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Seasonal Fine and Coarse Culturable FungalConstituents and Concentrations from Indoor andOutdoor Air Samples Taken from an Arid EnvironmentLinda C. Mota a , Shawn G. Gibbs a , Christopher F. Green b , Carissa M. Flores a , Patrick M.Tarwater a & Melchor Ortiz aa The University of Texas School of Public Health , El Paso, Texasb Department of Biology , University of Cincinnati, Clermont College , Cincinnati, OhioPublished online: 27 Jul 2010.

To cite this article: Linda C. Mota , Shawn G. Gibbs , Christopher F. Green , Carissa M. Flores , Patrick M. Tarwater &Melchor Ortiz (2008) Seasonal Fine and Coarse Culturable Fungal Constituents and Concentrations from Indoor and OutdoorAir Samples Taken from an Arid Environment, Journal of Occupational and Environmental Hygiene, 5:8, 511-518, DOI:10.1080/15459620802208636

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Journal of Occupational and Environmental Hygiene, 5: 511–518ISSN: 1545-9624 print / 1545-9632 onlineCopyright c© 2008 JOEH, LLCDOI: 10.1080/15459620802208636

Seasonal Fine and Coarse Culturable Fungal Constituentsand Concentrations from Indoor and Outdoor Air SamplesTaken from an Arid Environment

Linda C. Mota,1 Shawn G. Gibbs,1 Christopher F. Green,2

Carissa M. Flores,1 Patrick M. Tarwater,1 and Melchor Ortiz1

1The University of Texas School of Public Health, El Paso, Texas2Department of Biology, University of Cincinnati, Clermont College, Cincinnati, Ohio

This study was undertaken to determine the normal indoorand outdoor airborne culturable fungal constituents andconcentrations of an arid environment. Air samples weretaken with two-stage, ambient, culturable sampler systems andanalyzed for nine specific fungal genera from 50 homes as arepeated measure during each season of the year. These homeshad no previous histories of indoor air quality issues. Thisstudy detected seasonal differences for the arid environmentbetween different culturable fungal concentrations across thetwo size ranges. The highest concentrations were during fall,in the outdoor fine-size range. The lowest concentrations werethe indoor coarse concentrations in the spring. From thisstudy it can be concluded that Cladosporium spp. had thehighest concentrations during fall in an arid environment. Theoverall findings suggest that Cladosporium had concentrationsgreater than the other genera evaluated, specifically, thefall outdoor fine concentrations. Seasonality was found tobe a key factor in determining the variability of fungalconstituents and concentrations within the arid indoor andoutdoor environments. The fine-size range was 12 times and 6times greater than the coarse-size range for indoor and outdoorsamples, respectively, which accounted for the majority offungal organisms. In addition, the results from this studyin an arid climate differ from those conducted in a moisterclimate.

Keywords air samples, Aspergillus, Bioaerosol, Cladosporium,fungi

Address correspondence to Shawn G. Gibbs, The University ofTexas Health Science Center, School of Public Health, 1100 N.Stanton, Suite 110C, El Paso, TX 79902; e-mail: shawn.g.gibbs@uth.tmc.edu.

INTRODUCTION

F ungal organisms are a rising concern related to indoor airquality and human health effects. Health effects related to

fungal exposures may include shortness of breath, rhinitis, andother respiratory symptoms, as well as muscle or joint pain,

fatigue, weakness, and headache.(1,2) There is also evidencethat fungal organisms act as asthma and allergy triggersin small children.(3) Although no threshold limit values forfungal bioaerosols exist, studies suggest a range of fungalconcentrations can result in negative human health effects.(4−7)

There are certain genera of fungi that are related to moistureproblems, if found in air samples. These include Stachybotrys,Fusarium, Trichoderma, and Aspergillus. Stachybotrys char-tarum, for example, has the ability to produce mycotoxins thatpotentially could have immunosuppressant effects, (8) as doa number of other toxin producers. The most common generapreviously found in indoor air are Penicillium, Aspergillus, andCladosporium.(9−14)

