Acute lower respiratory infections (ALRI) are the single most important cause of death of children under 5 years, responsible annually for approximately 20% of the 10 million under-5 deaths globally. (1,2) Prevention strategies are required urgently, including control of risk factors. A growing body of evidence links household indoor air pollution from solid fuels with ALRI in developing countries: recent estimates suggest this may be responsible for nearly one million child ALRI deaths. (3) However, these figures are based on relatively few observational studies with considerable variation in ALRI case-finding methods, indirect exposure assessment using proxies such as fuel type) and risk of residual confounding. (4) To address these limitations we conducted a community-based randomized controlled trial with improved chimney stoves in rural Guatemala.
Weaknesses in previous ALRI field studies, and the methodological issues common to trials of environmental interventions, highlighted three particular challenges for this study:
1. To ensure that few cases are missed. Frequent home visits by staff trained to recognize signs such as fast breathing can achieve high sensitivity for ALRI. (5) It has been suggested that early treatment associated with more frequent visits may reduce cases of severe ALRI, but a recent review found no evidence of association between surveillance interval (less than 2 weeks) and incidence. (1,5)
2. To ensure high specificity, as ALRI constitutes a minority (~10%) of all acute respiratory infections. Any impact of reduced exposure on ALRI incidence may be missed if ALRI cases are classified mistakenly with larger numbers of acute upper respiratory infections (AURI). To achieve specificity, all cases identified by fieldworkers should undergo physician examination and preferably chest X-ray (CXR). (5)
3. To take measures to make physicians' assessments blind and incorporate objective outcome assessments, as it was not possible for subjects of staff visiting homes to be blind to their intervention status.
This report's objectives are to describe these methods, evaluate the effectiveness of case-finding and identify any evidence of bias by intervention status. Analysis was carried out using Stata version 9.1. (6) An annual ethical review was conducted by the Centers for Disease Control and Prevention (CDC) and the institutional review boards of the Universities of California (Berkeley), del Valle de Guatemala and Liverpool (UK).
Study area and population
Following extensive feasibility studies, (7-13) a rural area of San Marcos in western Guatemala was selected. The indigenous population speaks mainly a Mayan language, Mam, and some Spanish. Wood is the main household fuel, burned indoors on open tires. Key features of the study area are presented in Table 1.
Study design and ALRI case-finding
The study design was a randomized controlled trial comparing ALRI incidence in children [less than or equal to] 18 months using the traditional three-stone tire (controls), with intervention homes using a flued wood stove (plancha): (7,14) 534 homes with either children under 4 months or a pregnant woman were randomized, and planchas constructed in 269. Sample size was determined to detect a 25% change in ALRI incidence of 0.5 episodes per child per year, at 5% significance, 80% power. Surveillance began after 5 weeks when the planchas were ready, from which time 518 children were followed until the age of 18 months, withdrawal or death. ALRI case-finding was carried out at four levels:
1. Weekly household visits by fieldworkers trained in WHO integrated management of childhood illness (IMCI) methods. (15)
2. Study physicians, working in local community centres to maintain blindness, undertook clinical assessments of children referred by fieldworkers, or self-referred. …