Are laptop ventilation-blowers a potential source of nosocomial infections for patients?

Inadequately performed hand hygiene and non-disinfected surfaces are two reasons why the keys and mouse-buttons of laptops could be sources of microbial contamination resulting consequently in indirect transmission of potential pathogens and nosocomial infections. Until now the question has not been addressed whether the ventilation-blowers in laptops are actually responsible for the spreading of nosocomial pathogens. Therefore, an investigational experimental model was developed which was capable of differentiating between the microorganisms originating from the external surfaces of the laptop, and from those being blown out via the ventilation-blower duct. Culture samples were taken at the site of the external exhaust vent and temperature controls were collected through the use of a thermo-camera at the site of the blower exhaust vent as well as from surfaces which were directly exposed to the cooling ventilation air projected by the laptop. Control of 20 laptops yielded no evidence of microbial emission originating from the internal compartment following switching-on of the ventilation blower. Cultures obtained at the site of the blower exhaust vent also showed no evidence of nosocomial potential. High internal temperatures on the inner surfaces of the laptops (up to 73°C) as well as those documented at the site of the blower exhaust vent (up to 56°C) might be responsible for these findings.

Introduction

Based on the fact that computers are commonly used in hospital patient wards and operation theatres, it would be not surprising if they could be contaminated with nosocomial pathogens. Cultures taken from the surface of computers keyboards yielded microorganisms such as coagulase-negative staphylococcus (CNS) (from 100% of all keyboards), diphtheroids (80%), micrococcus spp. (72%), bacillus spp. (64%), Methicillin-resistant Staphylococcus aureus (MRSA; 4%), Methicillin-sensitive Staphylococcus aureus (MSSA; 4%), Vancomycin-sensitive enterococcus spp. (12%) and Gram-negative non-fermenting rods (36%) [1]. These studies found all of the tested disinfection solutions were to be effective and compatible for use in disinfecting keyboards. It could be further demonstrated that contamination of the keyboards used by numerous persons was far higher than that seen in keyboards used by only one person [2]. As a consequence to this unavoidable situation, Anderson et al. [2] also recommended routine cleaning and disinfection of the work station, especially in situations where keyboard usage involves numerous persons. On an intensive care unit it was discovered that the keyboard keys and mouse input devices of the ward station computers were contaminated up to 5.9% and 6.3%, respectively. Interestingly, the telephone handles as well as intercoms were not contaminated due to the fact that they were regularly disinfected [3]. Analogously, keyboard keys used by anesthesiologists in the operating room were also shown to be contaminated (most often with CNS and bacillus spp., but also with MRSA). Consequent to these findings, a recommendation was made for routine hand disinfection along with daily wipe-disinfection of the computer contact surface [4]. The general consensus from all of the studies examining computer keyboard and mouse devices is unanimous: the decisive preventative measure for the elimination of these infection sources is improved hand hygiene and routine disinfection/cleaning of the PC contact/touch surfaces [5], [6], [7], [8], [9], [10], [11], [12], [13].

Based upon the fact that most laptops are fitted with a cooling ventilation blower, it was decided to investigate whether the external air inlets into the vent and eventually blown back into the room actually culminates into contamination, thereby spreading potential pathogens into the surrounding area.

Materials and methods

In order to avoid a mixture of the emission from the laptop together with the surrounding contaminated environmental air, it had to be ascertained that the air exhausted from the laptop would be captured into a microbial air sampler, whereby a secure separation between contaminated room-air and laptop emission could be maintained. The laptops chosen for the study were examined within a laminar air flow safety workbench (Microflow, Nunc GmbH, Wiesbaden-Biebrich). For the purpose of this study a box which could be disinfected as well as completely sealed was constructed and placed into the security workbench (Figure 1 (Fig. 1)). The suction vent of the microbial air sampler (Air Deal 3 P, Biomerieux Deutschland GmbH,Nürtigen) was precisely positioned onto the opening punched out from the bottom of the box. The microbial air sampler has an aspiration capacity of 100 l/min. The top cover of the box could be open in order to place the laptop within (Figure 2 (Fig. 2)).

