Appendicectomy in Western Australia: profile and trends, 1981-1997

Abstract

Appendicectomy is one of the most common surgical procedures in adults and children.^1-3 Increases in the incidence of appendicitis were reported during the early part of the 20th century, but a decline has been reported since about 1930.^4-6 Significant advances in diagnostic and surgical technology may have influenced treatment options for patients and surgical outcomes.³ Linked hospital discharge data from Oxford (UK), 1970-1986, reported by Primatesta and Goldacre, showed falls in acute appendicitis and the prophylactic and incidental use of appendicectomy, but no decline in conditions that mimic the disease.⁷ The authors raised the concern that appendicectomy without acute appendicitis was much more common in women than men, questioning the appropriateness of the use of the procedure.⁷

Our study used data from the Quality of Surgical Care Project⁸ stored in the WA Health Services Linked Database (WA Linked Database)⁹ to assess trends in appendicectomy in Western Australia (WA) for 1981-1997.

Methods

The WA Linked Database provided hospital morbidity data for all patients who underwent appendicectomy for 1981-1997. Hospital morbidity records with a separation date before 1988 were selected using the ICPM procedure code 5-470,¹⁰ while ICD-9-CM procedure codes 47.0 and 47.1 were used for patients separated in 1988-1997.¹¹ Data for incidental appendicectomy were evaluated only for the period 1988-1997, as there was no specific incidental appendicectomy procedure code before 1988.

To allow comparison with the Oxford study,⁷ patients who underwent appendicectomy were classified into four subgroups based on procedure and diagnosis codes in conjunction with admission status (Box 1).

Western Australia occupies the western third of the Australian continent. It is sparsely populated, except for the southwest corner of the State and some coastal settlements to the north. Seventy-three per cent of the total population of 1.9 million reside in the capital city of Perth. We used postcode data to classify patients as residing in Perth (metropolitan) or non-metropolitan areas, following the Health Zone classification system of the Health Department of Western Australia. We estimated annual rates of appendicectomy procedures per 100 000 person-years (PY) by the direct method,¹² age standardised to the WA population.¹³ Population estimates were obtained from the Australian Bureau of Statistics.¹⁴ Men and women were analysed separately. We analysed descriptive statistics with the statistical program SPSS,¹⁵ and time trends in rates of admission by Poisson regression models using the SAS procedure GENMOD.¹⁶ These models included terms for "locality" (metropolitan/non-metropolitan), "time", "age-group" and "sex", and associated rate ratios are reported. Depending on goodness of fit, "time" was modelled either as a single term for linear trend or categorically. In our modelling, we also assessed whether trend effects differed by sex and/or locality by using appropriate higher-order interaction terms.

Trends in appendicectomy rates, 1981-1997

Of the 59 749 appendicectomies performed in WA in 1981-1997, 33 352 (55.8%) were performed on female patients and 26 397 (44.2%) on males.

There was a marked decline in the rate of appendicectomy during the study period (Box 2). The age-standardised rate declined by 63% (from 386 to 144 per 100 000 PY) in metropolitan females, by 44% (from 393 to 221 per 100 000 PY) in non-metropolitan females, by 41% (from 240 to 142 per 100 000 PY) in metropolitan males and by 21% (from 258 to 204 per 100 000 PY) in non-metropolitan males. The decline was more marked in females than males and was also greater in the metropolitan area. The adjusted rate ratio (RR) in metropolitan females fell by 6.2% per year (RR, 0.938; 95% CI, 0.933-0.943), compared with 3.2% per year (RR, 0.968; 95% CI, 0.959-0.976) in non-metropolitan females. For metropolitan males, the adjusted rate ratio declined by 3.9% per year (RR, 0.961; 95%CI, 0.955-0.967), compared with the 1.6% per year decline (RR, 0.984; 95% CI, 0.976-0.993) in non-metropolitan males.

Trends in admission classification, 1988-1997

Of the 30 934 appendicectomies performed in WA during 1988-1997, 18 961 (61.3%) were acute emergency admissions, 3820 (12.3%) were other emergency admissions, 2192 (7.1%) were incidental procedures and 5961 (19.3%) were recorded as other appendicectomy admissions. The age-sex profiles for each group are presented in Box 3.

