Revista Panamericana de Salud Pública
Print version ISSN 1020-4989
ORELLANO, Pablo Wenceslao and REYNOSO, Julieta Itatí. New method for determining endemic levels. Rev Panam Salud Publica [online]. 2011, vol.29, n.5, pp. 309-314. ISSN 1020-4989. http://dx.doi.org/10.1590/S1020-49892011000500002.
OBJECTIVE: Design an instrument for determining endemic levels or ranges using simple calculations; identify and estimate the parameters related to the dynamic transmission of communicable diseases. METHODS: The parameters for establishing a theoretical curve of expected incidence based on the logistic growth model were identified. The parameters were estimated by nonlinear regression based on the cumulative incidence data from the previous five years. The weekly cumulative incidence of cases of influenza-like illness in Argentina in 2009 was used as an example. It was compared to the 2004-2008 case series in order to determine the cumulative and non-cumulative endemic levels. RESULTS: According to the cumulative endemic levels identified, the country entered the outbreak area in week 2. The data from previous years showed that the maximum expected number of cases or carrying capacity (K) was 1 090 660. When the non-cumulative levels were considered, the outbreak was present in 34 out of 51 weeks. A range of 1.05 to 1.13 was estimated for the basic reproductive rate (R0) in the non-epidemic period from 2004-2008. CONCLUSIONS: The new method facilitated the determination of endemic levels using a simple procedure with the identification of parameters that are important for transmission. Although it has limitations such as the fact that the equation used is more appropriate for evaluating diseases with a pronounced annual cycle and less accurate for cycles of less than 1 year, it can be considered a valuable alternative method for determining endemic ranges and a new contribution to the study of epidemic outbreaks at local health surveillance levels.
Keywords : Epidemiologic models; decision support techniques; disease outbreaks; influenza A virus; H1N1 subtype; Argentina.