First report of Legionella pneumophila in car cabin air filters. Are these a potential exposure pathway for professional drivers?

Legionella pneumophila: The Journey from the Environment to the Blood

An outbreak of a potentially fatal form of pneumonia in 1976 and in the annual convention of the American Legion was the first time that Legionella spp. was identified. Thereafter, the term Legionnaires’ disease (LD) was established. The infection in humans is transmitted by the inhalation of aerosols that contain the microorganisms that belong to the Legionellaceae family and the genus Legionella. The genus Legionella contains genetically heterogeneous species and serogroups. The Legionella pneumophila serogroup 1 (Lp1) is the most often detected strain in outbreaks of LD. The pathogenesis of LD infection initiates with the attachment of the bacterial cells to the host cells, and subsequent intracellular replication. Following invasion, Legionella spp. activates its virulence mechanisms: generation of specific compartments of Legionella-containing vacuole (LCV), and expression of genes that encode a type IV secretion system (T4SS) for the translocation of proteins. The ability of L. pneumophila to transmigrate across the lung’s epithelium barrier leads to bacteremia, spread, and invasion of many organs with subsequent manifestations, complications, and septic shock. The clinical manifestations of LD depend on the bacterial load in the aerosol, the virulence factors, and the immune status of the patient. The infection has two distinct forms: the non- pneumatic form or Pontiac fever, which is a milder febrile flu-like illness, and LD, a more severe form, which includes pneumonia. In addition, the extrapulmonary involvement of LD can include heart, brain, abdomen, and joints.

Antimicrobial effects of automobile screenwashes against Legionella pneumophila

AIMS

Legionella pneumophila (Lp), a human pathogen, has been detected in windscreen wiper fluid reservoirs (WWFRs) where commercial screenwashes (CSWs) are commonly added. Limited information is available on CSWs against planktonic Lp; however, responses of sessile Lp and planktonic Lp pre-acclimated in nutrient-limited water to CSWs remain unknown. This study thus investigates the antibacterial effects of CSWs on sessile and starved planktonic Lp, in comparison with unstarved Lp.

METHODS AND RESULTS

Lp biofilms were produced on glass and WWFR materials of high-density polyethylene (HDPE) and polypropylene (PP). Planktonic Lp with and without acclimation in tap water were prepared. Log reductions in cell counts averaged 0.4-5.0 for ten brands of CSWs against sessile Lp and 1.0-3.9 and 0.9-4.9, respectively, against starved and unstarved planktonic Lp for five CSWs. Both biofilm formation and acclimation in tap water enhanced Lp resistance to CSWs. Significantly different log-reduction values among CSW brands were observed for sessile Lp on HDPE and planktonic Lp regardless of acclimation (p<0.05).

CONCLUSIONS

Biofilm formation, starvation acclimation, and CSW brand are crucial factors influencing Lp response to CSWs.

SIGNIFICANCE AND IMPACT OF STUDY

This study advances the knowledge of Lp reaction in anthropogenic water systems with CSWs.

Legionella and Air Transport: A Study of Environmental Contamination

Introduction: There is growing interest in the public health and transport sectors in research into exposure to biological hazards, considering not only the risks arising from inter-human contagion, but also those related to exposure to the flight environment itself. The aim of this paper is to report data from an investigation into the water and air-conditioning systems of commercial aircraft for the presence of Legionella contamination, with a total of 645 water samples taken during the period 2007−2021. Methods: The investigation involved 126 aircraft of six different commercial aircraft types: MD80, Airbus A320 F, Embraer 175/190, AIRBUS A330, Boeing 767 and Boeing 777. Water samples were taken from the water systems (toilet taps, galley and boilers). Each sample was preliminarily subjected to an evaluation of the following parameters: temperature, pH and residual chlorine. The ScanVit® Legionella kit was used for bacteria detection and enumeration. Results: Samples were considered positive if the number of colony-forming units/liter (CFU/L) was >100. For the entire observation period, 45% of the investigated aircraft tested positive. Regarding the overall number of samples analyzed, 68.4% (441/645) were below 100 CFU/L, and thus within the limits allowed by the Italian Guidelines. Conclusions: Water system contamination with Legionella in the air transport field is a real public health issue that should not be underestimated given the heavy passenger traffic. Infection should be considered an occupational risk to which crew members are exposed.

