Numerous studies have shown that asthma hospitalization rates are associated with socioeconomic factors, including median household income (at the area level) and lack of insurance (at the individual level). A study of asthma hospitalization rates in California in 1993 (ages 0 to 64) found that areas with median household incomes under $35,000 had hospitalization rates that were 1.5 times higher than areas with higher median incomes. In Boston, in 1992, age and gender standardized hospitalization rates (all ages) were correlated with percentage poverty in an area (r=0.68), percentage holding a bachelor's degree (r=-0.61), and income (r=-0.51). Within New York City in 1994, asthma hospitalization rates were negatively correlated with a zip code area's median household income (r=-0.67), and positively correlated with the percentage of minorities in the population (r=0.82). These findings confirm an earlier study by Billings et al., who reported 6.4-fold variation in asthma hospitalization rates (age 0 to 64) at the zip code level in New York City in 1988, with 70% of this variation explainable by the percentage of households with annual income below $15,000. Millman et al. reported that low-income zip codes had 5.8 times more asthma hospitalizations per capita (age 0 to 64) than high-income zip codes in 11 states in 1988. Using New York State data, Lin et al. showed that hospitalization rates were higher in areas with higher poverty, unemployment, minority populations, and lower education levels. Even in England, 45% of the variation in asthma hospitalization rates across 90 family health services authorities in 1990-95 was attributable to socioeconomic factors, plus the availability of secondary care. To the measure developer's knowledge, only one study has reported partial correlations; it found that in New York City, the percentage of African-American residents (age 0 to 34) was the strongest predictor, and median household income was the next strongest predictor, of asthma hospitalization rates.
The observation that asthma admission rates are higher in areas with low socio-economic status (SES) has led some researchers to hypothesize that lack of access to care, or poor quality outpatient care, may lead to higher admission rates. Although analyses of the National Health and Nutrition Examination Survey found that Medicaid enrollment and Spanish language preference were associated with inadequate asthma therapy, these deficiencies in care were not directly linked to hospitalizations in children. Studies from other settings have shown that African-American asthmatics tend to have fewer scheduled primary care visits, and more hospitalizations and emergency room visits, than White asthmatics. African-Americans' use of asthma medications in children may also be less consistent with current practice guidelines.
Few studies have directly linked high-quality processes of outpatient care with lower hospitalization rates at either the area or the individual level. An in-depth study of asthma treatment practices in New Haven, Boston, and Rochester found that the community with the highest asthma hospitalization rate (Boston) also had lower use of inhaled anti-inflammatory agents and oral steroids. The threshold for admission also appeared to be lower in Boston, as fewer of the admitted children were hypoxemic, relative to the other cities. One case control study from a large health maintenance organization established that not having a written asthma management plan was a strong risk factor for asthma hospitalization in children (after adjusting for severity of asthma), but the use of anti-inflammatory medications was not. More recent studies have confirmed that continuity of care with the same provider and a comprehensive asthma care program decrease the risk of emergency department (ED) visits and hospitalization for asthma. The risk of hospital admission was lower when clinical pathways were used for asthmatic children in emergency rooms of Australian hospitals. In another Australian study, having a written asthma action plan contributed to a reduction in hospital and emergency department attendance.
With patient and parent education, good medical therapy, and outreach programs, adverse outcomes for children can be reduced considerably. For example, Medicaid health maintenance organization (HMO) enrollees had higher age-gender-race adjusted asthma hospital discharge rates than Medicaid recipients enrolled in primary care case management program under fee-for-service reimbursement. On the other hand, experience with Child Health Plus (CHPlus), a health insurance program providing ambulatory and ED coverage for uninsured and low-income children (0 to 13 years) in New York, suggests that some access-improving interventions do NOT reduce asthma hospitalization rates. Visit rates, follow-up visits, and total visits to primary care providers were significantly higher during CHPlus than before enrollment. There was no significant association between CHPlus coverage and ED visits or hospitalizations for asthma, although specialty utilization increased.
