J. Paediatr. Child Health (1992) 28, 459-464
The epidemiology of acute epiglottitis in children in Western Australia J. N. HANNA,’ 8.E.WILD2 and P. D. SLY’ Western Australian Research Institute for Child Health, Perth and ’Princess Margaret Hospital for Children, Subiaco, Western Australia, Australia
Abstract A comprehensive case definition was used to study all cases of epiglottitis that occurred in children under 15 years of age in Western Australia during a 5 year period. There was microbiological evidence of Haernophilus influenzae type b infection in 71% of 103 cases of epiglottitis. Seventy-five per cent of cases occurred in children under 5 years of age. In this age group, the estimated annual incidence (13.5 episodes per 100000) was significantly lower than that reported in Victoria (22.7 per 100 000). The case definition of invasive H. influenzae type b disease used for surveillance purposes in Canada was more sensitive than the definitions used in the United States or England and Wales, yet even the Canadian definition could have detected only 65% of the cases of epiglottitis that occurred in Western Australia. A simple and sensitive surveillance system which could be used to monitor the impact of H. influenzae type b immunization in Western Australia is proposed. Key words:
epiglottitis; Haemophilus influenzae; surveillance
Acute epiglottitis is an uncommon and potentially life-threatening infection that can cause sudden upper airways obstruction. Epiglottitis in children nearly always is caused by Haemophilus influenzae type b.’ Although epiglottitis is an important H. influenzae type b infection, its epidemiology is less completely documented than that of H. influenzae type b meningitis. Most studies of epiglottitis are based upon either hospital case-seriesz or populationbased surveys of microbiologically proven cases.3 However, comprehensive case definitions of epiglottitis which included cases that were not microbiologically confirmed were used in recent population-based studies of all invasive H. influenzae type b infections in Victoria4 and Sydney.5 The Victorian study documented almost as many cases of epiglottitis as H. influenzae type b meningitis and the annual incidence of epiglottitis in Victorian children was almost twice that of children in Sydney. The annual incidence of H. influenzae type b meningitis in children under 5 years of age in Western Australia is very similar to that documented in Victoria,6 but the epidemiology of epiglottitis in children in Western Australia has not been studied previously. Vaccines for protection against H. influenzae type b are licensed for use in infancy in the United States’and are likely to be licensed for use in Australia in the near future. As well as having adequate epidemiological information before the implementation of an immunization programme, it is essential that the impact of the programme on the target disease can be
Correspondence: Dr J. Hanna. Public Health Research Medical Officer, Tropical Centre for Disease Control, PO Box 1103, Cairns, Old 4870, Australia. J. N. Hanna, MBChb. MPH. Senior Research Officer. B. E. Wild, MB, ES, FRCPA, Director of Microbiology. P. D. Sly, MD. FRACP. Head of Clinical Sciences. Accepted for publication 13 May 1992.
monitored. This requires the use of a uniform case definition of the infectious disease under consideration, which must be as sensitive as possible in order to determine the true number of cases. The definition should also be specific and should exclude non-cases (i.e. false positives)! Several differing case definitions of invasive H. influenzae type b disease are being used for surveillance purposes overseasgIl0 The objectives of the current study were: (i) to determine the epidemiology of epiglottitis in children under 15 years of age in Western Australia; (ii)to make comparisons with the epidemiology of the disease documented in Victoria; (iii) to determine the percentage of cases of epiglottitis that might have been detected using various case definitions for the surveillance of invasive H. influenzae type b disease and; (iv) to propose a suitable surveillance system for Western Australia.
METHODS Case definition Only those episodes of epiglottitis in children under 15 years old were included in the study. A child was considered to have epiglottitis if he/she was acutely unwell, there were symptoms and signs suggestive of epiglottitis (e.g. fever, anxiety, dysphagia, drooling, stridor and little or no cough’) and there was evidence of either an acutely inflamed epiglottis or a concomitant H. influenzae type b infection. It was considered that there was evidence of an acutely inflamed epiglottis if there was written documentation of erythema (usually with some degree of oedema) of the epiglottis seen upon laryngoscopy or if a radiologist reported abnormalities consistent with the diagnosis of epiglottitis on a lateral neck X-ray. It was considered that there was evidence of H. influenzae type b infection if there was a positive blood culture or if the organism was cultured from an
J. N. Hanna eta/.
460
endotracheal aspirate or from a swab of the epiglottis, or if a latex particle agglutination test detected H. influenzae type b antigen in a blood sample or in an endotracheal aspirate.’’