Epidemiology of Legionnaires' Disease, Hong Kong, China, 2005-2015

We reviewed findings of clinical, epidemiologic, and environmental investigations for 288 confirmed case-patients with Legionnaires’ disease reported in Hong Kong, China, during January 2005−December 2015. We found that chronic renal failure/impairment (adjusted odds ratio [aOR] 4.09), chronic pulmonary diseases (aOR 3.22), malignancy (aOR 3.04), and heart diseases (aOR 2.15) were independently associated with a higher risk for severe Legionnaires’ disease. However, patients with hyperlipidemia had a lower risk for severe outcome (aOR 0.17). Legionella positivity rate was 22% for 1,904 water samples collected. We found a higher positivity rate in summer months (28%−30%), which corroborated with months of highest rainfalls. Our novel finding that Legionnaires’ disease patients with hyperlipidemia had a lower risk for severe outcome deserves further study to confirm the observation and ascertain the underlying reason.

Solar and Climate Effects Explain the Wide Variation in Legionellosis Incidence Rates in the United States

Legionellosis, an infection caused by the environmental bacteria Legionella spp., has become a significant public health problem in the United States in recent years; however, among the states, the incidence rates vary widely without a clear explanation. This study examined environmental effects on the 2014-to-2016 average annual legionellosis incidence rates in the U.S. states through correlative analyses with long-term precipitation, temperature, solar UV radiation, and sunshine hours. The continental states west of ∼95°W showed low incidence rates of 0.51 to 1.20 cases per 100,000 population, which corresponded to low precipitation, below 750 mm annually. For the eastern states, where precipitation was higher, solar effects were prominent and mixed, leading to wide incidence variation. Robust regressions suggested a dividing line at 40°N: north of this line, rising temperature, mainly from solar heat, raised legionellosis incidence to a peak of 4.25/100,000 in Ohio; south of the line, intensifying sunlight in terms of high UV indices and long sunshine hours prevailed to limit incidence gradually to 0.99/100,000 in Louisiana. On or near the 40°N line were 15 eastern states that had leading legionellosis incidence rates of >2.0/100,000. These states all showed modest environmental parameters. In contrast, the frigid climate in Alaska and the strong year-round solar UV in Hawaii explained the lowest U.S. incidences, 0.14/100,000 and 0.47/100,000, respectively, in these states. The findings of solar and climate effects explain the wide variation of legionellosis incidence rates in the United States and may offer insights into the potential exposure to and prevention of infection.IMPORTANCE Legionellosis, caused by the environmental bacteria Legionella spp., has become a significant public health problem in the United States in recent years, with ∼6,000 cases annually. The present study showed, through a series of correlative analyses with long-term precipitation, temperature, solar UV radiation, and sunshine hours, that these environmental conditions strongly influence the legionellosis incidence rates across the United States in mixed and dynamic fashions. The incidence rates varied remarkably by region, with the highest in Ohio and New York and the lowest in Alaska. A precipitation threshold above 750 mm was required for elevated legionellosis activity. Regression models and dividing lines between regions were established to show the promotive effect of temperature, as well as the inhibitive effects of solar UV and sunshine hours. These findings explain the wide variation of legionellosis incidence rates in the United States. They may also offer insights into potential exposure to and prevention of infection.

Airborne Pathogens inside Automobiles for Domestic Use: Assessing In-Car Air Decontamination Devices Using Staphylococcus aureus as the Challenge Bacterium

