Feasibility of using community pharmacy sales of over-the-counter respiratory products as a syndromic surveillance indicator: a pilot study from Sofia, Bulgaria

Introduction Data on sales of pharmaceutical products (SPP) for symptomatic treatment of acute respiratory diseases can be a reliable indicator providing initial information before official surveillance systems. This pilot study aimed to develop a framework for collecting community pharmacy sales data and assess the feasibility of using these data as a complementary indicator of respiratory infection activity. Methods Products were selected through observation of prime-time television advertisements during February–March 2025, expert review, and a survey of 97 community pharmacists. Retrospective monthly sales data for selected product categories were obtained from two community pharmacies in Sofia for October 2024–April 2025. Sales were analysed using descriptive statistics, the Friedman test, and post-hoc Wilcoxon signed-rank tests with Bonferroni correction. Results Mean SPP vary from 121.06 units for antivirals to 685.96 units for antipyretics. Antivirals showed the greatest relative monthly variability ( R = 216.4, CV = 64.78), followed by food supplements ( R = 160.16, CV = 33.23). Sales of products for sore throat were comparatively stable ( R = 103, CV = 18.62) with limited temporal variation during the observation period. Antipyretic and antiviral sales reached their highest levels in January 2025, accounting for 19.14 and 32.00% of their respective total sales during the observation period. The January increase temporally coincided with the peak in reported acute respiratory infections in Sofia during week 4 of 2025. However, pairwise comparisons between January and the other months were not statistically significant after Bonferroni correction. Conclusion Pharmacy sales data showed preliminary potential for monitoring local respiratory infection trends; however, larger prospective multicenter studies using standardized product classifications and higher-frequency sales data are needed to evaluate their contribution to complementary respiratory syndromic surveillance.