Acute emergency admission appendicectomy was more common in males than females (122.2 v 102.9 per 100 000 PY). The highest rates were in males aged 10-14 years (300 per 100 000 PY) and females aged 15-19 years (289 per 100 000 PY). There was an asymptotic decrease in rates of acute emergency appendicectomy after the 20-24-years age group in both sexes. Rates were higher in non-metropolitan areas for males (149 v 111 per 100 000 PY) and females (131 v 93 per 100 000 PY). The difference between metropolitan and non-metropolitan areas remained significant after adjustment for age, sex and year of separation (RR, 1.37; 95% CI, 1.30-1.45). There was a modest increase in the rate ratio of 1.5% per year over time (95% CI, 0.6%-2.4%) for patients in this group, with no difference between metropolitan and non-metropolitan areas in the rate of acute emergency admissions.

Rates of other emergency appendicectomies were higher in females than males (31 v 15 per 100 000 PY). In females, the rates were highest in those aged 15-19 years (108 per 100 000 PY) and declined sharply after the 20-24-years age group. Rates were higher in non-metropolitan areas for both females (44 v 26 per 100 000 PY) and males (21 v 13 per 100 000 PY) and this effect remained after adjustment for age, sex and year of separation (RR, 1.66; 95% CI, 1.53-1.80).

The age-sex profile of incidental appendicectomies showed a very different pattern. The rate of incidental appendicectomy was higher in females than males (20 v 7 per 100 000 PY). The age profiles were also different, with a sharp, bell-shaped pattern of increase and decrease in women between the ages of 15 and 49 years, with the highest rate occurring in women aged 35-39 years (37 per 100 000 PY). Rates were higher in non-metropolitan areas, with this difference considerably more pronounced in females (29 v 17 per 100 000 PY) than in males (8 v 6 per 100 000 PY). There was a marked decline in the rate of incidental appendicectomies over time among females (Box 4), with a significantly more pronounced trend in metropolitan than non-metropolitan areas (P < 0.001).

The primary surgical procedures with which incidental appendicectomies were performed varied by sex. Incidental appendicectomies in females were most frequent during admissions for operations of the uterus (57%) and ovary (24%), and for operations on the intestines (52%), and hernia and abdomen (20%) in males.

Rates of other appendicectomy were higher in females than males (50 v 22 per 100 000 PY). The highest rate occurred in females aged 15-19 years (139 per 100 000 PY). Rates in this group were higher in non-metropolitan areas for both females (55 v 48 per 100 000 PY) and males (26 v 20 per 100 000 PY). This locality effect was significant after adjustment for age, sex and year of separation (RR, 1.19; 95% CI, 1.09-1.29). There was a strong linear decrease in the incidence of other appendicectomies, with the rate ratio declining 14.4% per year (95% CI, 13.2%-15.5%). This rate of decline was significantly greater for males (17.2%) than females (13.1%; P = 0.002).

Changes in recorded diagnosis, 1988-1997

Changes in the diagnostic profiles of appendicectomy records, excluding incidental appendicectomies, are shown in Box 5. There was a 10-fold reduction in the use of the unspecified appendicitis diagnosis code, with an increase in the use of acute appendicitis diagnosis codes.

To assess whether the increased use of acute appendicitis codes was more likely to reflect changes in recording practices rather than in true disease incidence, trends in appendicectomy rates were examined in males aged 10-24 years, as this group predominantly reflected acute emergency admissions. From 1981 to 1997, age-specific rates of appendicectomy in young males declined by 42% (from 692 to 399 per 100 000 PY) in those aged 10-14 years, by 45% (from 629 to 346 per 100 000 PY) in those aged 15-19 years and by 33% (from 373 to 251 per 100 000 PY) in those aged 20-24 years.

The incidence rate of appendicectomy in WA hospitals declined markedly from 1981 to 1997, consistent with trends reported from other industrialised countries.^5,6 The age-sex profiles of the four different classifications of appendicectomy defined in our study were similar to those found in the Oxford Record Linkage Study.⁷ These profiles were unaffected by the different procedure classifications employed, namely ICD-9-CM in our study and the Office of Population Censuses and Surveys Operations Codes in the Oxford study.

