Cold Spots in Neonatal Incubators Are Hot Spots for Microbial Contamination

Abstract

Thermal stability is essential for the survival and well-being of preterm neonates. This is achieved in neonatal incubators by raising the ambient temperature and humidity to sufficiently high levels. However, potentially pathogenic microorganisms also can thrive in such warm and humid environments. We therefore investigated whether the level of microbial contamination (i.e., the bacterial load) inside neonatal incubators can be predicted on the basis of their average temperature and relative humidity settings, paying special attention to local temperature differences. Swab samples were taken from the warmest and coldest spots found within Caleo incubators, and these were plated to determine the number of microbial CFU per location. In incubators with high average temperature (>34°C) and relative humidity (>60%) values, the level of microbial contamination was significantly higher at cold spots than at hot spots. This relates to the fact that the local equilibrium relative humidity at cold spots is sufficiently high to sustain microbial growth. The abundance of staphylococci, which are the main causative agents of late-onset sepsis in preterm neonates, was found to be elevated significantly in cold areas. These findings can be used to improve basic incubator hygiene.To increase the survival chances of premature infants, incubators have been developed which provide a thermoneutral environment. This environment must be defined in terms of temperature, humidity, convection, and surrounding radiant heat sources. The humidification of the incubators has helped in this respect, as the greatest heat loss by preterm neonates is due to evaporative transepidermal water loss. Increased relative humidity (RH) reduces the rate of evaporation and, as a consequence, not only reduces evaporative heat loss (4) but also helps to maintain the electrolyte and fluid balance of preterm neonates (7). Unfortunately, these conditions also increase the risk of microbial infection, because the moist and warm habitat created within an incubator is intrinsically ideal for microbial growth. A fine balance is sought between the thermal requirements of a newborn and the level of humidification and heating of the incubator. The highest levels of humidification and heating are used for the most immature infants with the lowest birth weights, as they have the most difficulty with maintaining their thermal stability (2, 8, 10). The humidification and heating levels are lowered slowly in the course of the first days and weeks after birth as the neonates' weight and the maturity of their skin barrier increase.The availability of water is one of the most important factors for microbial growth. Water availability on surface-to-air interfaces is determined by the local equilibrium relative humidity (RH e ). Molds require RH e values of at least 70%, and RH e values need to be even higher (80 to 95%) to allow for the growth of yeasts, Gram-positive bacteria, and Gram-negative bacteria; the latter group of bacteria require the highest RH e values (9). Th...

Potential NICU Environmental Influences on the Neonate's Microbiome

“…Several studies identified bacterial and fungal colonization of NICU surfaces, equipment, skin and caregiving supplies that are associated with nosocomial infections in the neonatal population. 16,29,30,34 Intensive care nurseries commonly engage in infection control bundles and routine cleaning of bedside and nursery equipment as a method to prevent nosocomial infections, and at least one study demonstrated a decrease in bacterial communities following routine cleaning practices. 16 However, how the routine cleaning might affect colonization of both commensal and pathogenic bacteria in infants is unclear.…”

“…In humidified Caleo® [[Dräger, Drägerwerk AG & Co. KGaA, Telford, PA.]] incubators with average temperatures ≥ 34°C and relative humidity levels ≥ 60%, microbial contamination with Staphylococcus was significantly higher at incubator cold spots than at hot spots. 34 The cold spots were found at the front, back sides and middle of the incubator where the humidified air did not reach as well. Hot spots were closer to the hot air vents.…”

“…Four studies examined several aspects of the NICU environment in an effort to better understand how they might impact the infant microbiome. 16,29,30,34 Specific measures utilized within these studies included sampling before and after cleaning with antibacterial wipes, 16 cold versus warm spot sampling in incubators, 34 predominant NICU organisms living within specific nurseries regardless of routine cleaning and hand washing, 29 and lack of hand washing and routine cleaning before and after implementing standard precautions. 30 Microbiome samples of environmental surfaces revealed complex and diverse environments and included species associated with nosocomial infections common in the neonatal population.…”

“…30 Microbiome samples of environmental surfaces revealed complex and diverse environments and included species associated with nosocomial infections common in the neonatal population. 16,29,34 Surfaces that came in direct contact with infants (continuous positive airway pressure machines, stethoscopes, ventilators, incubators, and radiant warmers) were colonized with Streptococcus, Staphylococcus, Neisseria, and Enterobacteriaceae 16,30 , while room environment surfaces (computer screens, a computer mouse, freezer handles, hand sanitizer bottles, door handles, telephones, heart rate monitor screens, and alarm buttons) were colonized with communities of Geobacillus, Halomonas, Shewanella, Acinetobacter, and Gemella. 16 Over time the surfaces with the greatest variation were those exposed to human skin.…”

Role of effective thermoregulation in premature neonates

“…De Goffau et al examined Caleo incubators for hot and cold spots in a group of infants housed in incubators kept at $34°C and $60% humidity versus a group of infants housed in incubators kept at ,34°C and ,60% humidity. 41 The researchers found prolific Staphylococcal bacteria in incubators with cold spots where the humidity level was above 60%. Cold spots were found in the incubators of the infants housed at lower temperatures and humidity; however, the bacteria were not present at a statistically significant higher level.…”