Case ascertainment Three different sources of information were used to identify, retrospectively, all episodes of epiglottitis in children under 15 years of age that occurred in Western Australia from 1984 to 1988, inclusive. (1) A computer search was made of hospital morbidity data kept by the Health Department of Western Australia, using the International Classification of Diseases, ninth revision (lCD9),’* code for acute epiglottitis. The codes for three ‘other’ conditions (i.e. acute laryngitis, acute tracheitis and acute laryngitis) that could have included misdiagnosed cases of epiglottitis were also used: for logistic reasons the code for croup was not used. (2) A similar computer search was made of mortality data obtained from the Registrar General of Western Australia. (3) A review of the records of all blood culture examinations performed during the study period by the Department of Microbiology at Princess Margaret Hospital for Children was undertaken. Princess Margaret Hospital, in Perth. is the only specialist paediatric hospital in Western Australia.
I
Data collection Hospital records of all the identified children were examined to determine whether the episode of illness was consistent with the case definition of epiglottitis. Any potentially ambiguous case record was reviewed by a paediatric respiratory physician (PDS), who made a decision as to whether or not the child had epiglottitis. Additional information obtained from the hospital records of each child was the sex, age (to the nearest halfmonth), postcode of residence, race (either ‘Aboriginal’ or ‘nonAboriginal) and the evidence for making the diagnosis of epiglottitis. The details of the children who died, including post-mortem reports, were obtained from the Perth Coroner.
Analyses To calculate incidence rates, population denominator data from the 1986 National Census (Australian Bureau of Statistics) were used. The total study population was 340 117 children under 15 years of age, of whom 96% (325196) were non-Aboriginal. Confidence intervals (CI) of the incidence rates were calculated using the tables of Bailar and Ederer.13 To determine whether there were regional differences in the incidence of epiglottitis each case was assigned to one of three regions based upon residential statistical division (Fig. 1). The temperate south-west region (consisting of the Perth, South-West, Lower and Upper Great Southern and Midlands statistical divisions) includes about 87% of the under-15 nonAboriginal population of Western Australia, whereas the tropical monsoonal Kimberley region (the same as the Kimberley statistical division) includes about 1Yo of the population. The remaining semi-arid region (consisting of the South-eastern, Central and Pilbara statistical divisions) includes about 12% of the abovementioned population (Australian Bureau of Statistics). Differences between incidence rates in the different regions (and
Fig. 1 Map of Western Australia showing the regions as defined for the purposes of the study. The 500 rnm annual average rainfall isohyet is also shown.
between age distribution of cases in Victoria and Western Australia) were tested with the Chi-squared test with Yates’ c~rrection.’~ Because the ages were not normally distributed, the difference between the mean ages of the children who were and were not intubated was tested with the t-test after taking logarithms of the original v a ~ u e s . ’ ~ The percentage of cases of epiglottitis occurring in Western Australia that could have been detected using case definitions used for surveillance purposes in the United States? Canada’’ and England and Wales (N. Begg. PHLS Communicable Disease Surveillance Centre, pers. comm.) were calculated.
RESULTS One hundred and three cases of epiglottitis occurred in children under 15 years of age in Western Australia during the 5 year study period. Ninety (87.5%) of the cases were either admitted directly or referred to the Princess Margaret Hospital for Children. No cases were detected in the case records of all 167 children with ‘other’ discharge diagnoses (i.e. those that could have been confused with epiglottitis). However, 35 of the 138 children with a discharge diagnosis of ‘acute epiglottitis’ were excluded from the study because they did not fulfil the study case definition. Therefore, for the purposes of the study, the
Epidemiology of acute epiglottitis
461
sensitivity of the ICD9 code for acute epiglottitis (464.3) was 100% and the specificity was 83%. Upon review of the clinical notes the paediatric respiratory physician considered that the majority of the 35 excluded children had signs and symptoms consistent with a diagnosis of either croup or other upper respiratory tract infections rather than with acute epiglottitis. Ninety-six (96%) of the 103 cases had evidence of an acutely inflamed epiglottis and 73 (71%) had evidence of H. influenzae type b infection (Table 1).