Family cars represent ∼74% of the yearly global output of motorized vehicles. With a life expectancy of ∼8 decades in many countries, the average person spends >100 min daily inside the confined and often shared space of the car, with exposure to a mix of potentially harmful microbes. Can commercial in-car microbial air decontamination devices mitigate the risk? Three such devices (designated devices 1 to 3) with HEPA filters were tested in the modified passenger cabin (3.25 m³) of a four-door sedan housed within a biosafety level 3 containment facility. Staphylococcus aureus (ATCC 6538) was suspended in a soil load to simulate the presence of body fluids and aerosolized into the car's cabin with a 6-jet Collison nebulizer. A muffin fan (80 mm by 80 mm, with an output of 0.17 m³/min) circulated the air inside. Plates (150 mm diameter) of Trypticase soy agar (TSA), placed inside a programmable slit-to-agar sampler, were held at 36 ± 1°C for 18 to 24 h and examined for CFU. The input dose of the test bacterium, its rate of biological decay, and the log₁₀ reductions by the test devices were analyzed. The arbitrarily set performance criterion was the time in hours a device took for a 3-log₁₀ reduction in the level of airborne challenge bacterium. On average, the level of S. aureus challenge in the air varied between 4.2 log₁₀ CFU/m³ and 5.5 log₁₀ CFU/m³, and its rate of biological decay was -0.0213 ± 0.0021 log₁₀ CFU/m³/min. Devices 1 to 3 took 2.3, 1.5, and 9.7 h, respectively, to meet the performance criterion. While the experimental setup was tested using S. aureus as an archetypical airborne pathogen, it can be readily adapted to test other types of pathogens and technologies.IMPORTANCE This study was designed to test the survival of airborne pathogens in the confined and shared space of a family automobile as well as to assess claims of devices marketed for in-car air decontamination. The basic experimental setup and the test protocols reported are versatile enough for work with all major types of airborne human pathogens and for testing a wide variety of air decontamination technologies. This study could also lay the foundation for a standardized test protocol for use by device makers as well as regulators for the registration of such devices.

Airborne Infectious Agents and Other Pollutants in Automobiles for Domestic Use: Potential Health Impacts and Approaches to Risk Mitigation

The world total of passenger cars is expected to go from the current one billion to >2.5 billion by 2050. Cars for domestic use account for ~74% of the world's yearly production of motorized vehicles. In North America, ~80% of the commuters use their own car with another 5.6% travelling as passengers. With the current life-expectancy of 78.6 years, the average North American spends 4.3 years driving a car! This equates to driving 101 minutes/day with a lifetime driving distance of nearly 1.3 million km inside the confined and often shared space of the car with exposure to a mix of potentially harmful pathogens, allergens, endotoxins, particulates, and volatile organics. Such risks may increase in proportion to the unprecedented upsurge in the numbers of family cars globally. Though new technologies may reduce the levels of air pollution from car exhausts and other sources, they are unlikely to impact our in-car exposure to pathogens. Can commercial in-car air decontamination devices reduce the risk from airborne infections and other pollutants? We lack scientifically rigorous protocols to verify the claims of such devices. Here we discuss the essentials of a customized aerobiology facility and test protocols to assess such devices under field-relevant conditions.

Automobile windshield washer fluid: A potential source of transmission for Legionella

Epidemiological evidence suggesting driving cars to be a risk factor for legionellosis has prompted public health studies to investigate vehicle windshield washer fluid as a novel transmission source of this disease. The goal of the current study was to investigate whether or not windshield washer fluid could serve as a potential source of transmission for Legionella. A wide variation in the survival of L. pneumophila was observed when incubated in different washer fluids at 25 and 37 °C, however, one brand tested supported Legionella survival similar to or greater than sterilized deionized water. In addition, 1 L of tap water contained in a washer fluid reservoir was able to support population growth and survival of Legionella for several months. In a field study examining the windshield washer fluid of 12 elementary school buses, Legionella were detected from 84% of samples at a high concentration of 8.1×10(4) CFU/mL. Culturable cells were also detected in aerosolized washer fluid during washer fluid spray. By demonstrating survival in certain windshield washer fluids, growth within washer fluid reservoirs, and the presence of viable cells in bus washer fluid spray, we have provided evidence suggesting the potential for a novel route of Legionella exposure.

Confirmed and Potential Sources of Legionella Reviewed

Legionella bacteria are ubiquitous in natural matrices and man-made systems. However, it is not always clear if these reservoirs can act as source of infection resulting in cases of Legionnaires' disease. This review provides an overview of reservoirs of Legionella reported in the literature, other than drinking water distribution systems. Levels of evidence were developed to discriminate between potential and confirmed sources of Legionella. A total of 17 systems and matrices could be classified as confirmed sources of Legionella. Many other man-made systems or natural matrices were not classified as a confirmed source, since either no patients were linked to these reservoirs or the supporting evidence was weak. However, these systems or matrices could play an important role in the transmission of infectious Legionella bacteria; they might not yet be considered in source investigations, resulting in an underestimation of their importance. To optimize source investigations it is important to have knowledge about all the (potential) sources of Legionella. Further research is needed to unravel what the contribution is of each confirmed source, and possibly also potential sources, to the LD disease burden.