Fungal constituents and concentrations are dynamic andhighly dependent on weather conditions, with research indicat-ing the maximum concentrations occurring when temperaturesare 25–30◦C.(15) There is a strong observable relationshipbetween the season and airborne concentrations of fungi, withlower concentrations present in the winter and higher con-centrations present in the summer and fall.(10,11,16) Althoughthe constituents of fungal bioaerosols are dynamic and notuniform, the peak concentrations normally are recovered whenthe wind speed and temperature reach levels that break conidialchains. Typically, this occurs during the dry season in the lateafternoon.(17)

A study done in the Tulsa, Oklahoma, area concludedthat the dry weather allowed buildup of dry-air spores andincreases in wind speed, dew point, air pressure and changingweather conditions associated with thunderstorms allowedfungal spores to be highly dispersed.(18) These conditions aresimilar to those found in the El Paso, Texas, area during thesummer; however, climatic conditions in Tulsa are not similarto those in El Paso for the rest of the year.(18) The studyby Shelton et al.(19) indicates the importance of developingan understanding of the types, concentrations, and behaviorsof fungal organisms within indoor and outdoor environmentsbecause they may be significant indicators of future human

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health exposures. Shelton et al. presented the results of multipleevaluations of fungi in buildings and outdoor environmentsthroughout the United States, and 74 of the 1717 were fromthe arid southwest. Exposure to fungi in a residential settingcould have the largest impact on the health of children andimmunocompromised residents, since these individuals aremore susceptible and more apt to spend time indoors.

The hypothesis of this study is that there would be seasonalvariability with the constituents and concentrations of cultur-able fungal bioaerosols, and that this variability, measured inan arid climate, would differ from those previously reportedin non-arid climates. The objective of this study was to detectpossible differences between fine and coarse culturable fungalconcentrations during each season; specifically, to provideinformation lacking in the research on the normal indoor airenvironment for non-water-damaged homes within an aridenvironment.

Because particle size plays an important role in particleaerosolization and penetration into the respiratory tract, it wasincluded in this study as a significant component for investiga-tion, since finer particles are more apt to become aerosolized,are retained in the air column longer, and may have greaterhealth impacts. It was hypothesized that the fine-to-coarse ratiowould differ between indoor and outdoor environments dueto the air movement necessary to aerosolize larger particles.This could provide a first step in the determination of whenvulnerable individuals are more likely to experience healthissues resulting from residential indoor air exposure to fungalorganisms in an arid environment.

METHODS

Sampling SitesThis study was done to determine normal culturable fun-

gal constituents and concentrations in an arid environmentthroughout the year. Air samples initially were taken from50 different houses in the El Paso, Texas, area. Houses wereidentified when a solicitation for study participation was sentto faculty, staff, and students at the University of Texas Schoolof Public Health, El Paso Regional Campus, and the Universityof Texas at El Paso. Houses were single-story homes with noattics or basements. Sizes ranged from 1200 to 2500 squarefeet, with an average size of 1400 square feet. The age rangedbetween 40 years and 5 years, with the average age 25 years.

Because the houses were recruited through a conveniencesample it cannot be stated for certain that they are repre-sentative of all homes in the region. These homes had nohistorical indoor air quality issues. All homes used evaporativecooling technology and had gas furnaces. Repeated measureswere taken for each house, with a sampling visit made duringeach season: spring (March, April, May), summer (June, July,August), fall (September, October, November), and winter(December, January, February) from March 2005 throughFebruary 2006.

The traditionally accepted start dates of each season forthe northern hemisphere were used, and houses were not

sampled within 5 days of the beginning or end of the season.Meteorological observations were not used to confirm the startof seasons. All sampling was conducted at the convenience ofresidents. Repeated sampling for each house was conductedduring one of two sampling blocks (morning: 8 a.m. to noon;afternoon: 1 p.m. to 5 p.m.).