Clinical details Blood cultures were taken from 86 (83.5%) of the children. Sixty (70%) of the blood cultures were positive, 59 yielding H. influenzae type b on culture. The exception was a group A streptococcus isolated from both blood and endotracheal aspirate of a child 8.5 months old who had a ‘red, swollen epiglottis’ noted at laryngoscopy prior to intubation. The majority (76%) of the children with negative blood cultures had been given antibiotics before blood cultures were collected. Thirteen children, all of whom had symptoms and signs suggestive of epiglottitis, had lateral neck X-ray changes that were consistent with the diagnosis. Five of the 13 had other evidence of epiglottitis such as acute inflammation of the epiglottis noted at laryngoscopy. An artificial airway was established with endotracheal intubation in 77 children and via a tracheostomy in one other child; therefore, 24 (23.5%) of the children were managed conservatively, without intubation. The mean age of the intubated children (31.5 months; median 29.5; range 5-114.5 months) was significantly lower (P0.05) from that occurring in the other two regions combined (5.3 episodes per 100000 children under 15 years of age). The mean age of onset of epiglottitis was 45 months (median, 34.5 months; range, 5-147.5 months). Three-quarters of the cases occurred in children under 5 years of age, and nearly one-third occurred between 24 and 35 months of age. The cumulative age distribution of the cases of epiglottitis in children under 5 years of age in Western Australia is compared with that reported from Victoria in Table 2. Fifty-eight (57%) of the cases of epiglottitis occurred in boys. The male:female ratio was 1.32:l (b0.05).
Table 2 The cumulative age distribution and the annual incidence of H. influenzae type b epiglottitis in Western Australia and Victoria Age (months)
59 7 7 73
Evidence of an acutely inflamed epiglottis visualized changes X-ray changes
Epidemiology
6 1
7 (2) Evidence of H. influenzae type b infection positive blood culture other culture positive antigen detected
(93%)
diagnosis was made at autopsy. The other child (aged 77.5 months), who lived in a remote community, was admitted to a regional hospital in a critical condition and died shortly afterwards. There appeared to be few serious complications in the surviving children and no long term sequelae were noted. Three children had respiratory arrests; despite one child requiring a tracheostomy, all three appeared to have a good outcome. Four of the children were noted to have had convulsions, two ‘febrile’ and two ‘hypoxic’. Six children developed a lower respiratory tract infection, one of whom was hospitalized for 12 days. The mean length of stay in hospital for the 101 surviving children was 3.5 days (median, 3 days; range 1-12 days).
The epidemiology of acute epiglottitis in children in Western Australia J. N. HANNA,’ 8.E.WILD2 and P. D. SLY’ Western Australian Research Institute for Child Health, Perth and ’Princess Margaret Hospital for Children, Subiaco, Western Australia, Australia
Abstract A comprehensive case definition was used to study all cases of epiglottitis that occurred in children under 15 years of age in Western Australia during a 5 year period. There was microbiological evidence of Haernophilus influenzae type b infection in 71% of 103 cases of epiglottitis. Seventy-five per cent of cases occurred in children under 5 years of age. In this age group, the estimated annual incidence (13.5 episodes per 100000) was significantly lower than that reported in Victoria (22.7 per 100 000). The case definition of invasive H. influenzae type b disease used for surveillance purposes in Canada was more sensitive than the definitions used in the United States or England and Wales, yet even the Canadian definition could have detected only 65% of the cases of epiglottitis that occurred in Western Australia. A simple and sensitive surveillance system which could be used to monitor the impact of H. influenzae type b immunization in Western Australia is proposed. Key words:
epiglottitis; Haemophilus influenzae; surveillance
Acute epiglottitis is an uncommon and potentially life-threatening infection that can cause sudden upper airways obstruction. Epiglottitis in children nearly always is caused by Haemophilus influenzae type b.’ Although epiglottitis is an important H. influenzae type b infection, its epidemiology is less completely documented than that of H. influenzae type b meningitis. Most studies of epiglottitis are based upon either hospital case-seriesz or populationbased surveys of microbiologically proven cases.3 However, comprehensive case definitions of epiglottitis which included cases that were not microbiologically confirmed were used in recent population-based studies of all invasive H. influenzae type b infections in Victoria4 and Sydney.5 The Victorian study documented almost as many cases of epiglottitis as H. influenzae type b meningitis and the annual incidence of epiglottitis in Victorian children was almost twice that of children in Sydney. The annual incidence of H. influenzae type b meningitis in children under 5 years of age in Western Australia is very similar to that documented in Victoria,6 but the epidemiology of epiglottitis in children in Western Australia has not been studied previously. Vaccines for protection against H. influenzae type b are licensed for use in infancy in the United States’and are likely to be licensed for use in Australia in the near future. As well as having adequate epidemiological information before the implementation of an immunization programme, it is essential that the impact of the programme on the target disease can be
Correspondence: Dr J. Hanna. Public Health Research Medical Officer, Tropical Centre for Disease Control, PO Box 1103, Cairns, Old 4870, Australia. J. N. Hanna, MBChb. MPH. Senior Research Officer. B. E. Wild, MB, ES, FRCPA, Director of Microbiology. P. D. Sly, MD. FRACP. Head of Clinical Sciences. Accepted for publication 13 May 1992.
