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Abstract #162206

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Mushfiqur R. Tarafder¹, Theresa Gyorkos², Lawrence Joseph², and Hélène Carabin, DVM, PhD¹. (1) Department of Biostatistics and Epidemiology, University of Oklahoma Health Sciences Center, 801 N.E. 13th St., Oklahoma City, OK 73190, 405-271-2229 ext. 48081, mushfiqur-tarafder@ouhsc.edu, (2) Division of Clinical Epidemiology, McGill University, 687 Pine Avenue West, V Building, Montreal, QC H3G 1A1, Canada

Introduction / Objective: Public health issues have been raised about the increased incidence rates (IR) of diarrheal and upper respiratory tract (URTI) infections in day-care (DCC) settings. However, because of the variety of measures used, it is difficult to make comparisons and uptake of research results into public health practice may suffer. We assessed the impact of different definitions for episodes of illness and person-time on IR estimation.

Methods: Data from a 13-month-long cohort study of 2408 toddlers were used. Daily occurrence of illness, expected days of attendance, and daily absences, were recorded by DCC educators. Four definitions of IR using different lag times to define independent episodes (numerator) and at-risk time units to define child-at-risk (denominator) were compared.

Results: For diarrhea, the four different IR estimates were 1.41 episodes / 365 child-days at risk, 0.79 episodes / 52 child-weeks at risk, 0.81 episodes / 26 child-fortnights at risk, and 0.88 episodes / 12 child-months. For URTI, the four IRs were 7.64 episodes / 365 child-days at risk, 4.72 episodes / 52 child-weeks at risk, 5.05 episodes / 26 child-fortnight at risk, and 4.22 episodes / 12 child-months.

Conclusion: Different episodes and population-time definitions affect the estimation of the IR of diarrhea and URTI. Future research will investigate how they may also affect the estimation of the strength of risk factors for infection. This research will contribute to the development of a more standard approach to the measurement and reporting of incidence rates in epidemiological, occupational and environmental health studies.

Learning Objectives:

• 1. Describe different definitions of population-time (time unit of illness and at-risk time unit) used to calculate incidence rates in epidemiological studies.
• 2. Recognize the difficulty in comparing results from epidemiological studies using different population time definitions to calculate incidence rates.
• 3. Articulate the need for developing a more standard approach to the measurement and reporting of incidence rates in epidemiological studies.

Keywords: Epidemiology, Methodology

Presenting author's disclosure statement:

Any relevant financial relationships? No
Any institutionally-contracted trials related to this submission?

I agree to comply with the American Public Health Association Conflict of Interest and Commercial Support Guidelines, and to disclose to the participants any off-label or experimental uses of a commercial product or service discussed in my presentation.

• Slides (pdf) or Handout