Sampling MethodologyAir sampling methodology was the same used by Green

et al.(20) and Gandara et al.(21) During each visit, a visualinspection was conducted to determine existing water or fungaldamage and to assess any structural issues. Indoor and outdoormeasurements of temperature, relative humidity, and baromet-ric pressure were collected using a portable weather station(Traceable Digital Barometer Module Calibration Control Co.,Friendswood, Texas)

A two-stage, ambient, culturable sampler system (TE-10-860; Tisch Environmental, Cleves, Ohio) was used forcollecting air samples. This apparatus divides particles intofine- (1–8 µm) and coarse- (>8 µm) size ranges. The fine-size range represents particles that can reach human lungs,whereas the coarse-size range represents particles that depositinto upper airways. An air pump, at a flow rate of 28.3 L/min,was connected to the impactor.

However, some overlap of particle sizes near the cutoff pointmay occur on each plate. Airborne particles are collected byimpaction onto collection media at each stage of the sampler,depending on their aerodynamic equivalent diameter. Eachstage is loaded with 100-mm × 15-mm plastic Petri dishes with20 mL of malt extract agar (MEA) media (Difco Laboratories,Sparks, Md.) as the collection media, per manufacturer’srecommendations. Multiple aseptic techniques, both in situ andin vitro, were used to decrease potential cross-contaminationof the samples throughout the study.

A positive control and a negative control were used foreach medium. The positive control for MEA was Candidaalbicans (ATCC 10231). The negative control consisted of twoPetri dishes of MEA carried into the field during the collectionprocess and, subsequently, processed and incubated in the samemanner as the rest of the samples.

Four samplers (two samplers side by side, at a meter’sheight, both inside and outside the home) were operatedsimultaneously. Only a single visit was made per day per seasonfor each home. The inside samplers were placed in the mainliving area, and the two outside samplers were placed withintwo meters of the front door. Duplicate air samples were takenfor 10 and 15 min (providing four samples per visit per stagefor both indoor and outdoor samples).

While the sampling periods were longer than usual, thiswas necessary to obtain the maximum fungal organisms, sincefungal recoveries were very low in the authors’ preliminarywork. All media was prepared fresh to help prevent des-iccation during the longer sampling periods. The minimumnumber of recoverable organisms was 2 CFU/m3, and themaximum number of recoverable organisms was 706 CFU/m3.Because the identified number of organisms recovered

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TABLE I. Total Mean Fungal Concentration (CFU/m3) and Standard Deviation for Indoor and Outdoor Samplesat Different Size Ranges

Particle Spring Summer Fall WinterType/Location (n = 50) (n = 48) (n = 47) (n = 39) p-Value

Coarse, indoor 8 ± 9 10 ± 15 18 ± 51 8 ± 25 0.196Coarse, outdoor 16 ± 23 15 ± 11 39 ± 79 9 ± 9 0.002Fine, indoor 45 ± 41 87 ± 103 125 ± 131 38 ± 49 <0.001Fine, outdoor 54 ± 54 94 ± 91 212 ± 222 46 ± 53 <0.001Total indoor 53 ± 47 98 ± 115 144 ± 147 46 ± 60 <0.001Total outdoor 70 ± 66 108 ± 94 252 ± 265 55 ± 60 <0.001

n = number of homes evaluated.

was in a low frequency, no positive-hole correlation wasconducted.

Sample AnalysisSamples were incubated at 25◦C for 10 days. The plates

were checked, and colonies were enumerated at 24 hr, 48 hr,5 days, and 10 days to allow slow-growing fungi the op-portunity to develop. Bacterial growth on MEA was not anissue. After incubation, the fungal colonies from the Petridishes were identified via microscopy and morphology to thegenus.(22) Using preliminary samples as a guide, this studyidentified eight genera (Alternaria, Bipolaris, Stemphylium,Phoma, Aspergillus, Cercospora, Cladosporium, Rhizopus)that were prevalent in preliminary samples. Stachybotrys alsowas identified because homeowners were interested in thisorganism. No attempt was made to identify other organisms,and all other organisms were grouped into the category reportedas “Unknown.”

