Exposure matrices of endotoxin, (1→3)-β-d-glucan, fungi, and dust mite allergens in flood-affected homes of New Orleans

Abstract

This study examined: (i) biocontaminant levels in flooded homes of New Orleans two years after the flooding; (ii) seasonal changes in biocontaminant levels, and (iii) correlations between biocontaminant levels obtained by different environmental monitoring methods. Endotoxin, (1→3)-β-d-glucan, fungal spores, and dust mite allergens were measured in 35 homes during summer and winter. A combination of dust sampling, aerosolization-based microbial source assessment, and long-term inhalable bioaerosol sampling aided in understanding exposure matrices. On average, endotoxin found in the aerosolized fraction accounted for <2% of that measured in the floor dust, suggesting that vacuuming could overestimate inhalation exposures. In contrast, the (1→3)-β-d-glucan levels in the floor dust and aerosolized fractions were mostly comparable, and 25% of the homes showed aerosolizable levels even higher than the dust-borne levels. The seasonal patterns for endotoxin in dust and the aerosolizable fraction were different from those found for (1→3)-β-d-glucan, reflecting the temperature and humidity effects on bacterial and fungal contamination. While the concentration of airborne endotoxin followed the same seasonal trend as endotoxin aerosolized from surfaces, no significant seasonal difference was identified for the concentrations of airborne (1→3)-β-d-glucan and fungal spores. This was attributed to the difference in the particle size; smaller endotoxin-containing particles can remain airborne for longer time than larger fungal spores or (1→3)-β-d-glucan-containing particles. It is also possible that fungal aerosolization in home environments did not reach its full potential. Detectable dust mite allergens were found only in dust samples, and more commonly in occupied homes. Levels of endotoxin, (1→3)-β-d-glucan, and fungi in air had decreased during the two-year period following the flooding as compared to immediate measurements; however, the dust-borne endotoxin and (1→3)-β-d-glucan levels remained elevated. No conclusive correlations were found between the three environmental monitoring methods. The findings support the use of multiple methods when assessing exposure to microbial contaminants.

Fig. 1.

Exposure matrices of endotoxin in flood-affected homes (n=35 in summer and 31 in winter). The lower and upper boundaries of the box specify the 25th and 75th percentiles, respectively. The line within the box indicates the median and the whiskers above and below the box indicate the 95th and 5th percentiles, respectively. * indicates statistically significant difference (paired t-test: p<0.05).

Fig. 2.

Exposure matrices of (1→3)-β-d-glucan in flood-affected homes (n=35 in summer and 31 in winter). The lower and upper boundaries of the box specify the 25th and 75th percentiles, respectively. The line within the box indicates the median and the whiskers above and below the box indicate the 95th and 5th percentiles, respectively. * indicates statistically significant difference (paired t-test: p<0.05).