A new study presented at ASM Microbe 2025 has provided strong evidence that higher levels of fungal spores in the air are closely associated with spikes in influenza and COVID-19 cases. The findings suggest that tracking airborne fungal spores could serve as an effective early warning tool for anticipating respiratory virus outbreaks, aiding public health preparedness.

The research, conducted by scientists at Lynn University (Boca Raton, FL, USA), found that measuring fungal spore levels outdoors could be a reliable method for forecasting rises in flu and COVID-19 cases, particularly in the autumn months. The team aimed to explore the short-term effects of environmental factors—specifically fungal spores and pollen—on the occurrence or intensification of viral respiratory infections like influenza and COVID-19. For this investigation, they analyzed daily data from 2022 to 2024 in two major healthcare regions in Puerto Rico: San Juan and Caguas. Puerto Rico provides a distinct setting for this research, given its continuous, endemic presence of airborne fungi and pollen throughout the year. Although these environmental elements are already known to influence conditions such as asthma and allergies, their relationship to viral infection patterns has not been extensively studied. The dataset included daily case counts for flu and COVID-19, along with the corresponding measurements of airborne fungal spores and pollen for those dates.

To determine whether elevated environmental exposure levels could predict upcoming viral infection spikes, the researchers applied both statistical analyses and machine learning techniques. These models evaluated whether high levels of fungal spores or pollen were linked to increased flu and COVID-19 case counts either within the same week or the following week—a concept referred to as a "lag-effect." The results revealed a strong correlation between high airborne fungal spore concentrations and increases in respiratory virus infections. This association did not hold for pollen levels. In many cases, a rise in fungal spore concentrations was followed by a noticeable increase in infection numbers just days later. The predictive models were particularly effective in forecasting infection surges during the fall season across both study regions—San Juan and Caguas. Pollen levels, on the other hand, did not demonstrate any predictive capability. As a next step, the researchers intend to examine whether these environmental factors are also linked to more severe health outcomes, such as hospital admissions or deaths. They also plan to investigate whether similar environmental-infection patterns occur in geographic regions outside of Puerto Rico.

“The findings from our study suggest that monitoring airborne fungal spore levels could help predict short-term outbreaks (spikes) of flu and COVID-19, giving public health systems an early warning signal,” said presenting study author Félix E. Rivera-Mariani, Ph.D. “Our findings also highlight the potential role of environmental factors—not just person-to-person spread—in contributing to the incidence of respiratory viral infections. That could open new doors for targeted public health alerts, especially in areas with high outdoor airborne fungi.”

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