Microbial Life in the Wake of Hurricanes

Nov. 16, 2018

The 2018 Atlantic hurricane season officially concludes at the end of November, but many are still grappling with devastation caused by the high wind speeds, intense rainfall, and massive storm surges of this year’s tropical storms. According to reports by CNBC and Fortune, this season’s two Category 4 hurricanes, Florence and Michael, are responsible for an estimated $27 billion in damage to regions of the Southeastern United States. Economic damage of this magnitude often overshadows the fact that natural disasters have very real consequences for microbial ecosystems, but research shows that the environmental impacts of hurricanes go far beyond what the eye can see.
NOAA satellite image of Hurricane Florence. Source.
Source: NOAA

How Have Recent Tropical Storms Influenced Local Microbial Ecosystems?

Tropical storms have major urban repercussions, leading to sewage-related issues and mold growth. Subsequent spread of disease and infection may further threaten communities struck by hurricanes.

Urban Repercussions

Hurricane force winds shred buildings, uproot trees, and rip through power lines. Resultant power outages disrupt local biofilms and filtration systems, releasing various gram-negative organisms and waterborne pathogens into the environment. Heavy rainfall leads to significant flooding, and as wind and rain subside, floodwaters become stagnant. According to the Center for Disease Control and Prevention (CDC), stagnant floodwaters can become dangerous breeding grounds for pathogenic microbial life and vectors of disease.

Aerial photo of flooding caused by Hurricane Florence.
Source: South Carolina National Guard.
 
To learn more about the pathogenic bacteria lurking in urban, hurricane floodwaters, Lauren Stadler and colleagues from the University of Texas at San Antonio took samples from the floodwater on Houston streets, inside homes, in bayous, and in the sediments left by receding floodwaters of Hurricane Harvey in 2017. The highest levels of fecal bacteria and human pathogens (Vibrio and Legionella) were discovered inside homes that contained stagnant floodwater. This means that individuals attempting to live in homes with standing water are likely at the greatest risk of exposure to disease and infection following a hurricane. Therefore, elimination of standing water inside of homes and/or evacuation of at-risk individuals is of great importance as cities rebuild and recover.

Sewage Contamination

Significant flooding often causes sewage overflows and storm run-offs that further contaminate rivers, bays, canals, and city streets, increase the risk of disease, and trigger algae blooms that can be dangerous to marine life. Floodwaters in Houston, Tex., were polluted by more than 2 million pounds of fecal contamination when 800 wastewater treatment plants reported spills due to flooding from Hurricane Harvey in 2017. Following Hurricane Sandy in 2012, 8 states reported a total of nearly 11 billion gallons of untreated or partially treated sewage overflow, and millions of gallons of sewage were spread in Hurricane Irma’s wake.

Unsurprisingly, raw sewage contains many species of fecal bacteria that may be harmful to humans, including Escherichia coli, Salmonella enterica and Clostridium perfringens. The impact? Regional drinking water quality deteriorates dramatically, leading to disease outbreaks of mild to severe gastrointestinal infection, as well as incidences of gas gangrene and necrotizing fasciitis.

Mold Growth

Even after the floodwaters recede, conditions associated with lingering heat and moisture are ideal for mold spores to flourish. Following Hurricane Katrina, approximately 194,000 homes in flooded areas showed visible mold growth. The greater the flood damage, the more susceptible a home becomes to the development of mold. Possible sources include Alternaria, Aspergillus, Cladosporium, Curvularia and Penicillium. Untreated mold may cause significant property damage and inhalation of mold spores may cause negative health implications of varying degrees. Immunocompromised individuals are most susceptible to invasive fungal infections, however even healthy people may experience symptoms ranging from mild irritation to more severe allergic reactions (asthma, wheezing, stuffy nose or skin irritation).

Once again we are reminded of the danger of attempting to live inside homes with standing water. The CDC recommends cleaning and drying out a building within 24-48 hours in order to prevent mold growth. However, they also offer instructions for cleaning minor mold damage and a recommendation to seek professional help for damage that covers more than 10 square feet.

How Have Recent Tropical Storms Influenced Airborne Microbial Ecosystems?