Statistical AnalysisThe data of concentrations of various culturable fungal

organisms, size ranges, and seasons throughout the year ispresented as the proportion of all houses with undetectableconcentrations and the median value for those houses withdetectable levels of concentration. Statistical analyses ofdifferences in concentrations due to season of the year wereperformed on data grouped into indoor and outdoor samples forcoarse, fine, and total organisms. Repeated measure analysisof variance (ANOVA) was performed to detect any significantchange in fungal concentrations.

Although the distributions of concentrations were likelyskewed, the sample sizes in each season were large enoughthat the normality assumption for ANOVA can be met by thecentral limit theorem. That is, the sampling distribution of thesample means can be assumed to be approximately normallydistributed, as is required to use ANOVA. In addition, for theANOVA analysis only, the data points that were below thelimit of detection were set as the lowest fungal concentrationdetected, divided by 2. Furthermore, the descriptive statisticsfor the analysis of the combined groups across seasonsare presented as means and standard deviations. Statistical

Analysis Software 9.1.3 (SAS Institute, Cary, N.C.) was usedfor statistical analyses of the data.

Fifty homes were recruited for the first sampling. Thatnumber declined to 39 by the final sampling (spring, n = 50;summer, n = 48; fall, n = 47; winter, n = 39) as a result ofstudy participants opting not to continue in the study. Once ahome did not participate in one season of the study, it was notallowed to participate again. Statistical tests were performedto demonstrate possible differences between seasonality, withrespect to different fungal type.

RESULTS

T able I shows the summary statistics for the total culturablefungal concentrations (CFU/m3) for the nine fungal gen-

era that were evaluated with different size ranges and samplelocations throughout the year. The highest concentrationswere found during fall, in the fine-size range. The lowestconcentrations were the indoor coarse concentrations foundduring spring. Differences among seasons in coarse indoorconcentrations were not statistically significant. However,there were significant differences due to season for all othergroups of concentrations. Specifically, the outdoor coarsefungal concentrations for spring, winter, and fall were notsignificant (p > 0.05), although fall was different (p < 0.05)from the other seasons. Fine indoor, fine outdoor, total indoor,and total outdoor fungal concentrations all showed the sameseasonal variation, with spring, summer, and fall different(p < 0.05) from each other, and winter only different fromfall (p < 0.05). The coarse indoor and outdoor concentrationswere always lower and different from their fine counterparts,regardless of season (p < 0.05). A fine-to-coarse ratio wascalculated for each season, and the mean indoor ratio (spring,12.8 ± 14.6; summer, 13.8 ± 11.8; fall, 13.2 ± 9.8; winter,13.4 ± 13.6) was nearly twice that of the outdoor ratio (spring,5.2 ± 4.6; summer, 7.4 ± 5.3; fall, 6.8 ± 3.4, winter, 6.8 ± 5.3)across seasons.

In Table II, the median coarse indoor culturable fungalconcentrations for the nine fungal genera that were evaluatedare shown with respect to season. Cladosporium had thehighest concentrations evaluated during spring. Stemphyliumand Bipolaris had the highest evaluated concentration during

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TABLE II. Coarse Indoor Fungal Concentrations

Genus

Spring(n = 50)

(%, CFU/m3)

Summer(n = 48)

(%, CFU/m3)

Fall(n = 47)

(%, CFU/m3)

Winter(n = 39)

(%, CFU/m3)

Alternaria 44, 2 42, 1 38, 1 90, 1Bipolaris 96, 1 65, 3 26, 2 59, 1Stemphylium 96, 1 54, 3 13, 2 79, 1Phoma 96, 1 52, 1 60, 1 46, 1Aspergillus 38, 2 46, 1 68, 1 62, 1Cercospora 60, 1 94, 1 100, NA 100, NACladosporium 6, 3 13, 2 13, 2 59, 1Rhizopus 80, 1 85, 1 81, 1 90, 1Stachybotrys 100, NA 98, 1 100, NA 100, NAUnknown 20, 2 23, 2 6, 3 15, 3

Note: Presented as percentage of homes below detection limit, and median (CFU/m3) of those homes above detection limit.n = number of homes evaluated.NA, not applicable (no median, since all homes were below detection limits).

summer. The unknown fungal organisms had the highestconcentrations during fall and winter.

