Popular belief holds that the prevalence of asthma in children is increasing. Does the evidence, however, support this perception? Before this question can be addressed, a definition of asthma is warranted. Although the features of asthma are well documented (Beasley, Crane, Lai, & Pearce, 2000; Gergen, Mullally, & Evans, 1988; Martinez, 2002; Martinez et al., 1995), defining asthma remains a problem (Castro-Rodriguez, Holberg, Martinez, & Wright, 2000; Taylor & Newacheck, 1992). Asthma is characterized by inflammation of the airways linked to hyper-responsiveness (Nowak et al., 1996), meaning that the airways leading to the lungs can narrow when individuals are exposed to anything to which they are sensitive. Inflammation and bronchial constriction are characterized by wheezing, coughing, and chest tightness (Belanger et al., 2003). Scientists and clinicians have agreed that asthma is not a single disease; it exists in many forms (Bacharier et al., 2004).
The past decade has been characterized by proliferation of expert practice guidelines (Fuhlbrigge et al., 2002; National Asthma Education and Prevention Program, 1997), all with the goals of disseminating scientific knowledge to the practicing clinician and the widespread implementation of anti-inflammatory therapy to improve asthma outcomes (Adams et al., 2001; Diaz et al., 2000; Halterman, Aligne, Auinger, McBridge, & Szilagyi, 2000). To this extent, much emphasis has been on early diagnosis and longitudinal care of patients with asthma, along with ensuring adherence to the recommended therapies (Stempel, McLaughlin, Stanford, & Fuhlbrigge, 2005). Yet, as exciting as changes have been in asthma research and practice, many controversies abound when considering asthma and asthma-like symptoms in children aged five and younger.
Data on asthma in children younger than five years of age are sparse. Establishing a diagnosis of asthma in young wheezing children can be challenging because the type, severity, and frequency of asthma symptoms vary widely among children and sometimes even with an individual child (Martinez, 2002). Also, not all wheezing or coughing is caused by asthma (Martinez et al., 1995). Asthma in children usually has many causes or triggers that may change as a child ages (Melen, Wickman, Nordvall, van Hage-Hamsten, & Lindfors, 2001). A child's reaction to a trigger may also change with treatment. In children under five years of age, the most common cause of asthma-like symptoms is upper respiratory viral infections such as the common cold (Lemanske et al., 2005).
Diagnostic tools and current treatment recommendations do not address adequately the needs of children age five and under (van Schayck, van Der Heijden, van Den Boom, Tirimanna, & van Herwaarden, 2000). Asthma is often difficult to diagnose in infants, but in older children the disease can be diagnosed based on the child's medical history, symptoms, and physical exam (Castro-Rodriguez et al., 2000). The majority of the asthma estimates contained in most reports are dependent on conjecturing diagnoses and documenting these results in patients' records, with the potential of either underestimates or overestimates of cases (Kuehni, Davis, Brooke, & Silverman, 2001; van Schayck et al., 2000). Surveillance will help determine the true disease burden of asthma in children younger than five years of age. Our study was conducted to gather preliminary data regarding the prevalence of asthma-like symptoms in young children and to explore environmental exposure sources that may be impacting symptoms.
Background and Subject Selection
Our study was approved in accordance with Allegheny County Health Department (ACHD) procedures, with approval granted by the ACHD director rather than an institutional review board. All participants gave written informed consent.
To determine prevalence of asthma in preschool children below the usual age of spirometry (e.g., 5-6 years), subjects for our exploratory case-control study were selected from the Woman, Infants, and Children (WIC) program--a nutrition program that provides food, infant formula, and breastfeeding/nutrition education to income-eligible pregnant, breast-feeding, and bottle-feeding women. The program targets infants, toddlers, and children up to five years of age who meet certain medical or nutritional risk criteria. The WIC program in Allegheny County, Pennsylvania, serves an average of 15,640 individuals per month, with approximately 50% self-identifying as members of a racial/ ethnic minority. To best capture those individuals who would potentially be at greatest risk of reporting asthma-like symptoms, the investigators focused on five WIC program sites. These sites were selected because of their proximity to air monitoring stations and the number of asthma hospitalizations reported by local hospitals. The local health department reported that these geographical areas had potentially poor air quality (Allegheny County Health Department, 2010).
A counter-matched sampling design (Langholz & Goldstein, 2001) was utilized to select subjects for this nested case-control study. The study base consisted of 5% (n = 810) of the individuals served by Allegheny County WIC, who were caregivers of children five years of age and younger at the time of the interview and had completed active follow-up of WIC services. Of this study base, 14.7% (n = 119) refused participation. From those caregivers of children who chose to participate, all children with histories of wheezing episodes or asthma diagnosis before age five were assigned to the case group (n = 279). Matched controls (n = 412) were asthma-free children randomly selected from each of the qualifying target sites, with approximately equal numbers of...