Journal of Hospital Infection (1989) 13, 27-31

Infection risks from electrically operated breast pumps

J. Ian Blenkharn

Department of Bacteriology, Royal Postgraduate Medical School, Hammer- smith Hospital, Ducane Road, London W12 ONN

Accepted for publication 3 June 1988

Summary: Using formula milk seeded with Staphylococcus epidermidis as indicator, bacteria were observed to pass beyond the collecting bottles of three electrically operated breast pumps. Bacteria were recovered from sites distal to the level of visible contamination, the incidence increasing with repeated use of the apparatus. Despite use of a sterile collecting bottle, retrograde contamination of freshly collected milk may occur from pre- viously contaminated components of the pumps. The results suggest that a terminal in-line air filter is essential to ensure aerosols containing potentially pathogenic bacteria do not contaminate the suction source or be emitted to the environment with the exhaust air. Where a single pump is used by more than one person adequate sterilization of all removable components is essential.

Keywords: Cross-infection; breast milk; breast pumps.

Introduction

Electrically* operated breast pumps are used in domiciliary and hospital practice to establish and maintain lactation. In hospitals, where a single unit is often shared between several patients, breast pumps are used for collecting milk for low birth weight or severely ill babies in neonatal intensive care units.

Episodes of infection with Pseudomonas aeruginosa (Thorn, Cole & Watrasiewicz, 1970). Klebsiella species (Donowitz et al., 1981) and Serratia marcescens (Moloney et al., 1987) have been recorded in which breast pumps were incriminated as vectors. Where milk banking is established, individual donations of ‘drip milk’ or expressed milk collected with a breast pump may be pooled before use, which may increase the probability of bacterial contamination (McEnery & Chattopadhyay, 1978; Williamson et al., 1978). Recommendations for safe use of electrically operated breast pumps (Thorn et al., 1970; Moloney et al., 1987) have been proposed. The routes by which neonatal infection may occur secondary to the use of this type of equipment have not been clearly defined; one potential route is the basis of this report.

J. I. Blenkharn

Methods

Breast pumps The Lactovac Junior and Lactovac Deluxe breast pumps (Aerosol Medical Limited, UK) and Egnell Lact E pump (Egnell Ameda Limited, UK) were examined. Lactovac Junior and Lactovac Deluxe breast pumps: These diaphragm pumps are similar in design and function (Figure 1). The operating vacuum range is O-250 mm Hg for the Lactovac Junior and 100-240 mm Hg for the Lactovac Deluxe. Each unit allows manually operated vacuum pulsing. The Lactovac Deluxe has an additional automatic vacuum pulse frequency of 30-120 cycles min-‘.

Both pumps are used with polycarbonate collecting bottles which can be used for storage and subsequent feeding of milk. Silicone tubing (50 cm) connects the polyethylene breast shield/collecting bottle assembly to the vacuum source, via an overflow protection device (‘Contamination Defence System’, Aerosol Medical Limited, UK) and a 0.3 p disposable micro glass fibre air filter which are positioned distal to the collecting bottle. All components are manufactured from materials suitable for heat or chemical sterilization. Lact E breast pump: This reciprocating piston-operated pump has a variable operating vacuum range of 120-230 mm Hg with a vacuum pulse frequency of 50 cycles min-‘. The reciprocating piston has a slotted rubber non-return valve for air venting to atmosphere and a variable vacuum release control. Plastic or glass collecting bottle/breast shield assemblies are available. These are connected to the pump unit with transparent PVC tubing 50 cm in length.

Figure 1. Lactovac breast pump. The Egnell Lact E pump, with piston-operated suction source mounted externally, is of similar basic configuration but has no overflow protection device.

Infection risks from breast pumps 29

Test method Pumps were used according to manufacturers’ recommendations. Prior to assembly, collecting bottle/breast shield assemblies were sterilized by autoclaving at 121°C for 15 min. PVC and heat sensitive plastic components (tubing, bottle caps etc) unsuitable for heat treatment were immersed, after thorough washing, in freshly prepared hypochlorite solution (1% available chlorine) for a minimum of 2 h, rinsed in sterile distilled water and drained thoroughly prior to use. 50 ml of sterile formula milk (Cow and Gate Premium Liquid Formula) was aspirated from a standard vented feeding bottle held tightly within the upright collecting bottle of each pump, with and without vacuum pulsing at pressures of approximately 100 and 200 mm Hg, over a period of 10 min. For each test condition, the procedure was repeated three times.

To evaluate distal contamination, milk seeded with lo4 cfuml-’ of a gentamicin resistant strain of Staphylococcus epidermidis (MIC 4.0 mg 1-l) was aspirated as above. Following aspiration, equipment was disassembled and removable components, including breast shield and connecting tube were examined for S. epidermidis using cotton tipped swabs moistened with Mueller-Hinton broth (Oxoid Ltd, UK). After sampling, swabs were placed in 10ml volumes of Mueller-Hinton broth containing 2.0mgll’ gentamicin and incubated at 37°C for 5 days. Additionally, the vacuum connection tube, situated within the equipment casing and connecting the suction motor and the vacuum regulator gauge, was similarly examined. This test procedure was repeated 10 times for each pump.

The cumulative effect of repeated aspiration of milk was evaluated by repeating the aspiration of seeded milk for five cycles for each pump, sampling individual components after each cycle. Components were re-assembled prior to each subsequent aspiration cycle without decontamination or sterilization. With the Lact E pump, the internal tubing to the vacuum release control and internal surface of the rubber non-return valve were also sampled for the presence of the indicator bacteria.