Table III shows the median coarse outdoor culturable fungalconcentrations. The highest concentrations during the springwere Cladosporium, during summer were of Stemphylium,during the fall were Stemphylium and Phoma, and duringwinter were unidentified fungi.

The data from Table IV illustrates the median fine in-door culturable fungal concentrations. Cladosporium had thehighest concentrations throughout various seasons comparedwith the other genera, with the exception of winter, whereAspergillus had the highest concentrations.

Table V contains the median outdoor fine culturable fun-gal concentrations. The highest concentrations were fromCladosporium across all seasons. More of the genera eval-uated in this study were present at concentrations above

the level of detection for the fine outdoor sampling cat-egory than any other category for the outdoor, fine par-ticle samples than for any of the other categories. Thefine outdoor sampling had 6%, 18%, and 38% more de-tection than fine inside, coarse inside, and coarse outside,respectively.

The overall findings of this study suggest that Cladosporiumdemonstrated the highest fungal concentrations comparedwith the other genera that were evaluated, specifically, thefall outdoor fine concentrations. The other evaluated genusthat appears predominantly in the samples was indoor fineAspergillus, with its highest concentrations during winter.Stemphylium has the second highest evaluated fungal concen-trations in the outdoor coarse-size range. Unknown genera, orthose concentrations that were not identified, were found in allsamples.

TABLE III. Coarse Outdoor Fungal Concentrations

Genus

Spring(n = 50)

(%, CFU/m3)

Summer(n = 48)

(%, CFU/m3)

Fall(n = 47)

(%, CFU/m3)

Winter(n = 39)

(%, CFU/m3)

Alternaria 22, 1 19, 2 6, 3 59, 2Bipolaris 86, 1 40, 2 17, 2 54, 1Stemphylium 98, 2 42, 6 4, 6 62, 2Phoma 8, 3 44, 1 4, 6 62, 2Aspergillus 42, 2 48, 1 64, 1 72, 1Cercospora 48, 1 85, 1 100, NA 100, NACladosporium 2, 6 4, 3 9, 4 33, 2Rhizopus 84, 1 79, 1 85, 1 95, 1Stachybotrys 100, NA 100, NA 100, NA 100, NAUnknown 2, 4 2, 3 2, 5 5, 5

Note: Presented as percentage of homes below detection limit, and median (CFU/m3) of those homes above detection limit.n = number of homes evaluated.NA, not applicable (no median, since all homes were below detection limits).

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TABLE IV. Fine Indoor Fungal Concentrations

Genus

Spring(n = 50)

(%, CFU/m3)

Summer(n = 48)

(%, CFU/m3)

Fall(n = 47)

(%, CFU/m3)

Winter(n = 39)

(%, CFU/m3)

Alternaria 28, 2 50, 3 51, 2 72, 1Bipolaris 88, 2 60, 2 21, 3 44, 3Stemphylium 96, 6 52, 5 23, 7 72, 2Phoma 14, 5 35, 1 23, 7 72, 2Aspergillus 0, 11 2, 17 0, 11 3, 13Cercospora 50, 1 94, 1 100, NA 100, NACladosporium 0, 29 0, 36 0, 61 8, 9Rhizopus 62, 1 48, 1 60, 1 69, 1Stachybotrys 88, 1 100, NA 100, NA 100, NAUnknown 4, 9 2, 9 2, 12 8, 10

Note: Presented as percentage of homes below detection limit, and median (CFU/m3) of those homes above detection limit.n = number of homes evaluated.NA, not applicable (no median, since all homes were below detection limits).

DISCUSSION

O ur literature search revealed few studies that weresimilar to this study. Some studies looked at fungal

bioaerosols. However, they often varied on one or more keymethodologies such as the type of building sampling, samplingdevice, collection media, detection limits, regional climate, etc.This makes it difficult to effectively compare concentrationsbetween studies; only general trends are compared in thisdiscussion.

