Sudden Infant Death Syndrome -- United States, 1983-1994

Sudden infant death syndrome (SIDS) is "the sudden death of an infant under 1 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" (1). Although SIDS is a diagnosis of exclusion and of unknown etiology, it is the leading cause of postneonatal mortality in the United States, accounting for approximately one-third of all such deaths (2). This report analyzes age-, race-, and region-specific trends for SIDS in the United States during 1983-1994 (the latest year for which final data are available) and indicates that annual rates of SIDS declined more than three times faster during 1990-1994 than during 1983-1989.

Data about deaths attributed to SIDS and data about autopsy rates are from U.S. public-use mortality data tapes compiled by CDC (3) and include infants (aged less than 365 days) who were born to U.S. residents and died from SIDS (listed as the underlying cause of death) (International Classification of Diseases, Ninth Revision {ICD-9}, code 798.0). Death rates were estimated as the number of these deaths divided by the number of live-born infants during the same period; data about live-born infants are from published natality statistics (4). To characterize SIDS trends, annual data were combined so that the rate of SIDS for 1983-1989 could be compared with the rate for 1990-1994; these periods were selected for comparison because of the implementation during the 1990s of efforts that potentially influenced diagnosis and reporting of SIDS (e.g., increased awareness among health-care providers about risk factors for SIDS, revision of the definition of SIDS, and initiation of national SIDS prevention efforts). Race for infants who died from SIDS was determined by the race of each infant, and race for all live-born infants was determined by the race of the mother. Differences are presented only for black and white infants because the mortality data tapes do not provide accurate race data for other racial/ethnic groups. The linked infant birth-death data set provides accurate race data from birth certificates but is available only through 1991. Neonatal deaths are deaths among infants aged less than 28 days, and postneonatal deaths are those among infants aged 28-364 days.

During 1983-1994, SIDS was listed as the underlying cause of death for 61,882 infants (Table_1). During 1983-1990, the rate of SIDS decreased an average of 1.6% per year; during 1990-1994, the rate decreased an average of 5.6% per year.

Most SIDS cases occurred during the postneonatal period; 93.7% and 92.4% of SIDS cases occurred in this age group in 1994 and 1983, respectively. The postneonatal SIDS rate was 13.9% lower during 1990-1994 than during 1983-1989 (112.9 versus 131.1 per 100,000 live-born infants, respectively). Rates for SIDS were highest among infants aged 1-3 months at death (Table_2): in 1994, deaths in this age group accounted for 68.4% of all SIDS cases.

From 1983-1989 through 1990-1994, the SIDS rate for female infants declined 16.5% (from 114.7 to 95.8 per 100,000 live-born infants), and the rate for male infants declined 13.5% (from 166.0 to 143.6). Male infants were 45% and 50% more likely to die from SIDS than female infants during 1983-1989 and 1990-1994, respectively.

From 1983-1989 through 1990-1994, the SIDS rate for black infants decreased 10.4% and the rate for white infants decreased 16.7%. The average annual decline in the rate of SIDS for black infants was 2.1% during 1983-1990 and 4.1% during 1990-1994. For white infants, the decreases for the two periods were 1.4% and 6.3%, respectively. The rate for black infants was 2.0 and 2.2 times that for white infants during 1983-1989 and 1990-1994, respectively.

Decreases in the SIDS rate during the two time periods also varied by region *. Decreases were greater in the West (23.0%) and Northeast (18.7%) than in the Midwest (11.5%) and South (10.2%). During 1983-1989, SIDS rates were 195.2 per 100,000 live-born infants in the Midwest, 166.8 in the West, 135.5 in the South, and 80.7 in the Northeast; during 1990-1994, the respective rates were 172.8, 128.4, 121.7, and 65.7. During 1983-1989, infants in the Midwest were 2.4 times more likely than infants in the Northeast to die from SIDS; during 1990-1994, the ratio was 2.6.

