Survey of South Florida’s Pollen and Spore Counts

The treatment of allergic rhinitis in South Florida has always been problematic due to the dearth of knowledge of the nature of pollen and outdoor mold exposure in this region. The Department of Allergy/Immunology at Miami Children’s Hospital, in association with well known aerobiologist Mary Jelks, M.D., has began a serious scientific survey of our region’s pollen and mold spores. Their data is summarized below.

The first finding was that pollen counts are surprisingly low. Compared to Tallahassee and Sarasota, the total average pollen counts were more than tenfold lower. Also, South Florida’s mold spore counts are about half of those of other areas of the state, but they are still higher than those of the country’s drier regions. One interesting finding was that pollen and mold counts correlated with easterly winds, indicating that the source of the airborne allergens lies to the West. This would suggest that patients residing close to the ocean would generally have less exposure to outdoor allergens. One of the most interesting findings was that in 3 of the 4 years studied, there was a correlation with higher mold counts and ER visits for asthma.

In addition, this survey allows for generalities about the seasonal pattern of pollens and mold in out area. For instance, grasses bloom year-round, with counts tending to be higher in April and May. Although individual grasses cannot be reported individually, Bermuda, Bahia, and Johnson grasses are among the most important. St. Augustine grass releases insignificant amounts of pollen, but the thick turf harbors mold spores that are dispersed by mowing.

Weed pollens such as ragweed, nettle, dog fennel, and baccharis are also seen throughout the year, with higher counts generally seen in the fall. However, the peak counts of both the grasses and weeds are very low compared to some other regions. Mold spores are also released throughout the year and may be the source of the most clinically relevant outdoor allergens.

There are, however, some significant seasonal peaks of tree pollens in our area. The tree pollen season generally runs from mid-December through the early spring, consisting mostly of Oak, Juniper, Bald Cypress, and Australian Pine. There are exceptions to this pattern, such as the fall appearance of Australian Pine and the year-round presence of Queen Palm. Pollen from the infamous Melaleuca is also seen during most of the year, but some studies have suggested that its pollen is not allergenic.

Although airborne pollen is present year-round in South Florida, the counts are low and may not be a significant cause of allergy symptoms. Mold, whose spore counts correlated with ER visits for asthma, are likely a more important outdoor allergen. Since our overall outdoor allergen levels are lower than other regions of the country, indoor allergen exposure (dust mite, indoor molds, animal dander) is probably the more important factor for many of South Florida’s allergy sufferers.