To evaluate retrograde spread of bacteria, 50 ml milk inoculated with S. epidermidis was aspirated to sterile collecting bottles followed by 50 ml sterile formula milk. Connecting tubing and, where fitted, the overflow protection device and air filter were used unchanged. Collecting bottles were allowed to stand for 15 min prior to their removal from the breast pump to allow condensation of any aerosol, then sealed for incubation at 37°C for 5 days. This procedure was repeated 10 times for each pump. Semi-quantitative estimation of the degree of contamination of the proximal connecting tube was performed by rinsing the entire 50 cm length of tubing after each cycle with 10 ml sterile water. Washings were cultured by surface inoculation of 0.5 ml volumes onto gentamicin-blood aga; medium.

30 J. I. Blenkharn

Results

After aspiration of 50 ml milk, visible contamination of the connecting tubing 4-5 cm distal to the breast shield/bottle assembly was observed, with all pumps examined. No differences were noted when milk was aspirated with or without vacuum pulsing or at high or low vacuum levels.

With the Lactovac pumps, indicator bacteria were recovered from the 5 cm portion of the connecting tube proximal to the filter on 9 of 10 occasions. The distal portion of this tubing, > 40 cm from the collecting bottle, and the overflow protection device harboured indicator bacteria on four occasions. The proximal aperture of two of 10 air filters were similarly contaminated. Repeated aspiration of milk, over five cycles but without change of breast shield and tubing showed a cumulative increase in the extent of contamination through the suction system. However, on no occasion did the clean side of any filter, or the suction motor and vacuum regulator gauge, yield the indicator strain of S. epidermidis. No differences were observed between the two Lactovac models tested.

Similar results were obtained with the Lact E pump. On six of 10 occasions indicator bacteria were recovered from the proximal 5 cm section of connecting tube. Bacteria were recovered on five consecutive occasions from the non-return valve and on three consecutive occasions from the vacuum release control. These internal components, positioned distal to the connecting tube, are not intended for removal or sterilization during normal operation. Thus, recovery of bacteria after consecutive sampling may indicate contamination on only a single occasion.

Aspiration of sterile milk to sterile collecting bottles, but without change of connecting tubing between the breast shield/collecting bottle assembly and the suction source previously used with S. epidermidis-seeded milk, showed little evidence for retrograde spread of bacteria. From all of 10 occasions with each type of pump when sterile milk was aspirated in this way, visible contamination of tubing immediately distal to the breast shield/collecting bottle assembly was observed. However, on only three of 10 occasions with the Lactovac pumps and two of 10 occasions with the Lact E pump were indicator bacteria recovered from milk within the previously sterilized collecting bottle. Washings from the entire length of the connecting tubes contained approximately lo* cfu ml-’ of the indicator bacterium.

Discussion

Breast milk collected using electrically operated pumps may be associated with neonatal infection, and episodes of cross-infection may occur particularly where apparatus is used by two or more nursing mothers (Thorn et al., 1970; Donowitz et al., 198 1; Moloney et al., 1987). The hazard is increased if milk collected in this way is given to premature and other high

Infection risks from breast pumps 31

risk neonates and the problem compounded by multiplication of contaminating bacteria during storage of milk.

Neonatal infection may be secondary to ingestion of milk contaminated during collection or by airborne dissemination of aerosols emitted from contaminated equipment. Aerosols are generated when fluid enters the collecting bottle under force and may pass through the apparatus with the exhaust air. Although contamination was observed to occur only within the proximal 4-5 cm of the connecting tube between suction source and collecting bottle, indicator bacteria were recovered from more distant sites. The incidence of distal contamination increased with repeated use of equipment. It is thus highly desirable that whenever possible all removable components are replaced or sterilized after each period of use and on every occasion prior to use by a second user.

To halt passage of aerosols, an effective 0.3 p air filter is essential (Blenkharn, 1986). Premature reduction of effective filter life is prevented by incorporation of an effective overflow protection device able to prevent passage of fluid and froth (Blenkharn, 1988). Filters must be regularly replaced although the optimum interval for change may be difficult to ascertain (Blenkharn, 1987).

Retrograde spread of bacteria, which may contaminate freshly aspirated milk, is of particular concern where breast pumps are shared by two or more users. This is an additional indication for regular heat or chemical sterilization, or single-use, of all removable components. Particular care must be taken during assembly of components to avoid contamination.

References

Blenkharn, J. I. (1986). Clinical Suction Apparatus: A Guide to Safe Use. Martin Group, Colchester.

Blenkharn, J. I. (1987). A new safety system for air filtration in clinical suction apparatus. Journal of Hospital Infection 10, 236-242.

Blenkharn, J. I. (1988). Safety devices to prevent airborne infection from clinical suction apparatus. Journal of Hospital Infection, 12, 109-l 15.

Donowitz, L. G., Marsik, F. J., Fisher, K. A. & Wenzel, R. P. (1981). Contaminated breast milk: a source of Klebsiella bacteraemia in a newborn intensive care unit. Reviews of Infectious Diseases 3, 716-720.

McEnery, G. Sz Chattopadhyay, B. (1978). Human milk bank in a District General Hospital. British Medical Journal 2, 794-796.

Moloney, A. C., Quoraishi, A. H., Parry, P. & Hall, V. (1987). A bacteriological examination of breast pumps. Journal of Hospital Infection 9, 169-l 74.

Thorn, A. R., Cole, A. P. & Watrasiewicz, K. (1970). Pseudomonas aeruginosa infection in a neonatal nursery possibly transmitted by a breast-milk pump. Lancet i, 560-561.

Williamson, S., Hewitt, J. H., Finucane, E. & Gamsu, H. R. (1978). Organisation of bank of raw and pasteurised milk for neonatal intensive care. British MedicalJournal 1,393-396.