- Email: [email protected]
The milk kitchen, Sheffield Children's Hospital, before and after a review
Journal
of Hospital
Infection
(1989)
13, 179-185
INFECTION
The milk
kitchen, before
I. A. Burnett, Department
CONTROL
Sheffield and after B. L. Wardley
IN PRACTICE
Children’s a review
and J. T. Magee
of Microbiology
and Department of Dietetics, Hospital, Shefield SlO 2TH
Accepted for publication
Hospital,
26 August
The Children’s
1988
Summary: The milk kitchen at Sheffield Children’s Hospital has recently been modernized to update equipment and practices. Microbiological assessments before, during and after this upgrading are described. Limits for viable counts in pasteurized feeds are suggested and the practices adopted to minimize the contamination of feeds are described. Keywords:
Milk
feeds,
SCBU
kitchen.
Introduction Microbial contamination of food and drink presents a hazard to all, but particularly the young, the old, and the sick. In hospitals, where the ill and frail are concentrated, food poisoning acquires an enhanced importance. In immunocompromised patients the dangers of enteric colonization with abnormal flora and consequent risk of systemic infection must be considered. (Selden et al., 1971). M’ icrobial contamination of tube feeds and sip feeds is well documented (Anderton, 1983), and an episode of contamination of infant feeds has been reported (Ayliffe, Collins & Pettit, 1970). We report the results of a review of our practices in the milk kitchen of a 160-bedded unit which serves the Sheffield District and acts as a reference centre for the Trent Region. Before the review The milk kitchen comprised two adjacent lower ground floor rooms plus a small office/store room with a separate toilet and handwash basin. The smaller of the two main rooms was a washing up area with a single door to a hospital corridor. The larger room was used for feed preparation, and had doors leading to the corridor, and office/store room. The washing-up room contained a domestic dish washer, double drainer twin sink unit, two work benches, wall cupboards and one door of a double 0195-6701/89/020179+07
0 1989 The Hospital
$03.00/O
179
Infection
Society
180
I. A. Burnett
et al.
ended autoclave. The feed preparation room housed a domestic sink unit, a Stills-hot water unit, an electric geyser attached to the mains by a detachable rubber hose, a purpose built pasteurizer and the other door of the double ended autoclave. It also contained work benches and wall cupboards, a freezer and three double ended wall refrigerators which opened onto the corridor. This room was separated into a weighing and mixing area and a pasteurizer/refrigerator area by an island bench. Ventilation was provided by two air conditioning units installed in the windows, one situated over the pasteurizer, the other over the weighing bench. Three auxiliary nurses and a domestic were employed whose hours ranged from 20-37 per week. Feeds, prepared for the Children’s Hospital and Jessop’s Hospital for Women, comprised mainly special dietetic formulas such as Pregestimil (Mead Johnson), Nutramigen (Mead Johnson) and Cornminuted Chicken Meat (Cow and Gate), but included standard infant formula feeds such as S.M.A. Gold Cap (Wyeth), Premium (Cow and Gate) and milk formulations for older children such as Build-Up (Carnation). Total production was 60-80 bottled feeds/day. The autoclave was used to sterilise bottles, caps, mixer bowls and feed preparation utensils. Prepared formulations were bottled in single-feed, single-patient portions. All infant feeds were then pasteurized; non-infant feeds were not. Prepared feeds were stored in ward or milk kitchen refrigerators for not more than 24 h. Feeds were delivered to the wards each day by kitchen staff who removed the time-expired feeds. No routine bacteriological monitoring was performed. The review In January, 1986 the dietetic department was asked to take over management of the milk kitchen and a review was conducted jointly by the chief dietitian and the microbiology department. In the preparation and filling room, two large dirty inaccessible pipes were suspended below the ceiling; these crossed above the autoclave door, sink and weighing and mixing area. Dirt and dust had been seen to fall from these and from the air conditioning units which were inaccessible and found to be broken. Gaps between the wooden edging and surface of the benches allowed dirt to accumulate. The drive heads of the electric mixers could not be dismantled for cleaning and the freezer was not in working order. The autoclave had no chart temperature recorder, although preparations were in hand to institute daily monitoring with Browne’s tubes, to maintain written records of the results and to indicate the sterilization status of bottles with autoclave tape. The pasteurizer, which required increasingly frequent repairs, also lacked a temperature chart recorder. The refrigerators were at lO”C, an unacceptably high temperature. Recommendations were made by the Principal Microbiologist based upon these findings. Some were instituted immediately, including charting of refrigerator temperatures which were reset to 4”C, posting a notice
Milk
kitchen
review
181
