Is the prevalence of peanut allergy increasing? A 5-year follow-up study in children in Montreal Moshe Ben-Shoshan, MD, a Rhoda S. Kagan, MD, b Reza Alizadehfar, MD, a Lawrence Joseph, PhD, c,d Elizabeth Turnbull, RN, c Yvan St Pierre, MA, c and Ann E. Clarke, MD, MSc d Montreal, Quebec, and Toronto, Ontario, Canada Background: Studies suggest that peanut allergy prevalence might be increasing, but these results have not yet been substantiated. Objective: We conducted a follow-up study to determine whether peanut allergy prevalence in Montreal is increasing. Methods: Questionnaires regarding peanut ingestion were administered to parents of children in randomly selected kindergarten through grade 3 classrooms between December 2000 and September 2002 and between October 2005 and December 2007. Respondents were stratified as (1) peanut tolerant, (2) never/rarely ingest peanut, (3) convincing history of peanut allergy, or (4) uncertain history of peanut allergy. Children in group 3 with positive skin prick test responses were considered to have peanut allergy. Children in groups 2 and 4 with positive skin prick test responses had peanut-specific IgE levels measured, and if the value was less than 15 kU/L, an oral peanut challenge was performed. Multiple imputation was used to generate prevalence estimates that incorporated respondents providing incomplete data and nonrespondents. Results: Of 8,039 children surveyed in 2005-2007, 64.2% of parents responded. Among those providing complete data, the prevalence was 1.63% (95% CI, 1.30% to 2.02%) in 2005-2007 versus 1.50% (95% CI, 1.16% to 1.92%) in 2000-2002. After adjustment for missing data, the prevalence was 1.62% (95% credible interval, 1.31% to 1.98%) versus 1.34% (95% credible interval, 1.08% to 1.64%), respectively. The differences between the prevalences in 2005-2007 and 2000-2002 were 0.13% (95% credible interval, 20.38% to 0.63%) among those providing complete data and 0.28% (95% credible interval, 20.15% to 0.70%) after adjustment for missing data. Conclusions: This is the first North American study to document temporal trends in peanut allergy prevalence by corroborating history with confirmatory tests. The results suggest a stable prevalence, but wide CIs preclude definitive conclusions. (J Allergy Clin Immunol 2009;123:783-8.) Key words: Peanut allergy, prevalence, skin prick test, peanut-spe- cific IgE, food challenge, epidemiology During the last 2 decades, the medical literature reports an increase in allergic diseases, 1 including peanut allergy. Based pri- marily on longitudinal studies conducted in the United States and the Isle of Wight, 2,3 it is speculated that the prevalence of peanut allergy might have doubled over 5 years. However, this apparent increase might be attributed to a failure to apply rigid and inclu- sive diagnostic criteria, methodological differences, overlapping CIs, and/or nonresponse bias. Between December 2000 and Sep- tember 2002, we conducted the first Canadian study to estimate the prevalence of peanut allergy 4 ; ours was also the first study in North America to corroborate history with confirmatory testing and the largest study worldwide to fully incorporate these tech- niques. 4 Although our estimate of peanut allergy prevalence of 1.5% (95% CI, 1.16% to 1.92%) in Montreal exceeds North American and most European estimates, 2-5 it cannot be concluded that the prevalence of peanut allergy is increasing. Our study did not evaluate prevalence over time, and comparisons with other studies are hampered by differences in methodologies and sam- pling frames, overlapping CIs, and nonresponse bias. To deter- mine whether the prevalence of peanut allergy is increasing, we conducted a follow-up study between October 2005 and Decem- ber 2007 using the identical methodology and sampling frame of our 2000-2002 study. It is only by replicating a methodology that corroborates clinical history with comprehensive diagnostic test- ing, sampling an identical population, ensuring an adequate sam- ple size, and adjusting for nonresponse that we can determine whether this speculated increase is real. METHODS Sampling frame We conducted a cross-sectional study, revisiting the schools participating in our original study 4 and randomly selecting kindergarten through grade 3 class- rooms. The study was approved by the Institutional Review Board of the McGill University Health Centre, school boards, individual schools, and par- ents. Children were recruited between October 2005 and December 2007. Public schools refusing to participate in the follow-up study were replaced by other randomly selected schools. For our 2-sample design (ie, a comparison of the prevalence between the 2000-2002 and 2005-2007 studies), we required 4,315 children in each sample to estimate the prevalence to an accuracy of at least 60.625% with a 95% CI, From a the Department of Pediatrics, Division of Clinical Immunology/Allergy and Rheu- matology, McGill University Health Centre, Montreal; b the Department of Pediatrics, North York General Hospital, University of Toronto; c the Department of Medicine, Division of Clinical Epidemiology, McGill University Health Centre; d the Depart- ments of Epidemiology and Biostatistics, McGill University, Montreal; and the Department of Medicine, Divisions of Clinical Epidemiology and Clinical Immunol- ogy/Allergy, McGill University Health Centre. Supported by the Canadian Institutes of Health Research (MOP-77584); the Allergy, Genes and Environment Network Centres of Excellence (AllerGen NCE); Anaphy- laxis Canada; the Canadian Allergy, Asthma and Immunology Foundation; and Novartis Pharmaceuticals. Dr Clarke received a $2500 unrestricted grant from Novartis Pharmaceuticals. Drs Joseph and Clarke are National Scholars of Fonds de la recherche en sante ´ du Que ´bec. Disclosure of potential conflict of interest: M. Ben-Shoshan receives grant support from AllerGen. R. S. Kagan is on the Board of Directors for the Canadian Society of Allergy and Clinical Immunology (CSACI) and receives honoraria for speaking for King Pharmaceuticals and Merck Frosst. R. Alizadehfar is on the speakers’ bureau for Paladian Pharma and receives research support from Allergen. A. E. Clarke receives grant support from AllerGen; Anaphylaxis Canada; and the Canadian Allergy, Asthma and Immunology Foundation. The rest of the authors have declared that they have no conflict of interest. Received for publication October 10, 2008; revised January 29, 2009; accepted for pub- lication February 2, 2009. Reprint requests: Ann E. Clarke, MD, MSc, McGill University Health Centre, 687 Pine Ave West, V Building, Room V2.05, Montreal, Quebec H3A 1A1, Canada. E-mail: Ann.Clarke@mcgill.ca. 0091-6749/$36.00 Ó 2009 American Academy of Allergy, Asthma & Immunology doi:10.1016/j.jaci.2009.02.004 783