Cooley et al.(23) did a study in the United States withinschools that were located along the Atlantic seaboard and theGulf of Mexico to correlate prevalence of certain fungi andsick building syndrome. The 48 schools that reported indoorair quality problems were examined over a period of 22 months,using a two-stage, Andersen air sampler with Sabouraud’s

Dextrose agar. The air sampling methodologies of Cooley et al.were similar to the authors’ study, with similar samplers used,but with different collection media. The study design differs,since that of Cooley et al. did not evaluate seasonal concen-trations among the different buildings and did not include thedifferent size-range relationship, nor were residential buildingsevaluated. The results from Cooley et al. also were similarto this study in that Cladosporium was reported in higherfungal concentrations, and the concentrations coincide with theconcentrations of fine indoor and outdoor samples during fall.

An assessment by Dacarro et al.(24) of the indoor microbialcontamination in scholastic sports environments was done.They used a gravity-settling culture method with potato dex-trose agar, malt extract agar, and DG18 as the collection media,which is very different from the sampling methodologies in thisstudy.(24) Three buildings with forced ventilation, six buildings

TABLE V. Fine Outdoor Fungal Concentrations

Genus

Spring(n = 50)

(%, CFU/m3)

Summer(n = 48)

(%, CFU/m3)

Fall(n = 47)

(%, CFU/m3)

Winter(n = 39)

(%, CFU/m3)

Alternaria 20, 3 29, 3 34, 2 46, 2Bipolaris 82, 1 50, 3 23, 4 51, 2Stemphylium 96, 5 50, 13 2, 10 56, 4Phoma 2, 4 42, 1 2, 10 56, 4Aspergillus 2, 6 2, 11 2, 8 10,12Cercospora 52, 2 96, 1 100, NA 100, NACladosporium 0, 33 0, 43 0, 112 8, 22Rhizopus 62, 1 75, 1 72, 1 69, 1Stachybotrys 88, 1 100, NA 100, NA 100, NAUnknown 0, 10 6, 9 0, 11 5, 14

Presented as percentage of homes below detection limit, and median (CFU/m3) of those homes above detection limit.n = number of homes evaluated.NA, not applicable (no median, since all homes were below detection limits).

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without forced ventilation, and two historical buildings inPavia, Italy, were assessed from December through October,which also greatly differs from the residential buildings eval-uated in this study. Outdoor samples taken from each buildingwere used as a control. The results of Dacarro et al. demonstratethat the mean fungal concentrations from historical buildings(458 CFU/m3) were higher than those from buildings withforced ventilation (156 CFU/m3) and from buildings withoutforced ventilation (348 CFU/m3). Cladosporium, Alternaria,and Penicillium were the most dominant during periods whenthe central heating was in use.

The fungal concentrations found in the study by Dacarroet al.(24) were at much higher levels than the concentrationsfound in this study. Dacarro et al. does not mention any seasonaleffect, although when the air samples were taken from thegyms they did note the operational status of ventilation orcentral heating. One could assume that months with ventilationrepresent summer months, those with ventilation off possiblywere spring, the ones with central heating on represent winterand the months when central heating was off were fall. Thestudy by Dacarro et al. does not include any repeated measure,unlike this study, where all samples across all seasons wererepeated and taken from the same house. The results from thisstudy in an arid climate differ greatly from those in the study byDacarro et al., which was done in a humid climate and founda lower concentration of total culturable fungal organisms.

An investigation was made in the Cincinnati, Ohio, areawhere six homes were sampled across three seasons todetermine culturability of airborne fungi collected in indoorand outdoor air samples.(25) Researchers conducted a long-term sampling, over a 24-hr period, using a Button PersonalInhalable Aerosol sampler with polycarbonate filters, whichwas then cultured onto MEA. No samples were taken insummer, since it was assumed that the fungal concentrationswere similar to those of late spring.

