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Topics in Minority Health Regional Differences in Postneonatal Mortality -- Mississippi, 1980-1983

Mississippi's postneonatal mortality risk is one of the highest among U.S. states. To counter this trend, the Mississippi State Department of Health studied regional differences in postneonatal mortality using linked birth and infant death certificates for 1980-1983.

This certificate linkage provides information on known risk factors for postneonatal mortality that is not routinely collected on death certificates (i.e., maternal age, education, and marital status and infant birthweight and Apgar score). The study was restricted to single-gestation, live-born infants of Mississippi residents, infants who weighed greater than 500 g and less than 8,165 g at birth, and infants who lived beyond the neonatal period (the first 28 days of life). From 1980 through 1983, 876 deaths occurred among these 178,196 postneonates, for a postneonatal mortality risk of 4.9 deaths/1,000 postneonates.

For this 4-year period, the postneonatal mortality risks varied substantially among the nine Mississippi public health districts, from 3.8 postneonatal deaths per 1,000 postneonates in Districts II and IX to 6.8 in District III (Figure 1). Public health districts were chosen as the geographic unit of analysis because of the limited number of postneonatal deaths occurring in many counties, the roughly homogenous composition of the districts, and the fact that most interventions to reduce regional differences would be initiated through these districts. To screen for districts with substantially higher or lower mortality risks than that of the state, investigators used indirect standardization to adjust for race, gender, and birthweight in a method similar to that of Williams (1). After standardization, the risks in Districts I and III, the two northwest districts in the Mississippi Delta region, were significantly higher than the risk for the state, and no district had a significantly lower mortality risk.

A differing mortality pattern was identified by districts when postneonatal mortality risks were examined by race (Figure 1). When the risks of black and other races * were compared with those of whites by districts, the mortality risks for black postneonates ranged from 1.8 to 2.9 times higher. The mortality risks for white postneonates alone varied little, from 2.6 postneonatal deaths/1,000 postneonates in District VII to 3.3 in District I; no district had a white postneonatal mortality risk statistically different from the state's risk. The mortality risks for black postneonates varied from 5.5 in District II to 9.0 and 8.3 in Districts I and III, respectively. By indirect standardization, the risks for black postneonates in Districts I and III were significantly higher than the state's risk for blacks, and no district had a significantly lower risk. Most of the district variations in the postneonatal mortality risks for all races combined occurred because of the wide variation in black postneonatal mortality risks.

To examine the higher mortality risks among black postneonates in Districts I and III, investigators completed a series of district-specific analyses comparing each of these two districts with the other seven districts. Black postneonates in District I had a mortality risk 1.5 times higher than black postneonates in the seven comparison districts (95% confidence limits (CL) = 1.2, 1.9). Adjusting for maternal age, education, marital status, use of prenatal care, and infant birthweight did not substantially alter this comparison.

Further comparisons demonstrated that 1) the higher relative risk for mortality in District I occurred throughout the postneonatal period, and 2) the higher mortality risk was not related to any particular season of the year. However, one important difference was identified. Twenty-four percent of deaths among black postneonates in District I occurred in a hospital or clinic, compared with 44% in other districts (p=0.001). Moreover, roughly 56% of white postneonatal deaths in District I and in other districts occurred in a hospital or clinic.

In relation to the underlying cause of death (Figure 2), black postneonates in District I had a mortality risk difference of 2.8 deaths/1,000 postneonates. Sudden infant death syndrome (SIDS) accounted for 2.0 (71%) of the risk difference; injuries and unknown cause of death accounted for the remainder. However, the confidence in attributing most of this difference to SIDS is weakened because autopsies were performed in only 4% of deaths among black postneonates in District I.

The findings for black postneonates in District III were similar to those in District I except that postneonates with birthweight less than 2,500 g accounted for most of the higher mortality risks. Black postneonates in District III weighing less than 2,500 g, compared with postneonates of the same race and birthweight in the seven comparison districts, had a relative mortality risk of 1.7 (95% CL = 1.3, 2.4), whereas the relative mortality risk for postneonates weighing greater than or equal to2,500 g at birth was only 1.1 (95% CL = 0.86, 1.4). Analyses attempting to explain the higher risk in this lower birthweight group provided little information except that 40% of the deaths among these black postneonates in District III occurred in a hospital compared with 55% for black postneonates in the other seven districts, 67% for white postneonates in District III, and 75% for white postneonates statewide. Reported by: NC Gunter, Div of Public Health Statistics; CE Fox, MD, E Holgren, CNM, Bur of Health Svcs; FE Thompson, MD, State Epidemiologist, Bur of Preventive Health Svcs, Mississippi State Department of Health. Pregnancy Epidemiology Br, Div of Reproductive Health, Center for Health Promotion and Education, CDC. Editorial Note:

This study identified two major disparities in postneonatal mortality risks: 1) statewide, black postneonates had higher risks than white postneonates, and 2) in Districts I and III, black postneonates had higher risks than black postneonates in the seven comparison districts.

The twofold higher mortality risk of black postneonates is an ongoing problem in the United States as well as in Mississippi (2). Mississippi's higher postneonatal mortality rate compared with other states is partly related to a higher percentage of black births in Mississippi. Moreover, the state had the third highest postneonatal mortality rate in the nation for black and other races in 1983 (3).

Beyond the higher overall risk for black compared with white postneonates, the study showed that black postneonates born in Districts I and III had even higher mortality risks than those born in the other seven districts. If the mortality risks for these postneonates could be lowered to those of the other districts, the mortality risk for black postneonates statewide would decrease 10%--a drop greater than that experienced by the state over the last 4 years.

The disparity among health districts went largely unexplained for two reasons. First, information on the underlying cause of death was inadequate. Given the low percentage of autopsies and the completion of many death certificates by non- medically trained coroners, the classification of the cause of death as SIDS or unknown is uninformative. An autopsy is essential in the diagnosis of SIDS to eliminate other likely causes of death. Without it, caution must be used in attributing an increased mortality in Districts I and III to SIDS. Second, although the birth and death certificates include many of the risk indicators for postneonatal mortality, additional medical and social information is not available, such as perinatal morbidity, additional medical history, present illness information, health-care participation, immunization status, financial status, home environment, and parenting skills.

Mississippi has taken direct action to remedy both of these problems, including changing its laws concerning coroners and coroner cases and increasing its number of completed autopsies. Mississippi's physicians and hospitals can also assist in remedying the problem by encouraging autopsies involving both coroner and non- coroner cases and by using autopsy results to more accurately assign the causes of death. More accurate causes of death should help delineate the role of SIDS in the higher black postneonatal mortality in Districts I and III.

In addition, the Mississippi State Department of Health is developing studies to address possible interventions in Districts I and III. These two districts include counties with some of the highest levels of poverty in the country. Although adjustment for maternal education only slightly reduced the RR for mortality, better measures of socioeconomic status might reflect the findings of prior studies that the higher mortality experienced by poor families is primarily mediated through poorer access to or utilization of medical care (4,5). This study's finding of the lack of hospitalization at the time of death suggests that access to health-care facilities may be a problem for those families. References

  1. Williams RL, Cunningham GC, Norris FD, Tashiro M. Monitoring perinatal mortality rates: California, 1970 to 1976. Am J Obstet Gynecol 1980;136:559-68.

  2. CDC. Infant mortality among black Americans. MMWR 1987;36:1-4,9-10.

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