Suwannee Uthaisangsook, MD¹ , Sirirat Bunarsa, MS² , Sagoontee Inkate, MD³ , Boonchua Dhorranintra, MD, Dr Med⁴

Background: Fungal sensitization is strongly associated with asthma severity and increased outdoor spore exposure correlates with higher asthmarelated hospitalization. However, data on outdoor airborne fungal spores in lower northern Thailand are limited.

Objective: To assess changes in outdoor airborne mold spore patterns and counts over two distinct periods, ten years apart, in Phitsanulok, lower northern Thailand, to optimize allergic disease management.

Materials and Methods: Mold spores were collected from August 2013 to July 2014 and from August 2022 to July 2023, using a Burkard seven-day volumetric spore trap positioned 15 meters above ground. Exposed slides were stained for microscopic analysis, and meteorological data were recorded.

Results: Monthly outdoor airborne mold spore levels ranged from 336.5 to 939.6 spores/m³ (2013-2014) and 257.7 to 821.8 spores/m³ (2022-2023), with peaks in June (2013-2014) and May to June (2022-2023). Cladosporium spp. was the most abundant spore type in both periods. Rankings for the sixth to eleventh spore types were consistent, while the top five varied. Cladosporium spp. peaked in July 2014 and May to June 2023, approaching 500 spores/m³, a threshold for allergic risk. Overall, total spore concentrations were highest in the early rainy season, as rainfall increased from late April through June. In both periods, many spore types exhibited lower concentrations during months with the lowest relative humidity (March to April) and during peak rainfall (September).

Conclusion: Cladosporium spp. accounted for the majority of outdoor mold spores. Many spore types increased at the onset of the rainy season and decreased during months with the lowest humidity.

Received 3 April 2026 | Revised 5 May 2026 | Accepted 12 May 2026

J Med Assoc Thai 2026;109(6):547-58

DOI: 10.35755/jmedassocthai.2026.6.04535