The median fungal concentrations for indoor and out-door samples throughout the year were 89 CFU/m3 and168 CFU/m3, respectively. The median fungal concentrationsfound by Lee et al.(25) for indoor and outdoor samples weresimilar to those found in samples collected in this study, insummer and fall, for fine indoor and outdoor concentrations.However, both studies use very different methodologies.The results given in the study by Lee et al. combine theinformation of the three seasons, diminishing the ability todetect any seasonality impact that might be present in the fungalconcentrations. Their study and this investigation agree on thebasis that fungal organisms and concentrations will vary withrespect to differences in climate characteristics and vegetation.

Shelton et al.(19) looked at buildings with reported indoor airquality (IAQ) issues and, as a result, their study found higherconcentrations of fungal organisms within their southwesternsamples than did this study. Their methods used the AndersenN6 sampler with the culture media of either Rose Bengalagar or MEA. Shelton et al. also found Cladosporium tobe a prevalent organism in the southwestern samples (mean,130 CFU/m3). However, it differs from the authors’ study

by identifying the highest total fungal concentrations inthe summer, rather than in the fall. Again, this may beattributed to the nonrandom sample with IAQ issues tested byShelton et al.

The houses in this study had no history of IAQ issuesor fungal contamination; therefore, the total fungal concen-trations and individual organism concentrations were lowerthan, and not as diverse as, those recovered in the study byShelton et al., which examined buildings with IAQ issues. Inthe study by Shelton et al. and in other studies, a significantpresence of Penicillium concentrations was observed in variousseasons. In the authors’ study, no Penicillium was identified.However, Penicillium was not one of the nine genera selectedfor evaluation in their study. It is very likely that Penicilliumcomprised a portion of the organisms grouped into the authors’“Unknown” category. This difference between the presentstudy and the others is a limitation to comparing all organismsfrom different regions.

Horner et al.(26) conducted a study similar to this one, buttheir results were not separated by size, and they evaluatedmultiple locations within the houses. They evaluated thefungal bioaerosol content of 50 non-water-damaged homesin Georgia, in winter and in summer, using the SAS HighFlow air sampler collected onto MEA. Their results showedhigher total concentrations in summer than in winter, withlimited seasonal variability of the ranking by abundance andprevalence of airborne fungi genera.

The present study of an arid climate showed that thehighest concentration was recovered during fall, with seasonalvariability. These results further differed from the study byHorner et al. in that they recovered at least twice the numberof organisms from their indoor and outdoor samples as theauthors did in their samples. This is unexpected, since theirstudy used the SAS sampler.

The SAS sampler has been shown to have a lower over-all collection efficiency than the Andersen-type, six-stageimpactor, which is comparable to the two-stage, ambient,culturable sampler system used in this study. Therefore, onewould expect to find a lower concentration of organisms fromthe SAS sampler if it were operated side by side with the two-stage, ambient, culturable sampler system.(27) This differenceimplies that the recovery differences between the authors’ ElPaso samples and those of Horner et al. in Georgia are evengreater, due to the differences in sampler recovery efficiencies.This could be a result of sampling methodologies and theanalysis of data or a regional difference. It is likely that theclimate in Georgia is more supportive of fungal growth thanthe arid, high UV climate of El Paso. However, both studiesidentified Cladosporium as a dominant organism.

Sterling and Lewis(28) conducted a study that involved airsampling of fungal spore concentration inside and outsideoccupied mobile homes (n = 8 in spring; n = 10 in summer)in the El Paso region. The results of that study differedslightly from those of the present study. Sterling and Lewisfound similar fungal concentrations indoors in both seasons(spring = 36.2 counts/m3; summer = 37.7 counts/m3). The

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outdoor fungal concentrations were different, with most beingrecovered in the spring (spring = 85.6 counts/m3; summer =59.7 counts/m3).