monitored. This requires the use of a uniform case definition of the infectious disease under consideration, which must be as sensitive as possible in order to determine the true number of cases. The definition should also be specific and should exclude non-cases (i.e. false positives)! Several differing case definitions of invasive H. influenzae type b disease are being used for surveillance purposes overseasgIl0 The objectives of the current study were: (i) to determine the epidemiology of epiglottitis in children under 15 years of age in Western Australia; (ii)to make comparisons with the epidemiology of the disease documented in Victoria; (iii) to determine the percentage of cases of epiglottitis that might have been detected using various case definitions for the surveillance of invasive H. influenzae type b disease and; (iv) to propose a suitable surveillance system for Western Australia.
METHODS Case definition Only those episodes of epiglottitis in children under 15 years old were included in the study. A child was considered to have epiglottitis if he/she was acutely unwell, there were symptoms and signs suggestive of epiglottitis (e.g. fever, anxiety, dysphagia, drooling, stridor and little or no cough’) and there was evidence of either an acutely inflamed epiglottis or a concomitant H. influenzae type b infection. It was considered that there was evidence of an acutely inflamed epiglottis if there was written documentation of erythema (usually with some degree of oedema) of the epiglottis seen upon laryngoscopy or if a radiologist reported abnormalities consistent with the diagnosis of epiglottitis on a lateral neck X-ray. It was considered that there was evidence of H. influenzae type b infection if there was a positive blood culture or if the organism was cultured from an
J. N. Hanna eta/.
460
endotracheal aspirate or from a swab of the epiglottis, or if a latex particle agglutination test detected H. influenzae type b antigen in a blood sample or in an endotracheal aspirate.’’
Case ascertainment Three different sources of information were used to identify, retrospectively, all episodes of epiglottitis in children under 15 years of age that occurred in Western Australia from 1984 to 1988, inclusive. (1) A computer search was made of hospital morbidity data kept by the Health Department of Western Australia, using the International Classification of Diseases, ninth revision (lCD9),’* code for acute epiglottitis. The codes for three ‘other’ conditions (i.e. acute laryngitis, acute tracheitis and acute laryngitis) that could have included misdiagnosed cases of epiglottitis were also used: for logistic reasons the code for croup was not used. (2) A similar computer search was made of mortality data obtained from the Registrar General of Western Australia. (3) A review of the records of all blood culture examinations performed during the study period by the Department of Microbiology at Princess Margaret Hospital for Children was undertaken. Princess Margaret Hospital, in Perth. is the only specialist paediatric hospital in Western Australia.
I
Data collection Hospital records of all the identified children were examined to determine whether the episode of illness was consistent with the case definition of epiglottitis. Any potentially ambiguous case record was reviewed by a paediatric respiratory physician (PDS), who made a decision as to whether or not the child had epiglottitis. Additional information obtained from the hospital records of each child was the sex, age (to the nearest halfmonth), postcode of residence, race (either ‘Aboriginal’ or ‘nonAboriginal) and the evidence for making the diagnosis of epiglottitis. The details of the children who died, including post-mortem reports, were obtained from the Perth Coroner.
Analyses To calculate incidence rates, population denominator data from the 1986 National Census (Australian Bureau of Statistics) were used. The total study population was 340 117 children under 15 years of age, of whom 96% (325196) were non-Aboriginal. Confidence intervals (CI) of the incidence rates were calculated using the tables of Bailar and Ederer.13 To determine whether there were regional differences in the incidence of epiglottitis each case was assigned to one of three regions based upon residential statistical division (Fig. 1). The temperate south-west region (consisting of the Perth, South-West, Lower and Upper Great Southern and Midlands statistical divisions) includes about 87% of the under-15 nonAboriginal population of Western Australia, whereas the tropical monsoonal Kimberley region (the same as the Kimberley statistical division) includes about 1Yo of the population. The remaining semi-arid region (consisting of the South-eastern, Central and Pilbara statistical divisions) includes about 12% of the abovementioned population (Australian Bureau of Statistics). Differences between incidence rates in the different regions (and
Fig. 1 Map of Western Australia showing the regions as defined for the purposes of the study. The 500 rnm annual average rainfall isohyet is also shown.
