Seasonal variability of culturable fungal genera in the house dust of inner-city residences

Fungal populations in the bedroom dust of children in Havana, Cuba, and its relationship with environmental conditions

The study of the fungal community composition in house dust is useful to assess the accumulative exposure to fungi in indoor environments. The objective of this research was to characterize the fungal diversity of house dust and its association with the environmental conditions of bedrooms. For this, the dust was collected from 41 bedrooms of children between the ages of 8 and 9 with a family history of asthma, residents of Havana, Cuba. The fungal content of each sample was determined by two methods: plate culture with malt extract agar and by direct microscopy. An ecological analysis was carried out from the fungal diversity detected. To describe the factors associated with the fungi detected, bivariate logistic regression was used. Through direct microscopy, between 10 and 2311 fragments of hyphae and spores corresponding mainly to Cladosporium, Coprinus, Curvularia, Aspergillus/Penicillium, Xylariaceae, and Periconia were identified. Through the culture, 0-208 CFU were quantified, where Aspergillus, Cladosporium, and Penicillium predominated. The culturability evidenced the differences between the quantification determined by both methods. A positive relationship was found between the type of cleaning of the furniture, the presence of trees in front of the bedroom, indoor relative humidity, indoor temperature, the presence of air conditioning, and natural ventilation with specific spore types and genera. The use of two different identification methods allowed to detect a greater fungal diversity in the residences evaluated. Monitoring the exposure to these fungal allergens in childhood can help to prevent sensitization in the allergic child, the development of asthma, and other respiratory diseases.

Residential airborne culturable fungi under general living scenario: On-site investigation in 12 typical cities, China

BACKGROUND

Residential airborne fungi may present obvious risk to human health. However, many countries do not recognize the necessarily need to control residential airborne culturable fungi (RAF). In China, few systemic investigations have been conducted to illustrate the distribution of residential airborne fungi and identify the association between indoor influencing variables and RAF under general living scenario in China.

OBJECTIVE

This study aimed to investigate RAF with the on-site research of 12 typical cities in China, and provided the latest characteristics and potential influencing factors of RAF under general living scenario.

METHODS

We measured RAF and investigated residential characteristics in 12 typical cities in China, 2018. At least 50 resident families were randomly selected both from downwind and upwind districts in each city with pre-proposed requirements. The RAF were sampled by the six-stage Anderson impactor. PM_2.5 and PM₁₀ were monitored by calibrated light-scattering dust meters. CO and CO₂ were monitored by non-dispersive infrared analyzer method. NO₂ was determined by Saltzman method. General linear model was used to evaluate the association between RAF exposure and residential characteristics with adjustment for potential confounders.

RESULTS

The RAF concentrations ranged from 0 to 9371 CFU/m³ with a median concentration of 396 CFU/m³. The median concentrations of RAF in the warm season were statistically higher than the cold season in Panjin, Qingdao, Lanzhou and Luoyang, but lower than the cold season in Shijiazhuang, Ningbo and Nanning. RAF in the bedrooms were more than the living rooms in all cities except Xi'an. Temperature and humidity had an interactive effect on the RAF (OR = 1.0006, 95% CI: 1.0005, 1.0006). Some residential environmental pollutants, including PM_2.5 (OR = 0.9989, 95% CI: 0.9988, 0.9989), PM₁₀ (OR = 0.9993, 95% CI: 0.9993, 0.9993), and CO₂ (OR = 0.0236, 95% CI: 0.0230, 0.0243), were negatively correlated with RAF. CO (OR = 1.1450, 95% CI: 1.1433, 1.1467) and NO₂ (OR = 1.0026, 95% CI: 1.0024, 1.0028) were positively correlated with RAF. Architectural characteristics (sunlight exposure, building history, longitude, latitude, total living area, living floor, distance from the road, house type, the layers of window glass and decoration), family-related information (income) and lifestyle behaviors (keeping pets, growing plants, cooking, using insecticide, burning incense, heating, using air conditioner and cleaning frequencies) were also significantly related with RAF.

CONCLUSIONS

This study reported nation-wide baseline condition of RAF and related influencing factors under general living scenario with quantitative details, which are exceedingly promising for evidence-driven standard and reasonable control strategy of residential airborne culturable in China.

Indoor fungal diversity and asthma: a meta-analysis and systematic review of risk factors

BACKGROUND

Indoor dampness increases the risk of indoor fungal growth. A complex interaction between occupant behaviors and the built environment are thought to affect indoor fungal concentrations and species diversity, which are believed to increase the risk of having asthma, exacerbation of asthma symptoms, or both. To date, no systematic review has investigated this relationship.