The percentage of deaths attributed to SIDS that were followed by an autopsy increased from 85.8% in 1983 to 93.4% in 1990 and to 95.7% in 1994. The percentage of autopsies were similar by race but differed by region. In 1983, 25.7% of deaths attributed to SIDS in the South were not followed by an autopsy, compared with less than 15% in other regions. By 1994, this percentage had declined to 6.8% in the South and less than 3% in other regions.

Reported by: Div of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion; Div of Vital Statistics, National Center for Health Statistics, CDC.

Editorial Note

Editorial Note: The findings in this report indicate that the decline in the rate of SIDS was greater during 1990-1994 than during 1983-1989. For the first time since 1980, in 1994, SIDS declined from the second to the third leading cause of infant mortality. In addition, preliminary mortality data for 1995 indicate that the SIDS rate declined 18.3% from 1994, representing the largest annual percentage decline since 1983 and suggesting that the higher rate of decline observed during 1990-1994 is continuing (2). This trend may reflect changes in the prevalence of known risk factors and/or changes in the diagnosis of SIDS.

Many of the risk factors for SIDS identified during the 1980s (e.g., low birthweight, young maternal age, and poor socioeconomic status) are not readily amenable to intervention (5). However, a strong association between the infant prone sleeping position and SIDS had been established by 1990 (6). During 1992, the American Academy of Pediatrics began recommending that parents place infants on their back or side to sleep (7), and during 1994, the national "Back to Sleep" campaign (6) began promoting the nonprone sleeping position as well as other modifiable risk factors (e.g., breastfeeding was encouraged and exposure to tobacco smoke and overheating was discouraged). Studies in other countries indicated that SIDS rates declined approximately 50% concurrent with decreases in the prevalence of prone sleeping (6). In the United States during 1992-1995, the SIDS rate declined 30% concurrent with a decrease in the prevalence of prone sleeping from 78% in 1992 to 43% in 1994 (6). Although the prevalence of breastfeeding did not change substantially during the study period (8), birth-certificate data indicate that during 1989-1994, the prevalence of cigarette smoking during pregnancy declined by approximately 25% (from 19.5% to 14.6%) (9).

Race/ethnicity-specific differences in SIDS most likely reflect variations in the prevalence of risk factors for SIDS, including socioeconomic and demographic factors, certain medical conditions (e.g., prematurity), and the quality of and access to health care (5). However, because race/ethnicity-specific prevalences of prone sleeping during the early 1990s are unavailable, the effectiveness of campaigns to discourage the prone sleeping position could not be evaluated by race/ethnicity. Regional differences in SIDS rates may reflect differences in the prevalence of risk factors as well as variations in state protocols for investigating suspected cases of SIDS.

Based on preliminary data, the black/white ratio for SIDS in 1995 (2.4) was higher than during any other year since 1983, indicating that racial/ethnic disparities in SIDS may be increasing. Because of persistent race-specific differences in risks for SIDS, prevention efforts should be targeted especially to black infants. In addition, evaluation efforts should assess whether race-specific and regional differences are related to variations in the prevalence of preventable risk factors, in methods of diagnosis, or in the effectiveness of prevention messages.

Before 1991, only an autopsy was required for the diagnosis of SIDS. During 1991, the official definition of SIDS was revised to require an investigation of the death scene (1), although this change may not have been uniformly implemented by all state/local health departments. However, because the non-SIDS postneonatal mortality rate did not change substantially during 1983-1989 and 1990-1994, a shift in diagnosis probably did not account for the larger declines in SIDS during 1990-1994. The occurrence of related diagnoses such as suffocation (ICD-9 code 913) and other ill-defined conditions (ICD-9 codes 780-797 and 799) increased from 1983-1989 to 1990-1994 (28.8% and 29.2%, respectively) (3), but these diagnoses combined comprise less than 1% of all infant deaths.

The Back to Sleep campaign should continue to publicize risk factors for SIDS and ensure that prevention messages reach all segments of the population, especially those at high risk for SIDS. In addition, widespread implementation of the recently published national guidelines for death scene investigation of sudden, unexplained infant deaths (10) should help standardize the investigation of these deaths and improve the accuracy of SIDS diagnoses.

