Sudden Infant Death Syndrome -- United States, 1980-1988

Sudden infant death syndrome (SIDS) (the abrupt and unexplained death of an apparently healthy infant) is the second leading cause of infant mortality in the United States (1) and the eighth leading cause of years of potential life lost (2). This report analyzes race- and region-specific data for SIDS during 1980-1988.

This analysis examined death certificate data from public-use mortality data tapes compiled by CDC's National Center for Health Statistics (3) and included infants aged less than or equal to 364 days at the time of death from SIDS (International Classification of Diseases, Ninth Revision, code 798.0) who were born to U.S. residents. Neonatal deaths were defined as deaths among infants aged less than 28 days; postneonatal deaths were those among infants aged 28-364 days. Data on live-born infants were obtained from published natality statistics (4) and were used as the denominator for determining mortality rates. Rates of SIDS were calculated by dividing the number of SIDS cases in a year by the number of live-born infants in that calendar year.

From 1980 through 1988, 47,932 infants born to U.S. residents died from SIDS (Table 1). During that time, overall SIDS rates declined 3.5% for white infants and 19.2% for black infants; the decline was significant for black infants (p less than 0.001; chi-square test for trend). In addition, throughout the 9-year period, SIDS rates were higher for black infants than for white infants. However, the black-to-white rate ratio declined from 2.2 in 1980 to 1.8 in 1988 (p less than 0.002); this decline occurred primarily among postneonatal infants.

Of all SIDS cases, 92.4% in 1980 and 93.2% in 1988 were postneonatal deaths. Neonatal SIDS cases represented a relatively small proportion of total SIDS cases: from 1980 through 1988, this proportion declined from 7.2% to 6.5% among whites and from 8.2% to 7.1% among blacks.

Autopsy rates for deaths diagnosed as resulting from SIDS increased from 82.3% in 1980 to 92.5% in 1988; percent increases were similar for both black and white infants. Autopsy rates for neonatal deaths increased from 79.0% in 1980 to 91.6% in 1988.

For white infants, overall SIDS rates for 1980-1988 were highest in the West, followed by the Midwest, the South, and the Northeast. For black infants, in 1980 SIDS rates were highest in the Midwest, followed by the West, Northeast, and South; in 1988, rates were lowest in the Northeast.

Reported by: A Sinha, Harvard Medical School, Cambridge, Massachusetts. Div of Field Epidemiology, Epidemiology Program Office; Div of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note

Editorial Note: In 1990, the National Institute of Child Health and Human Development (NICHD) defined SIDS as "the sudden death of an infant under one year of age which remains unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history" (5). The previous definition of SIDS, adopted at the Second International Conference of Sudden Death in Infants in 1969, did not require death scene examination (6).

The NICHD definition of SIDS emphasizes the importance of autopsies and death scene investigations in ruling out other causes of death before a SIDS diagnosis is assigned. The increased autopsy rates among reported SIDS cases during 1980-1988 indicates the availability of more complete data for diagnostic purposes. However, in this analysis, to what extent autopsy data were used in the classification of cause of death could not be determined.

Throughout 1980-1988, the risk for SIDS was higher for black infants than white infants, although the differences in risk narrowed somewhat during the period. However, the larger decline in SIDS rates for black infants cannot be explained by changes in autopsy rates, which were similar for both races in 1980 and increased equally during the period.

The consistent regional variations in SIDS rates during the study period remain unexplained. A recent report from Denmark ascribed such differences in SIDS rates to varying postmortem protocols and interpretation of history and autopsy information (7).

Although many risk factors have been associated with SIDS (8) -- including the possible role of prone sleeping position (9,10) -- neither a specific etiology nor a pathophysiology has been delineated. The diagnosis thus remains one of exclusion. The complexity of this syndrome is illustrated by the varying risks for SIDS among geographically and racially defined infant populations. A greater understanding of the etiologic mechanisms of SIDS and an evaluation of cause-of-death assignment by geographic area may identify factors that affect the mortality rates found in this analysis.

References

1. CDC. Infant mortality -- United States, 1989. MMWR 1992;41:81-5.

2. CDC. Years of potential life lost before ages 65 and 85 -- United States, 1989-1990. MMWR 1992;41:313-5.

3. NCHS. Vital statistics mortality data, multiple cause-of-death detail (machine-readable public-use data tapes). Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1980-1988.

4. NCHS. Vital statistics of the United States -- 1980-1988 (annual). Vol 1. Natality. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC.

5. Willinger M, James LS, Catz C. Defining the sudden infant death syndrome (SIDS): deliberations of an expert panel convened by the National Institute of Child Health and Human Development. Pediatr Pathol 1991;11:677-84.

6. Beckwith JB. Discussion of terminology and definition of sudden infant death syndrome. In: Bergman AB, Beckwith JB, Ray CG, eds. Proceedings of the Second International Conference on Causes of Sudden Death in Infants. Seattle: University of Washington Press, 1970.

7. Helweg-Larson K, Knudsen LB, Gregersen M, Simonsen J. Sudden infant death syndrome (SIDS) in Denmark: evaluation of increasing incidence of registered SIDS in the period 1972 to 1983 and results of a prospective study in 1987 through 1988. Pediatr 1992;89:855-9.

8. Haglund B, Cnattingius S. Cigarette smoking as a risk factor for sudden infant death syndrome: a population based study. Am J Public Health 1990;80:29-32.

9. Hunt CE, Shannon DC. Sudden infant death syndrome and sleeping position. Pediatrics 1992;90:115-8.

10. Dwyer T, Ponsonby A-LB, Newman NM, Gibbons LE. Prospective cohort study of prone sleeping position and sudden infant death syndrome. Lancet 1991;337:1244-7.

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