Objectives: There are no nationally representative hearing loss (HL) prevalence data available for Canadian youth using direct measurements. The present study objectives were to estimate national prevalence of HL using audiometric pure-tone thresholds (0.5 to 8 kHz) and or distortion product otoacoustic emissions (DPOAEs) for children and adolescents, aged 3 to 19 years. Design: This cross-sectional population-based study presents findings from the 2012/2013 Canadian Health Measures Survey, entailing an in-person household interview and hearing measurements conducted in a mobile examination clinic. The initial study sample included 2591 participants, aged 3 to 19 years, representing 6.5 million Canadians (3.3 million males). After exclusions, subsamples consisted of 2434 participants, aged 3 to 19 years and 1879 participants, aged 6 to 19 years, with valid audiometric results. Eligible participants underwent otoscopic examination, tympanometry, DPOAE, and audiometry. HL was defined as a pure-tone average >20 dB for 6- to 18-year olds and ≥26 dB for 19-year olds, for one or more of the following: four-frequency (0.5, 1, 2, and 4 kHz) pure-tone average, high-frequency (3, 4, 6, and 8 kHz) pure-tone average, and low-frequency (0.5, 1, and 2 kHz) pure-tone average. Mild HL was defined as >20 to 40 dB (6- to 18-year olds) and ≥26 to 40 dB (19-year olds). Moderate or worse HL was defined as >40 dB (6- to 19-year olds). HL in 3- to 5-year olds (n = 555) was defined as absent DPOAEs as audiometry was not conducted. Self-reported HL was evaluated using the Health Utilities Index Mark 3 hearing questions. Results: The primary study outcome indicates that 7.7% of Canadian youth, aged 6 to 19, had any HL, for one or more pure-tone average. Four-frequency pure-tone average and high-frequency pure-tone average HL prevalence was 4.7 and 6.0%, respectively, whereas 5.8% had a low-frequency pure-tone average HL. Significantly more children/adolescents had unilateral HL. Mild HL was significantly more common than moderate or worse HL for each pure-tone average. Among Canadians, aged 6 to 19, less than 2.2% had sensorineural HL. Among Canadians, aged 3 to 19, less than 3.5% had conductive HL. Absent DPOAEs were found in 7.1^E% of 3- to 5-year olds, and in 3.4^E% of 6- to 19-year olds. Among participants eligible for the hearing evaluation and excluding missing data cases (n = 2575), 17.0% had excessive or impacted pus/wax in one or both ears. Self-reported HL in Canadians, aged 6 to 19, was 0.6 E% and 65.3% (aged 3 to 19) reported never having had their hearing tested. E indicates that a high sampling variability is associated with the estimate (coefficient of variation between 16.6% and 33.3%) and should be interpreted with caution. Conclusions: This study provides the first estimates of audiometrically measured HL prevalence among Canadian children and adolescents. A larger proportion of youth have measured HL than was previously reported using self-report surveys, indicating that screening using self-report or proxy may not be effective in identifying individuals with mild HL. Results may underestimate the true prevalence of HL due to the large number excluded and the presentation of impacted or excessive earwax or pus, precluding an accurate or complete hearing evaluation. The majority of 3- to 5-year olds with absent DPOAEs likely had conductive HL. Nonetheless, this type of HL which can be asymptomatic, may become permanent if left untreated. Future research will benefit from analyses, which includes the slight HL category, for which there is growing support, and from studies that identify factors contributing to HL in this population.

We have evaluated a flow cytometric method that allows assessment of micronucleated reticulocytes (MN-RETs) in microliter quantities of peripheral blood and compared results using this assay with those of established microscopic methods of scoring bone marrow and peripheral blood from rats treated with well-characterized genotoxic agents. Young reticulocytes (RETs) are labeled with FITC–anti-CD71 (transferrin receptor) and micronuclei with propidium iodide (with RNase treatment). Red blood cells parasitized with Plasmodia serve as a calibration standard for DNA content. Microscopic scoring used acridine orange (AO) staining of methanol-fixed slides or supravital AO staining. The effect of the rat spleen on the parameters evaluated was determined by comparing age- and sex-matched normal and splenectomized rats treated with cyclophosphamide, cis-platin, or vinblastine under treatment conditions that established a steady-state frequency of MN-RETs in the bone marrow and peripheral blood compartments. The data demonstrate the sensitivity and reproducibility of the flow cytometric assay in the Sprague-Dawley rat, and comparative studies using identical blinded samples at multiple laboratories show that inter- and intra-laboratory reproducibility is much higher with the flow method than with the microscopic methods currently employed for regulatory studies. A significant effect of splenic selection against genotoxicant-induced MN-RETs was observed with each of the three scoring methodologies, despite the fact that the flow and supravital AO techniques restrict analysis to the youngest fraction of RETs. The high precision of flow-based measurements also demonstrated a slight but statistically significant level of selection against spontaneously arising MN-RET. Despite these spleen effects, assay sensitivity for blood-based analyses was maintained by the flow method as it was shown to have superior counting statistics, lower variability, and higher sensitivity than manual scoring. The data suggest that flow cytometric assessment of micronucleus induction can be integrated into routine toxicity testing, eliminating the need for a separate bioassay.

Traditionally, the dicentric chromosome assay (DCA) has been used to derive biological dose estimates for unknown radiological exposures. While sensitive, this assay requires highly trained evaluators and is extremely time consuming. The cytokinesis-block micronucleus (CBMN) assay has been suggested as an alternative to the DCA, as it is much faster to evaluate samples and requires less technical expertise. In order to validate this assay for triage biodosimetry, dose–response curves were generated for six donors at eight doses of gamma-radiation (0–4.0 Gy). Each sample was evaluated by 12 individuals, among three different laboratories and the incidence of micronuclei was determined after counting 50–500 binucleated cells. This study demonstrated that the CBMN assay was capable of detecting radiation doses ≥1 Gy after scoring only 200 binucleated cells. As such, the CBMN assay may provide a sensitive and reliable technique for deployment as an initial screening tool in a large-scale radiological emergency where large numbers of biological dose estimates are required.