The present study recovered more culturable fungal organ-isms (Table I) in the summer than in the spring sampling. Theresults of the Sterling and Lewis study were not size delineated,since the RotoRod sampler was used. Combining the fine andcoarse portions of the present study samples shows that a largernumber of indoor and outdoor organisms was recovered thanin the Sterling and Lewis study. This is counterintuitive, sinceone would expect that culture methods would recover fewerorganisms than non-culture-based methodology. This could bea result of the sampling efficiency of the RotoRod sampler,which was discussed in the article by Sterling and Lewis. TheRotoRod sampler was shown to be very inefficient for particlesless than 10 µm in the study by Adhikari et al. of fungal sporesin which the concentration of total fungal spores averaged lessthan half of another simultaneously operated filter sampler.(29)

The fine fraction in the present study was always higherthan the coarse fraction and averaged 85% of the total colonyforming units. The coarse portion of the sample would be mostcomparable to that in the Sterling and Lewis article. In thepresent study, fewer organisms were recovered in the coarse-particle fraction than were found by Sterling and Lewis.

The concentration (CFU/m3) of organisms recovered fromthe fine-size range was 12 times and 6 times greater thanthose from the coarse-size range for indoor and outdoorsamples, respectively, so the concentration from the fine-size range accounted for the majority of fungal organisms.The concentration ratio of fine to coarse organisms insideresidences in the authors’ study was nearly twice that of theoutdoor ones, across seasons. This is most likely because ofthe greater coarse fungal organisms recovered outdoors thanindoors, due probably to the aerosolization of the particles. Theindoor environment lacks the wind speed found in the outdoorenvironment that is required to aerosolize and maintain aloftthe larger coarse fungal organisms.

The fine outdoor samples also had more genera recoveredabove the level of detection than the other samples. The outdoorenvironment has greater wind exposure and greater fungalsources, which are probable reasons for the greater prevalenceof detectable genera in the fine outdoor samples. Because thefine portion of fungal organisms is able to penetrate deeper intothe respirator system and is much more prevalent in the indoorenvironment, it might be beneficial to focus more attention onthe fine portion of fungal organisms in the indoor environment.

Arid environments potentially exhibit different fungal or-ganisms and concentrations compared with those environ-ments where the humidity is at high levels, having a greatervegetation index and a higher content of moisture in the air.Seasons accentuate these differences, especially in the areaswhere each season is unique and has distinct environmentalconditions. Reporting the annual mean fungal concentrationscould be an underestimate of the actual concentrations com-pared with the seasonal concentrations, since fungal concentra-tions fluctuate with respect to seasonality, demonstrating low

concentrations in some seasons and very high concentrationsin others.

This study was able to detect seasonal differences betweendifferent culturable fungal taxa across different size ranges. Allfungal concentrations were statistically different throughoutthe year, with the exception of coarse indoor fungal con-centrations. The highest concentrations were found duringfall in the outdoor fine-size range. The lowest concentrationswere the indoor coarse concentrations during spring. From thisstudy it can be concluded that Cladosporium had its highestconcentrations during fall in the arid environment studied, andwas the predominant genera. The data in the study suggestseasonal differences between different culturable fungal taxaacross different size ranges.

In addition, it shows that the concentration ratio of fine tocoarse organisms inside the residences was nearly twice that ofthe outdoors, across seasons. Future studies may want to evalu-ate further the fine concentration of organisms, as they are ableto penetrate deeper into the respiratory tract and compromisedthe majority of the indoor organisms, which is where peoplespend most of their time. From this study it can be concludedthat seasonality plays a role in culturable fungal concentrations,where temperature and relative humidity differences affectthe dispersal and behavior of fungal concentrations. This willprovide a better understanding of how fungal concentrationsmay impact human health as it varies with seasons.

ACKNOWLEDGMENTS

T he authors acknowledge the contributions of AngelinaGandara and Alejandro Gutierrez at The University of

Texas at El Paso, and Fernanda Payan and Carla Alvarado at theUniversity of Texas School of Public Health. Editorial supportwas provided by Susan Navarro and the Hispanic Health Dis-parities Research Center (P20 MD000548-01 NIH/NCMHD).This research was partially funded by Hot Projects, an initiativeof the Paso del Norte Health Foundation, and Center of En-vironmental Resource Management Environmental ProtectionAgency Student Support Program at The University of Texasat El Paso.

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