Figure 1

The box placed within the security workbench for the investigation of microbial emissions exhausted from laptops situated within the box

Figure 2

The metal box (which could be disinfected) and its perforated Plexiglas cover which facilitated circulation of the surrounding laminar air flow. The opening on the bottom of the box was the location where the microbial air sampler was securely joined.

Further course of the experiment involved the following steps:

Disinfection of all internal and external surfaces of the box using an alcohol-based surface disinfectant (Terralin liquid; Schülke and Mayr GmbH, Norderstedt) possessing microbiocidal and virocidal efficacy (declared max. effect time against non-sheathed viruses 2 min) for a minimal duration of 5 min

Simultaneous disinfection of the internal surfaces of the workbench with the same liquid solution also for 5 min with the safety workbench switched-on

Disinfection of the surface of the microbial air sampler with the same liquid solution for 5 min

Surgical, alcohol-based hand disinfection and disinfection of the lower arms according to the declared time of effect for duration of 1.5 min (AHD 2000, Lysoform, Dr. Hans Rosemann GmbH, Berlin), sterile OP gloves were subsequently put on

Placement of the disinfected box into safety workbench, thereafter the box was not moved

Switching-off of the safety workbench for the duration of time it took to carefully place the laptops into the box without causing any air-movement or disturbances

Switching-on of the safety workbench for a period of 20 sec

Disinfection of the gloved hands

Placement of the blood agar culture plate into the microbial air sampler, unscrewing the collection head which for the first measurement of the day was initially sterile. For each new subsequent measurement the collection head was disinfected for a duration period of 5 min with a bottled disinfection solution.

Careful attachment of the microbial air sampler to the opening at the bottom of the box with special attention not to allow any space between the connection (Figure 3 (Fig. 3))

Figure 3

Position of the microbial air sampler at the opening on the bottom of the box containing the laptop

Switching-on the microbial air sampler for a time period of 5 min in order to determine the “blank values”; that is the number of airborne bacteria released into the laminar air flow from the external body of the non-activated laptop

Removal of the agar plate from the microbial air sampler, disinfection of the collection head and placement of a new agar plate

Switching-on the laptop and program start; as soon as the ventilation fan is activated the microbial air sampler is immediately switched-on once again for a period of 5 min in order to register the air released by the ventilation blower

Removal of the laptop out of the box.

In parallel, a smear was taken using cotton swabs at the site of the laptop exhaust vent where the cooled air is blown out. The smear was then directly wiped onto Columbia-blood agar (heipha Dr. Müller GmbH, Eppelheim), subsequently placed into a Casein-Sojapepton-solution and vortexed. After 24 hr incubation of the CSL, 50 µl fractionated were spread onto Columbia blood agar. The blood agar plates were each incubated for 48 hr at 37±1°C.

The cultivated colonies derived from the collected air as well as those from the smear were biochemically differentiated in the same manner as those from enrichment cultures.

For this study only laptops with ventilation blowers were investigated. The devices originated from a total of 7 different manufacturers and were drafted for use from various hospital stations without prior notice or disinfection (Table 1 (Tab. 1)).

Table 1

Analyzed laptops

Temperature pictures were performed at the blower exhaust vent and within the interior of the laptop using a thermo camera VarioCAM high resolution (Infra Tec GmbH Dresden). For this the housing of the laptops were opened. In order to achieve a defined CPU-burden and the associated warmth development the software “Stress my PC” was installed and opened for use. Room temperature was 20°C at a distance of 0.5 m from the laptop.

Results

The pre-values derived from the air circulated around the casing of the laptop stood at 40.1±17.9 colony forming units per m3 (cfu/m3) (Table 2 (Tab. 2)). This represents an increased factor of 1.2. This difference was not considered significant. This was also found to be the case with molds whereby the factor was increased by only 1.2 (5.7±9.46 vs. 7.1±14.90).