References

1. 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.

2. NCHS. Births and deaths: United States, 1995. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1996. (Monthly vital statistics report; vol 45, no. 2, suppl).

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, 1983-1994.

4. NCHS. Vital statistics of the United States, 1983-1994. Vol 1. Natality. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1983-1994.

5. Hoffman HJ, Hillman LS. Epidemiology of the sudden infant death syndrome: maternal, neonatal, and postneonatal risk factors. Clin Perinatol 1992;19:717-37.

6. Willinger M. SIDS prevention. Pediatr Ann 1995;24:358-64.

7. Task Force on Infant Positioning and SIDS, American Academy of Pediatrics. Positioning and SIDS. Pediatrics 1992;89:1120-6.

8. NCHS. Healthy people 2000 review, 1994. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1995.

9. NCHS. Advance report of final natality statistics, 1994. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1996. (Monthly vital statistics report; vol 44, no. 11, suppl).

10. CDC. Guidelines for death scene investigation of sudden, unexplained infant deaths: recommendations of the interagency panel on sudden infant death syndrome. MMWR 1996;45(no. RR-10).

Northeast=Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont; Midwest=Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin; South=Alabama, Arkansas, Delaware, District of Columbia, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, and West Virginia; and West=Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming.

TABLE 1. Number of cases of and rate * for sudden infant death syndrome +, by race &
and year -- United States, 1983-1994
==================================================================================================
                 Black            White            Total @
            ---------------   --------------   ---------------
Year          No.     Rate      No.    Rate      No.     Rate
--------------------------------------------------------------
1983-1989   10,349    244.8   25,829   121.2   37,483    141.0

1983         1,518    269.8    3,613   122.6    5,305    145.8
1984         1,439    253.3    3,656   123.2    5,245    142.9
1985         1,357    233.2    3,757   123.7    5,315    141.3
1986         1,451    244.7    3,654   121.0    5,278    140.5
1987         1,447    236.8    3,605   118.4    5,230    137.3
1988         1,520    238.0    3,771   121.6    5,476    140.1
1989         1,617    240.2    3,773   118.2    5,634    139.4

1990-1994    7,315    219.3   16,165   101.0   24,399    120.3

1990         1,578    230.6    3,643   110.7    5,417    130.3
1991         1,589    232.8    3,572   110.2    5,349    130.1
1992         1,471    218.4    3,239   101.2    4,891    120.3
1993         1,442    218.9    3,056    97.0    4,669    116.7
1994         1,235    194.1    2,655    85.1    4,073    103.0
--------------------------------------------------------------
* Per 100,000 live-born infants.
+ International Classification of Diseases, Ninth Revision, code 798.0
& Race for infants who died from SIDS was determined by the race of each infant, and race for
  all live-born infants was determined by the race of the mother. Differences are presented only
  for black and white infants because the mortality data tapes do not provide accurate race data
  for other racial/ethnic groups.
@ Includes infants of all racial/ethnic groups.
==================================================================================================

TABLE 2. Number of cases of and rate * for sudden infant death syndrome +,
by age at death -- United States, 1983-1989 and 1990-1994 &
==========================================================================
                             1983-1989           1990-1994
          Age at death     --------------      --------------
            (months)        No.      Rate       No.      Rate
          ---------------------------------------------------
               <1          2,636      9.9      1,496      7.4
                1          8,953     33.4      5,612     27.7
                2          9,860     37.1      6,591     32.5
                3          6,945     26.1      4,643     22.9
                4          3,885     14.6      2,707     13.3
                5          2,099      7.9      1,346      6.6
                6          1,234      4.6        808      4.0
                7            738      2.8        498      2.5
                8            502      1.9        312      1.5
                9            295      1.1        177      0.9
               10            189      0.7        130      0.6
               11            147      0.6         78      0.4

              Total       37,483    141.0     24,398    120.3
          ---------------------------------------------------
* Per 100,000 live-born infants.
+ International Classification of Diseases, Ninth Revision, code 798.0
& One infant, for whom age was missing, was excluded from this analysis.
==========================================================================

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