OBJECTIVE

This review aims to assess the relationship between exposure to indoor fungi identified to the genera or species level on asthma outcomes in children and adults.

METHODS

Ten databases were systematically searched on April 18, 2013, and limited to articles published since 1990. Reference lists were independently screened by 2 reviewers, and authors were contacted to identify relevant articles. Data were extracted from included studies meeting our eligibility criteria by 2 reviewers and quality assessed by using the Newcastle-Ottawa scale designed for assessment of case-control and cohort studies.

RESULTS

Cladosporium, Alternaria, Aspergillus, and Penicillium species were found to be present in higher concentrations in homes of asthmatic participants. Exposure to Penicillium, Aspergillus, and Cladosporium species were found to be associated with increased risk of reporting asthma symptoms by a limited number of studies. The presence of Cladosporium, Alternaria, Aspergillus, and Penicillium species increased the exacerbation of current asthma symptoms by 36% to 48% compared with those exposed to lower concentrations of these fungi, as shown by using random-effect estimates. Studies were of medium quality and showed medium-high heterogeneity, but evidence concerning the specific role of fungal species was limited.

CONCLUSION

Longitudinal studies assessing increased exposure to indoor fungi before the development of asthma symptoms suggests that Penicillium, Aspergillus, and Cladosporium species pose a respiratory health risk in susceptible populations. Increased exacerbation of current asthma symptoms in children and adults were associated with increased levels of Penicillium, Aspergillus, Cladosporium, and Alternaria species, although further work should consider the role of fungal diversity and increased exposure to other fungal species.

Mold management of wetted carpet

This study evaluated the growth and removal of fungi on wetted carpet using newly designed technologies that rely on physical principles of steam, heat, and fluid flow. Sixty samples of carpet were embedded with heat-treated house dust, followed by embedding, wearing with a hexapod, and wetting. Samples were inoculated using a liquid suspension of Cladosporium sphaerospermum prior to placement over a water-saturated foam pad. Incubation times were 24 hr, 7 days, and 30 days. Cleaning was performed using three methods; high-flow hot water extraction, hot water and detergent, and steam. Fungal loading increased from approximately 1500 colony forming units per area (CFU/cm(2)) in 24 hr to a maximum of approximately 10,200 CFU/cm(2) after 7 days with a slight decline to 9700 CFU/cm(2) after 30 days incubation. Statistically significant differences were found among all three methods for removal of fungi for all three time periods (p < 0.05). Steam-vapor was significantly better than the alternative methods (p <0.001) with over 99% efficiency in mold spore decline from wetted carpet after 24 hr and 30 days, and over 92% efficiency after 7 days. The alternative methods exhibited lower efficiencies with a decline over time, from a maximum of 82% and 81% at 24 hr down to 60% and 43% at 30 days for detergent-hot water and high-flow, hot water extraction, respectively. The net effect of the mold management study demonstrates that while steam has a consistent fungal removal rate, the detergent and high-flow, hot water methods decline in efficiency with increasing incubation time.

Assessing allergenic fungi in house dust by floor wipe sampling and quantitative PCR

In the present study, we modified an existing surface wipe sampling method for lead and other heavy metals to create a protocol to collect fungi in floor dust followed by real-time quantitative PCR (qPCR)-based detection. We desired minimal inconvenience for participants in residential indoor environmental quality and health studies. Accuracy, precision, and method detection limits (MDLs) were investigated. Overall, MDLs ranged from 0.6 to 25 cell/cm² on sampled floors. Overall measurement precisions expressed as the coefficient of variation because of sample processing and qPCR ranged 6-63%. Median and maximum fungal concentrations in house dust in study homes in Visalia, Tulare County, California, were 110 and 2500 cell/cm², respectively, with universal fungal primers (allergenic and nonallergenic species). The field study indicated samplings in multiple seasons were necessary to characterize representative whole-year fungal concentrations in residential microenvironments. This was because significant temporal variations were observed within study homes. Combined field and laboratory results suggested this modified new wipe sampling method, in conjunction with growth-independent qPCR, shows potential to improve human exposure and health studies for fungal pathogens and allergens in dust in homes of susceptible, vulnerable population subgroups.

PRACTICAL IMPLICATIONS

Fungi are ubiquitous in indoor and outdoor environments, and many fungi are known to cause allergic reactions and exacerbate asthma attacks. This study established--by modifying an existing--a wipe sampling method to collect fungi in floor dust followed by real-time quantitative PCR (qPCR)-based detection methodologies. Results from this combined laboratory and field assessment suggested the methodology's potential to inform larger human exposure studies for fungal pathogens and allergens in house dust as well as epidemiologic studies of children with asthma and older adults with chronic respiratory diseases.