Table 2

Release of microorganisms from laptops during a time span of 5 min air collection with or without the running ventilation blower

With the exception of the aerobic sporulation, there was no differentiation observed between the “blank values” and the running blowers in terms of species distribution. In the case of the apathogenic sporulators, the figures were doubled from 4.8±6.1 cfu/m3 to 11.1±13.2 cfu/m3 whereby, however, this difference was not considered significant (Wilcoxon signed rank-test , p=0.211).

The spectrum of the freely released microorganisms encompassed mostly members of the localized flora of the skin (coagulase-negative staphylococcus and micrococcus luteus), lacking pathogenic potential and therefore only capable of contaminating the body surface. From 2 laptops were 4 cfu of Methicillin sensitive staphylococcus aureus released but each time only for the blank values (laptops 2 & 12). 1 laptop released 2 cfu of β-hemolyzing streptococcus but in this case only after the blower was switched-on.

A correlation between origin of the laptop, the manufacturer, the amount of freely-released germs as well as germ spectrum could not be developed.

Swab culture samples taken from the blower exit vents which were directly smeared demonstrated negative growth in 16 of the cases. The remaining 4 showed only members of the localized flora of the skin and/or aerobic spores. Even following applied enrichment, 6 of the smears remained negative and the germ spectrum did not alter (Table 3 (Tab. 3)). The results were found to be so uniform that it was decided not to match the results to the specific laptop manufacturers.

Table 3

Microbial contaminations at the site of the blower exit vent

At the site of the blower exit vent of a laptop model TravelMate 3000 following 10 min of running the software at maximum, measured temperature 56.4°C (Figure 4 (Fig. 4)).

Figure 4

Thermographic picture at the site of the blower vent

Suctioned cool air flowing over the internal surface of the laptop achieved a measured temperature of 73.2°C (Figure 5 (Fig. 5)).

Figure 5

Thermographic picture of the internal space (CPU-region)

Discussion

The results of this study allow the assumption that the activated blowers within the investigated laptops did not result in an additional release of nosocomial pathogens into the surrounding environment. The exit vent of the blower was also not contaminated with nosocomial germs.

Due to the high temperatures in the inner parts of the laptop (up to 73°C), a biofilm could not be created within the blower space or surrounding surfaces from which the risk of disease activators could be emitted. Even at the site of the blower vent there was no evidence for aerobic spores or mold. This could be explained by the high exhaust temperature of 56°C. The fact that spores were released with or without the activated blower leads to the assumption that they originated from the external surface of the laptop and perhaps from the air shaft of the blower. That spores and molds possess a high persistence against dry heat than vegetative bacteria; it is possible that they could survive a short term within the airspace of the blower. This is, however, unlikely for nosocomial vegetative bacteria due to an intolerance of general temperatures ≥60°C. Before the point is reached where the processor has become heated-up and the blower is activated, the surrounding room air is sucked into the device. The air becomes immediately warm and dry, whereby bacteria have no possibility of clinging to the inner surface of the blower, reproducing and eventually building a biofilm. The explanation for this is that most disease activators are mesophilic; meaning that they proliferate preferably at temperatures between 15–45°C [14] and for the construction of biofilm require water in order to develop a completely hydrated EPS-matrix [15]. Interpretation of the findings is thereby supported in that direct smears obtained from the airflow ventilated inner surface of the laptop were without exception negative. Only the aerobic spores could be cultivated post enrichment.

Once the remaining warm air within the airspace of the blower is cooled after the laptop has been switched-off, it is possible through volume traction that contaminated external air finds its way into the blower compartment. That room air within ward stations is minimally burdened in a microbial sense (e.g. 200–400 cfu/m3 in a patient room and hall of an ICU ward [13], it can be calculated that after a room air backflow of approximately 2 cm3, the number of germs which had entered clearly stood at ≤1 cfu. Even though the cooling blower was turned-off the conditions for biofilm development were not present.