was more common in children, headache and photophobia in adults. A total of 13 patients died, the fatality rare increasing with age from 3% in infants to 20% in older teenagers and adults. Only 15% of 75 patients admitted to hospital by general practitioners were known to have received intravenous or intramuscular penicillin before admission as recommended by the Chief Medical Officers of the Health Departments in the U.K. Only 24% of patients received rifampicin to clear nasopharyngeal carriage before or at discharge from hospital. Altogether, 375 household contacts of patients were identified. At least 84% of them received chemoprophylaxis.

An outbreak of hepatitis A: school toilets as a source of transmission

An outbreak of hepatitis A associated with a Middle school involved 23 cases; 17 were pupils attending the Middle school, one was a teacher, one was a relative of a case, and four were from the associated First school, of whom three had siblings in the Middle school. The probable source case was a male pupil infected by a sibling who had contracted hepatitis A while abroad on holiday. A questionnaire survey and salivary IgG and IgM anti-HAV testing of the pupils demonstrated a statistically significant association between infection and the use of a changing room toilet for defecation. An inspection of the school showed that toilets lacked toilet paper, soap and hand towels. Advice was given to pupils, parents and staff on hygiene. Human normal immunoglobulin was administered to susceptible family contacts, pupils and staff at the school. The school outbreak might have been prevented if the source case for the school had been given immunoglobulin when his sibling developed hepatitis A.

A prolonged outbreak of ornithosis in duck processors

In 1985 an outbreak of ornithosis affected 13 of 80 (16%) workers in a duck-processing plant. New employees were three times more likely to become cases than established employees. The highest attack rate was in those on the production line. Following the outbreak, an occupational health scheme was set up to monitor the health of new recruits to the company. Serological evidence of recent infection was demonstrated in 18 of 37 (49%) new employees tested in the first 3 months of employment. Five (14%) also had clinical evidence of ornithosis. Veterinary investigation of the ducks demonstrated a high proportion with asymptomatic chlamydial infection. It is suggested that ornithosis may be more common in duck processors than is currently supposed. Strategies to reduce occupational risks are discussed.

How is the source of food poisoning outbreaks established? The example of three consecutive Salmonella enteritidis PT4 outbreaks linked to eggs

Three consecutive outbreaks of Salmonella enteritidis PT4 occurred in Wales in 1989 in which epidemiological and microbiological investigation established eggs as the likely source although kitchen inspection and food preparation histories suggested other vehicles of infection. This paper examines the contribution of analytical epidemiology in attributing causation, with particular reference to those limitations which are regarded as inherent in epidemiological evidence. Such evidence, implicating eggs in the three outbreaks, fulfilled 6/7 widely accepted criteria for causation; data to assess the seventh were lacking. Collaboration between different agencies and professionals in investigating outbreaks is very important.

Influenza A and meningococcal disease

There are several anecdotal accounts of the association between outbreaks of influenza and meningococcal disease. The exceptional increase in the number of cases of meningococcal infection 2 weeks after an influenza A outbreak in England and Wales during November and December, 1989, provided an opportunity to investigate the relation between the two events. Patients with meningococcal disease in December, 1989, were more likely than age-matched controls to show serological evidence of recent influenza A infection (odds ratio 3.9, 95% Cl 1.2-13.9). The most likely explanation for the association is immune suppression induced by influenza A, though a lowering of mucosal resistance to meningococcal invasion may also be a factor. Public health authorities should be aware of the association and should be prepared to alert medical practitioners and the public to the increased risk of meningococcal disease when influenza A outbreaks occur.

Epidemiology of Haemophilus influenzae type b invasive disease in Wales

OBJECTIVE

To investigate the epidemiology of invasive disease due to Haemophilus influenzae type b, the clones responsible, and the antibiotic resistance of the isolates.

DESIGN

Prospective population based analysis of clinical and epidemiological data collected for Gwynedd during 1980-90 and in the whole of Wales during 1988-90.

SETTING

19 hospitals in Wales; all medical microbiology laboratories in Wales participated.

PATIENTS

82 patients with confirmed invasive infections caused by H influenzae type b in Gwynedd during 1980-90 and 207 in Wales during 1988-90.

MAIN OUTCOME MEASURES

Clinical and epidemiological measures; analysis of the clonal types of the isolates based on the electrophoretic mobilities of 17 metabolic enzymes; and antibiotic resistance.

RESULTS

The annual incidence of H influenzae type b infections in Gwynedd was 3.2 cases/100,000 and in Wales was 2.5 cases/100,000. Most cases occurred in children aged under 5 years, the highest annual incidence being in those aged under 1 (84.6/100,000 and 56.9/100,000 in Wales). The cumulative risk of acquiring H influenzae type b disease by the fifth birthday was one in 456 in Gwynedd and one in 578 in Wales. Fifteen per cent of cases in Gwynedd and 7% of those in Wales occurred in adults. Predominant clinical conditions were meningitis in children and pneumonia in adults. In Gwynedd 2/70 (3%) children and 5/12 (42%) adults died. Long term neurological sequelae occurred in 8% (4/48) of children who survived haemophilus meningitis. Children presenting with infection were usually the youngest members of their family. No secondary household cases were identified. 100 of 128 (78%) strains were of a single clone, electrophoretic type 12.5, and 4/207 (1.9%) isolates from Wales were resistant to both ampicillin and chloramphenicol.