Hurricane winds lift new microbes from the Earth’s surface high into the atmosphere. Evidence suggests that storms directly influence the types of bacteria lifted as they pass over terrestrial and aquatic ecosystems.

Atmospheric Microbes

Together, the collection of gasses surrounding our planet is known as the atmosphere. Earth’s atmosphere is divided into a series of layers, each with its own characteristic features. Many small liquid and solid particles (aerosols), including dust, pollen, sea salt, volcanic ash, and other man-made pollutants make their way into the atmosphere every year. Studies have identified robust baseline populations of bacteria living among these particles high above the surface of the Earth.
Layers of Earth's atmosphere.
Source: Wikimedia Commons

Recently, the National Aeronautics and Space Administration (NASA) counted an average of 5,100 bacterial cells per cubic meter in samples of air collected from regions of the atmosphere 8-15 km above the Earth’s surface (troposphere). These microbes originate from various terrestrial and aquatic sources (soil, oceans, plants, animals, wastewater treatment plants,etc.) Evidence suggests that aerosolized bacteria may feed off of clouds and form active atmospheric ecosystems. But how do these bugs make their way up there in the first place? Many hitch rides on jetstreams or are carried aloft by other types of strong winds. This knowledge is what led researchers to question the impact of hurricane force winds on airborne microbial communities.

Hurricane Contributions

The births of 2 major hurricanes in 2010 provided researchers from NASA the opportunity to take microbial research to new heights. Hurricanes Earl and Karl, struck coastal territory along the Caribbean Sea and the midwestern Atlantic Ocean from August 10, 2010-September 20, 2010. During this 6-week period, the Genesis and Rapid Intensification Process (GRIP) campaign conducted regional and intercontinental flights across the United States to capture air mass samples from portions of the troposphere. Samples were taken before, after, and during various active phases of the hurricanes. Concentrations of bacterial and fungal cells in each sample were then measured using molecular and microscopic techniques.

Comparison of samples taken in stormy and non-stormy climates revealed that hurricanes have a definite effect on the composition of bacterial communities in the atmosphere. 314 different families of bacteria were identified in the air samples that GRIP collected. Certain core organisms were present regardless of climate or geography change. However, hurricane samples contained a wide variety of new cells and taxa that were not present in control samples (non-stormy climates). The conclusion? Powerful hurricane force winds propel new microbes from the Earth’s surface into the atmosphere.

Furthermore, the terrain over which a storm passes influences the kind of bacteria that are aerosolized. Bacteria associated with human and animal feces, such as Escherichia and Streptococcus, were only present in hurricane samples, indicating that bacteria associated with sewage overflows on the Earth’s surface were lifted by hurricane winds passing over contaminated areas. Unfortunately, the type of genetic analysis that GRIP used did not allow for accurate identification of organisms at the species level. Therefore, no definitive claims were made about the pathogenicity of the fecal bacteria that were cataloged. Regardless, this research greatly advanced our understanding of the powerful impact that hurricanes have on airborne microbial ecosystems.

In the wakes of Hurricanes Florence and Michael, affected communities are striving to rebuild and recover. Based on historical patterns and scientific findings, microbial ecosystems both on and above the Earth are currently attempting to do the same. The environmental impacts of recent storms have altered microbial ecosystems in and around floodwaters, inside and outside of homes, sewage treatment facilities, and the atmosphere. However, much like people, microbes are dynamic and resilient. In time, most will return to pre-storm levels. In well-developed countries, the numbers of elevated microbes in urban areas begin to subside as soon as floodwaters are eliminated. Research shows that many microbial populations gradually decrease to pre-storm levels within 2-3 months after the storm. Other sources suggest that recovery takes much longer. As a general rule, the National Academy of Science has estimated that total reconstruction takes 10 times as long as the initial emergency period of a natural disaster. Until then, being well-informed about the microscopic repercussions of tropical storms will better equip us to restore our communities today and protect them when the next hurricane strikes.
 

Author: Ashley Hagen, M.S.

Ashley Hagen, M.S.
Ashley Hagen is a science communications specialist at ASM.