between age distribution of cases in Victoria and Western Australia) were tested with the Chi-squared test with Yates’ c~rrection.’~ Because the ages were not normally distributed, the difference between the mean ages of the children who were and were not intubated was tested with the t-test after taking logarithms of the original v a ~ u e s . ’ ~ The percentage of cases of epiglottitis occurring in Western Australia that could have been detected using case definitions used for surveillance purposes in the United States? Canada’’ and England and Wales (N. Begg. PHLS Communicable Disease Surveillance Centre, pers. comm.) were calculated.
RESULTS One hundred and three cases of epiglottitis occurred in children under 15 years of age in Western Australia during the 5 year study period. Ninety (87.5%) of the cases were either admitted directly or referred to the Princess Margaret Hospital for Children. No cases were detected in the case records of all 167 children with ‘other’ discharge diagnoses (i.e. those that could have been confused with epiglottitis). However, 35 of the 138 children with a discharge diagnosis of ‘acute epiglottitis’ were excluded from the study because they did not fulfil the study case definition. Therefore, for the purposes of the study, the
Epidemiology of acute epiglottitis
461
sensitivity of the ICD9 code for acute epiglottitis (464.3) was 100% and the specificity was 83%. Upon review of the clinical notes the paediatric respiratory physician considered that the majority of the 35 excluded children had signs and symptoms consistent with a diagnosis of either croup or other upper respiratory tract infections rather than with acute epiglottitis. Ninety-six (96%) of the 103 cases had evidence of an acutely inflamed epiglottis and 73 (71%) had evidence of H. influenzae type b infection (Table 1).
Clinical details Blood cultures were taken from 86 (83.5%) of the children. Sixty (70%) of the blood cultures were positive, 59 yielding H. influenzae type b on culture. The exception was a group A streptococcus isolated from both blood and endotracheal aspirate of a child 8.5 months old who had a ‘red, swollen epiglottis’ noted at laryngoscopy prior to intubation. The majority (76%) of the children with negative blood cultures had been given antibiotics before blood cultures were collected. Thirteen children, all of whom had symptoms and signs suggestive of epiglottitis, had lateral neck X-ray changes that were consistent with the diagnosis. Five of the 13 had other evidence of epiglottitis such as acute inflammation of the epiglottis noted at laryngoscopy. An artificial airway was established with endotracheal intubation in 77 children and via a tracheostomy in one other child; therefore, 24 (23.5%) of the children were managed conservatively, without intubation. The mean age of the intubated children (31.5 months; median 29.5; range 5-114.5 months) was significantly lower (P0.05) from that occurring in the other two regions combined (5.3 episodes per 100000 children under 15 years of age). The mean age of onset of epiglottitis was 45 months (median, 34.5 months; range, 5-147.5 months). Three-quarters of the cases occurred in children under 5 years of age, and nearly one-third occurred between 24 and 35 months of age. The cumulative age distribution of the cases of epiglottitis in children under 5 years of age in Western Australia is compared with that reported from Victoria in Table 2. Fifty-eight (57%) of the cases of epiglottitis occurred in boys. The male:female ratio was 1.32:l (b0.05).
Table 2 The cumulative age distribution and the annual incidence of H. influenzae type b epiglottitis in Western Australia and Victoria Age (months)
59 7 7 73
Evidence of an acutely inflamed epiglottis visualized changes X-ray changes
Epidemiology
6 1
7 (2) Evidence of H. influenzae type b infection positive blood culture other culture positive antigen detected
(93%)
diagnosis was made at autopsy. The other child (aged 77.5 months), who lived in a remote community, was admitted to a regional hospital in a critical condition and died shortly afterwards. There appeared to be few serious complications in the surviving children and no long term sequelae were noted. Three children had respiratory arrests; despite one child requiring a tracheostomy, all three appeared to have a good outcome. Four of the children were noted to have had convulsions, two ‘febrile’ and two ‘hypoxic’. Six children developed a lower respiratory tract infection, one of whom was hospitalized for 12 days. The mean length of stay in hospital for the 101 surviving children was 3.5 days (median, 3 days; range 1-12 days).