CONCLUSIONS

The annual rate of infection in children aged under 5 in four Welsh counties was 12-44% higher than that previously published for the United Kingdom. The study emphasises the potential value of a vaccine effective in early infancy and provides baseline data to assess its efficacy after its introduction. Alternatives to ampicillin and chloramphenicol should be used as first line, empirical treatment for severe infections that might be caused by H influenzae type b in Wales.

Vaccine efficacy and control measures in pertussis

An outbreak of pertussis in primary school-children in the St David's area of Pembrokeshire provided the opportunity to estimate pertussis vaccine efficacy. The estimate of efficacy was 88% when notified cases were used, but this fell to 68% when all children with bouts of coughing for two or more weeks were included. Notified cases were significantly less likely to have been vaccinated than other cases with similar symptoms. Therefore vaccine efficacy estimates based upon notified cases are likely to be biased. However, even the lower estimates suggest that pertussis immunisation is highly desirable and efforts to improve coverage should be increased.

Bird attack on milk bottles: possible mode of transmission of Campylobacter jejuni to man

A case-control study was carried out to test the hypothesis that the rise in the rate of Campylobacter jejuni infection in the Brigend area of South Wales during May was due to the consumption or handling of milk from bottles that had been attacked by birds. 32 of 36 cases meeting the case definition were interviewed, along with 2 controls per case, matched for age, sex, and area of residence. There were strong associations between campylobacter infection and doorstep delivery of milk bottles, a history of milk bottle attack by birds, milk bottle attack by birds during the week before illness, and consumption of milk from attacked bottles during the week before illness. There was a very strong dose-response relation between frequency of bird attack and illness. Controls with a history of milk bottle attack by birds were more likely than cases to have taken preventive measures against bird attack and consumption of contaminated milk. Although few people witnessed the attacks, the likely culprits are magpies (Pica pica) and jackdaws (Corvus monedula).

Accuracy and precision of radionuclide measurement of CSF oscillation in the spine

A technique for simultaneously measuring pulsation, translation and diffusion of a radioactive tracer in the spinal cerebrospinal fluid (CSF) has been described. To evaluate the accuracy and precision of this method for measuring CSF oscillation in the spine, an apparatus was designed that moved a radioactive source sinusoidally with known amplitude along a line. With list mode acquisition of radioactive emissions, the amplitude of oscillation was measured for a series of peak-to-peak amplitudes ranging from 0.01 mm to 3.8 mm. For oscillations larger than 0.35 mm peak-to-peak, measured values were within 6.1 percent of the expected values. For the spinal CSF, oscillation larger than 0.4 mm should be measured accurately with this technique.

Outbreak of Salmonella food poisoning amongst delegates at a medical conference

An outbreak of Salmonella typhimurium DT9 food poisoning due to contaminated chicken pieces affected at least 196 delegates at a medical conference. Twelve per cent of the cases reported suffering parasthaesiae. Nine reported serious complications of infection which included rectal prolapse and perianal abscess. Antibiotic therapy did not measurably reduce the duration or severity of diarrhoea. Over 1,600 doctor-days were lost to the NHS. Most doctors sought expert infection control advice before returning to work but the advice given differed between hospitals.

An outbreak of paratyphoid fever in the UK associated with a fish-and-chip shop

An outbreak of Salmonella paratyphi B infection in the UK associated with a fish-and-chip shop is reported. The source of infection for the first three cases was believed to be a food handler who was infected overseas 6 years earlier. His wife whose faeces and urine were originally culture negative continued to run the shop but subsequently her faeces became positive on one occasion. She was considered to have been the source of two further cases, and secondary household spread of infection from these two cases resulted in one symptomatic and two asymptomatic infections. A second household contact of the proprietor also became a faecal excretor 2 months later. We recommend that food handlers living in households or in intimate contact with cases or carriers of S. paratyphi B should be put off work until all household contacts cease excreting the organism.

A christening party outbreak of haemorrhagic colitis and haemolytic uraemic syndrome associated with Escherichia coli O 157.H7

A point source outbreak of haemorrhagic colitis due to Escherichia coli O 157.H7 producing verocytotoxin (VT), took place following a christening party in Birmingham in June 1987. Twenty-six people were affected, six were admitted to hospital and one developed haemolytic uraemic syndrome: there were no deaths. VT + E. coli O 157.H7 was isolated from 13 (57%) of 23 faecal specimens from affected people and from 3 (9%) of 33 specimens from asymptomatic people. Free VT was detected in the faeces of one further asymptomatic person. Illness was associated with eating turkey-roll sandwiches (P less than 0.001) suggesting that cold meats might be an important source of infection.

