Does outpatient laboratory testing represent influenza burden and distribution in a rural state?

Laboratory testing results are often used to monitor influenza illness in populations, but results may not be representative of illness burden and distribution, especially in populations that are geographically, socioeconomically, and racially/ethnically diverse.

Descriptive epidemiology and chi-square analyses using demographic, geographic, and medical condition prevalence comparisons were employed to assess whether a group of individuals with outpatient laboratory-confirmed influenza illness during September-November 2009 represented the burden and distribution of influenza illness in New Mexico (NM).

The outpatient group was identified via random selection from those with positive influenza tests at NM laboratories. Comparison groups included those with laboratory-confirmed H1N1-related influenza hospitalization and death identified via prospective active statewide surveillance, those with self-reported influenza-like illness (ILI) identified through random digit dialing, and the NM population.

This analysis included 334 individuals with outpatient laboratory-confirmed influenza, 888 individuals with laboratory-confirmed H1N1-related hospitalization, 39 individuals with laboratory-confirmed H1N1-related death, 334 individuals with ILI, and NM population data (N = 2,036,112). The outpatient laboratory-confirmed group had a different distribution of demographic and geographic factors, as well as prevalence of certain medical conditions as compared to the groups of laboratory-confirmed H1N1-related hospitalization and death, the ILI group, and the NM population.

The outpatient laboratory-confirmed group may reflect provider testing practices and potentially healthcare-seeking behavior and access to care, rather than influenza burden and distribution in NM during the H1N1 pandemic.