Improvements in diagnostic technology during the past decade have resulted in a much greater use of compression ultrasonography, laparoscopic examination and scoring systems to verify acute appendicitis in patients with abdominal pain.^17,18 These technical improvements may have contributed to the decline in appendicectomy and an improvement in coding practice. Further research is warranted here given a recent finding of no significant benefits from ultrasonography compared with clinical diagnosis alone, other than reduced time to operation.¹⁹

Our study found changes in the specificity of coding of recorded diagnoses of appendicitis from 1988 to 1997. In 1988, most diagnoses of appendicitis were recorded using the non-specific code 541.x. By 1997, relatively few diagnoses of appendicitis were assigned this code. There was an increase in the number of diagnoses coded as acute appendicitis either with peritonitis (540.0 or 540.1) or without peritonitis (540.9). This change could be taken to indicate that the incidence of acute appendicitis increased in WA during 1988-1997. However, our data show a fall in the number of appendicectomies in WA since 1981 and a fall among males aged 10-24 years, the group most likely to be admitted with acute appendicitis. A more likely explanation is that there was an improvement over time in the accuracy of coding in WA hospitals.

There is now concern about the continued practice of incidental appendicectomy.²⁰ While the physiological role of the appendix is unclear, it may have surgical potential in reconstructive urology and the management of faecal incontinence. The frequency of emergency (acute and other) appendicectomy peaks in the 15-19-years age group, the frequency of incidental appendicectomy peaks in the 35-39-years age group in women and at around 70 years in men. A retrospective review and meta-analysis of incidental appendicectomy by Snyder and Selanders supported incidental removal of the appendix in young patients (< 35 years), suggested that the patient's clinical condition should determine incidental removal between 35-50 years, and could not justify incidental appendicectomy in patients older than 50 years.²¹ To address the concerns that incidental appendicectomy is unjustified, further comparison of the risk of appendicectomy and the risk of complications (especially adhesion formation) for different age groups is needed.

The decline in incidental appendicectomy has also seen a convergence of appendicectomy trends for males and females, which most likely reflects a change in attitude by surgeons. The rate of incidental appendicectomy was about five times higher in females than males in 1988, but had reduced to twice the magnitude by 1997. There was no indication of a parallel decline in other abdominal procedures to account for the decline in appendicectomy rates, although the increased use of laparoscopic procedures may have contributed to the decline in incidental appendicectomy.

The decline in the incidence of appendicectomy in WA from 1981 to 1997 is consistent with trends in other industrialised countries and most likely reflects a change in attitude to the use of the procedure, coupled with improvements in diagnostic technology. The trend was most notable in young women in the metropolitan area. There was a fivefold decline in incidental appendicectomy in women in both the metropolitan and non-metropolitan areas. Incidental appendicectomy was more common in women in non-metropolitan areas, which raises questions about differences in practice between the metropolitan and non-metropolitan areas. While the decline in the rates of incidental appendicectomy reflects a change in clinical practice, the question still remains whether incidental appendicectomy is justified to prevent future appendicitis, and does the risk of additional problems and complications outweigh the potential benefit.

Acknowledgements

We thank the National Health and Medical Research Council for the funds that supported this study, and Dr John Bass and the Extramural Unit of the Western Australian Health Services Research Linked Database Project for the linkage of patient records. Mr Neil Donnelly was on secondment from the Needs Assessment and Health Outcomes Unit, Central Sydney Area Health Service, Sydney, NSW, Australia.

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Authors' details

Centre for Health Services Research, Department of Public Health, The University of Western Australia, Nedlands, WA.
James B Semmens, MSc, PhD, Research Fellow, Quality of Surgical Care Project.
C D'Arcy J Holman, MB BS, MPH, PhD, Director.

University Department of Surgery, Fremantle Hospital, Fremantle, WA.
David R Fletcher, MB BS, MD, FRACS, Professor.

Reprints will not be available from the authors.
Correspondence: Dr James B Semmens, Quality of Surgical Care Project, Centre for Health Services Research, Department of Public Health, The University of Western Australia, Nedlands, WA, 6907.

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