Outbreaks of salmonella infection in hospitals in England and Wales 1978-87

A total of 248 outbreaks of salmonella infection in hospital affecting over 3000 patients and 110 associated deaths were ascertained in England and Wales in 1978-87, compared with 522 outbreaks of salmonella in 1968-77. The largest reduction was found in outbreaks from children's units and maternity units. Fifty seven (24%) outbreaks were considered to be due to foodborne salmonellosis, and 70 (30%) were reported as person to person spread of the infection. The psychiatric hospital was the type of hospital in which foodborne outbreaks most often occurred, but the risk of being affected in an outbreak not due to food seemed to be highest in maternity units. Better control of infection and better surveillance should lead to earlier investigation and control of outbreaks.

Outcome of neonatal necrotising enterocolitis: results of the BAPM/CDSC surveillance study, 1981-84

Neonatologists in 100 special care baby units in the United Kingdom and Ireland collaborated in a four year surveillance study of neonatal necrotising enterocolitis. The average overall annual reporting rate of necrotising enterocolitis for infants in England and Wales was 0.3/1000 live births, but ranged from 9.5/1000 live births in infants weighing less than 1000 g at birth to 0.2/1000 live births in infants weighing 2500 g or more. There were more deaths among girls, infants who weighed less than 1500 g at birth, those whose bleeding was abnormal or who had low peripheral platelet counts, infants with Gram negative bacteraemia, and very low birthweight infants who developed it during the first few days of life. In both boys and girls, and in all birthweight groups, operation was associated with increased mortality.

Measurement of cerebrospinal fluid movement in the spine. An experimental technique

The authors devised a new technique for measuring cerebrospinal fluid movement in the spine. With gated list mode acquisition of radioactive emissions, bulk flow, oscillations, and dispersion of a bolus of isotope can be measured. The accuracy of the technique was measured in a simulation in which fluid oscillated at 71 cycles/minute and displaced at 6.5 cm/minute. With this method, the measured oscillation frequency and amplitude and the rate of translation were within 10% of actual values.

Salmonella enteritidis phage type 4 infection: association with hen's eggs

Epidemiological and microbiological investigation of the four outbreaks of Salmonella enteritidis phage type (PT) 4 that occurred in Wales in 1988 implicated foods containing shell eggs from hens as the vehicle of infection. In a case-control study of sporadic cases there was a significant association between infection and egg consumption in the 3 days before illness. These findings provide data to support the warnings from the Departments of Health in the United Kingdom about risks of infection from eating raw or undercooked hens' eggs.

Role of infected food handler in hotel outbreak of Norwalk-like viral gastroenteritis: implications for control

Investigation of an outbreak of viral (Norwalk-like) gastroenteritis amongst staff (40 cases), resident guests (over 70 cases), and persons attending functions (54 cases) at one hotel over 8 days suggested that the main vehicle of infection was cold foods prepared by a food handler during and after a mild gastrointestinal illness. He was excreting Norwalk-like virus particles 48 hours after the illness. In addition, ill kitchen staff vomited in the kitchen area and may have contaminated surfaces and stored foods. It is recommended that food handlers should be regarded as potentially infectious until at least 48 hours after clinical recovery from viral gastroenteritis. Stored foods that may have been contaminated should be immediately discarded and areas of the work place which may have been affected should be identified and decontaminated.

First recognized community outbreak of haemorrhagic colitis due to verotoxin-producing Escherichia coli O 157.H7 in the UK

The first recognized outbreak of haemorrhagic colitis due to Escherichia coli O 157.H7 in the United Kingdom affected at least 24 persons living in East Anglia over a 2-week period. The illnesses were characterized by severe abdominal pain and bloody diarrhoea of short duration. Eleven patients were admitted to hospital and there was one death. Patients were mainly adult women who had not eaten out of the home in the 2 weeks before onset. Unlike previously reported outbreaks hamburgers were not the vehicle of infection, and a case-control study suggested that handling vegetables, and particularly potatoes, was the important risk factor.

A cluster of three cases of aplastic anaemia in children

During a 2-week period three unrelated children presented with severe aplastic anaemia at a general hospital serving a population of 25,000 children aged 0-15 years. The probability of this occurring by chance alone was 0.00009 (exact probability cluster analysis). Serology for common viral infections including hepatitis A & B and infectious mononucleosis was negative. It was not possible to demonstrate IgM antibodies to human parvovirus (HPV) by radioimmunoprecipitation or HPV virions by DNA hybridization in the patients or any members of their families. Epidemiological investigation failed to demonstrate a common environmental toxin. It did reveal, however, that all three patients had spent time, within the preceding 3 months in a swimming pool and its surrounding area in a region of Cardiff where none of them resided. Pool maintenance was satisfactory and water analysis showed no abnormality. The possibility must remain that the cluster was caused by an undisclosed environmental toxin.