Canadian Medical Association Journal Home

Table of Contents
Free eCMAJ TOC

Back issues
Supplements
Selected series

eLetters
About this journal
Info for authors

PubMed

On the trail of necrotizing fasciitis in children
CMAJ 2001;164(2):175 [PDF]

See response from: T. Hsieh, et al
Tauyee Hsieh and colleagues are to be commended for their attempt to define the pediatric presentation and outcome of necrotizing fasciitis versus cellulitis, using a case–control study design [Research].1 One major limitation of their study is the paucity of cases of necrotizing fasciitis (8 cases in total), despite a 16-year period for the retrospective analysis. This raises a question about the accuracy of the ICD-9 coding system for identifying cases of necrotizing fasciitis or similar entities. The answer is that it is not particularly accurate. For example, the sensitivity of ICD-9-CM codes appears to be at most 58.3% for laboratory-confirmed pneumococcal pneumoniae and tends to be much lower than that.2 Identification of common occurrences such as adult stroke,3 myocardial infarction,4 childhood accidents5 and reportable communicable diseases6 via ICD-9 and ICD-9-CM codes is often equally poor, especially among pediatricians.7 Furthermore, coding discrepancies are greater with more complex medical cases,8 such as necrotizing fasciitis.9 I do not criticize the authors for this limitation, but feel that it may help explain why so few cases were identified over such a long study period.

I am concerned that the authors did not estimate a study sample size that would have enabled them to address their question(s) with greater study power and precision. Sample size estimation is an important part of any study design, especially in a case–control study that attempts to examine a rare occurrence like pediatric necrotizing fasciitis.10 Accordingly, a colleague and I developed a practical paper to assist clinician-researchers in the difficult task of estimating sample size for such studies.10 As Hsieh and colleagues pointed out, they may have identified a greater number of cases by embarking on a multicentre study, which is often required when rare diseases are studied. It was for this purpose that the Ontario Group A Streptococcal Study Group was formed.9,11 During 1992 and 1993 alone, this group identified 323 cases of invasive group A streptococcal disease in Ontario; the highest rates were among children and elderly people. However, necrotizing fasciitis occurred in only 6% of all patients, highlighting the rarity of this disease and its high rate of associated morbidity and mortality.9

Joel Ray
Associate
Departments of Critical Care and
  Clinical Epidemiology and Biostatistics
McMaster University
Hamilton, Ont.

References

    1.   Hsieh T, Samson LM, Jabbour M, Osmond MH. Necrotizing fasciitis in children in eastern Ontario: a case–control study. CMAJ 2000;163(4):393-6. [MEDLINE]
    2.   Guevara RE, Butler JC, Marston BJ, Plouffe JF, File TM Jr, Breiman RF. Accuracy of ICD-9-CM codes in detecting community-acquired pneumococcal pneumonia for incidence and vaccine efficacy studies. Am J Epidemiol 1999;149:282-9. [MEDLINE]
    3.   Goldstein LB. Accuracy of ICD-9-CM coding for the identification of patients with acute ischemic stroke: effect of modifier codes. Stroke 1998;29:1602-4. [MEDLINE]
    4.   Cox JL, Melady MP, Chen E, Naylor CD. Towards improved coding of acute myocardial infarction in hospital discharge abstracts: a pilot project. Can J Cardiol 1997;13:351-8. [MEDLINE]
    5.   Beattie TF. Accuracy of ICD-9 coding with regard to childhood accidents. Health Bull (Edinb) 1995;53:395-7. [MEDLINE]
    6.   Campos-Outcalt DE. Accuracy of ICD-9-CM codes in identifying reportable communicable diseases. Qual Assur Util Rev 1990;5: 86-9. [MEDLINE]
    7.   Campos-Outcalt D, England R, Porter B. Reporting of communicable diseases by university physicians. Public Health Rep 1991;106:579-83. [MEDLINE]
    8.   MacIntyre CR, Ackland MJ, Chandraraj EJ, Pilla JE. Accuracy of ICD-9-CM codes in hospital morbidity data, Victoria: implications for public health research. Aust N Z J Public Health 1997;21:477-82. [MEDLINE]
    9.   Laupland KB, Davies HD, Low DE, Schwartz B, Green K, McGeer A. Invasive group A streptococcal disease in children and association with varicella-zoster virus infection. Ontario Group A Streptococcal Study Group. Pediatrics 2000;105(5):E60. [MEDLINE]
    10.   Ray J, Vermeulen M. Sample size estimation for the uninitiated and intimidated. A guide for the sorcerer's apprentice. Can Fam Physician 1999;45:1732-9. [MEDLINE]
    11.   Davies HD, McGeer A, Schwartz B, Green K, Cann D, Simor AE, et al. Invasive group A streptococcal infections in Ontario, Canada. Ontario Group A Streptococcal Study Group. N Engl J Med 1996;335:547-54. [MEDLINE]

 

 

Copyright 2001 Canadian Medical Association or its licensors