warning staff to boil the water in the geyser/boiler unit for > 2 min before use in feeds, and a scheme for microbiological testing of any feeds returned for reasons other than being out of date. Further recommendations were that the autoclave and pasteurizer should either be replaced or fitted with adequate temperature recording apparatus as soon as possible, and that a working freezer was essential for storage of prepared feeds for > 24 h. Use of chemical disinfection for bottle and kitchen equipment was rejected; experience suggests that autoclaving is preferable (Bolton, 1966; Ayliffe, Collins & Pettit, 1970). The importance of pasteurization has been stressed on many occasions (Gamsu, Cawdery & Taylor, 1969; Howie, 1985, Sharp, Paterson & Barrett, 198.5) and requires no further comment. Bacteriological sampling of prepared feeds was instituted immediately. Formulations produced on a daily basis were sampled 2-3 times/week; those prepared less frequently were sampled whenever these were required for patients. If > 1 pasteurization cycle occurred within a day, a sample was taken from each load. Ingredients, and pre- and post-pasteurization samples of the same feed were taken less frequently. After 4 months all formulations had been sampled. Samples comprised a single bottle of feed, prepared and pasteurized in the normal way. Dry powdered ingredients were sampled by suspending 1 g in 10 ml of sterile saline. A simple plating procedure was chosen to minimise costs: three 0.5 ml samples of milk were spread on two blood agar plates (Columbia agar base, Oxoid, with 5% horse blood, Gibco), one for aerobic incubation and one for anaerobic incubation in a CO, enriched atmosphere, and a MacConkey plate (MacConkey Agar LabM 2) for aerobic incubation without added CO,. These were incubated at 37°C for 48 h. Aerobic spore-forming bacilli (ASBs) predominated in the “normal flora” of the dry powdered ingredients, and counts of these were affected little by pasteurization, presumably because they were present as dormant, heat resistant spores. Pre-pasteurization counts of feeds were low; ASBs predominated, with occasional coagulase-negative staphylococci. The pasteurization process eliminated all bacteria other than ASBs, counts of which were low (rarely > 100 ml-‘); no anaerobic bacteria were isolated. On one occasion an unpasteurized product yielded > 10000 ml-’ Pseudomonas aeruginosa. Environmental swabs were taken, the mixing process was observed on two occasions, and the feed sampled. On the first occasion no abnormalities were noted and only ASBs were isolated (< 10 ml-‘). On the second occasion a plunger-action hand-held rotary whisk was used to mix the feed. This had a hollow handle enclosing a twisted shank; when the whisk was immersed during washing, water entered the handle and was retained, protected from evaporation loss during storage, providing a growth medium and source of bacterial contamination. In mixing, downward pressure pushed the shank into the handle and rotated the mixer blades. Wash water retained in the handle, which now contained large numbers of P. aeruginosa, was concurrently sprayed into the feed. Swabs from the feed, whisk and sites on the sink yielded five isolates of P.
182
I. A. Burnett
et al.
aeruginosa, all of which were found to be pyocine type 19 (Gillies & Govan, 1966). The whisk was immediately withdrawn from use, and the problem resolved. This was the only incident of major contamination; despite ageing and unsuitable equipment, the staff were diligent and produced feeds with minimal contamination. After the review Renovation was carried out in accordance with the recommendations. A locking door was fitted, preventing unauthorized access to the feed preparation area, bench edging and surfaces were replaced, the pipe run was enclosed and the air conditioning units were replaced with extractor (Ventaxia) fans. The pasteurizer was replaced and the autoclave was removed; both had been scheduled for replacement, because the hospital piped steam facility was to be withdrawn. The CSSD at the nearby Royal Hallamshire Hospital now provides an autoclaving service. The pasteurizer was replaced with purpose built apparatus (Grant Instruments), comprising a thermostatically controlled heated water bath with temperature recorder, and a cooled water bath. The water for each bath is recirculated through external pipework and pumps. The cooled bath contains a refrigeration coil which becomes coated with ice during operation, maintaining the temperature at c. 0°C. The heated bath is maintained at a temperature which heats the bottled feed to 67.5”C for 4 min during the standard pasteurization cycle. The equipment was calibrated by and District Sterilizer Engineer. The internal the manufacturer temperature of a dummy feed bottle is now recorded via a thermocouple during each pasteurization cycle. Pasteurized feeds are immediately chilled to < 10°C within 2.5 min in the cooled water bath. This pasteurization cycle was used at the Great Ormond Street Hospitals for Sick Children and Chief Dietitian (Personal recommended by D. Francis, Group communication, 1984). New working procedures have been introduced. Persons entering the milk kitchen are provided with a clean white coat to wear. The work surfaces are cleaned with hypochlorite solution before feed preparation. The staff wear clean caps (Department of Health and Social Security, 1986) and disposable plastic aprons whilst mixing feeds, which are poured directly into sterile feeding bottles. All feeds are now pasteurized. For mixing, hand whisks, a Braun electric whisk and a Kenwood food processor have been introduced. The blades of the electric mixers are removed and washed in the bottle wash area along with the mixing bowls and whisks before being packed and sent for sterilization. Feeding bottles and non-disposable teats are treated in the same way, the teats being packaged individually for autoclaving. Protocols were written for the preparation of each type of formulation. The following general principles were emphasized. (1) Feeds should be prepared from ingredients stored in suitable conditions, that are within date and show no evidence of spoilage.
Milk
kitchen
review
183
(2) Water used should be freshly taken drinking water; if water is taken from a geyser tank this should be boiled for > 2 min and used promptly. (3) Feeds should be mixed in sterile containers, with sterile equipment under hygienic conditions, and distributed into sterile, single feed containers, labelled and dated appropriately. (4) These containers should be pasteurized within 1 h of mixing. (5) The temperature recording of each pasteurization cycle should be inspected, and all abnormalities reported immediately. (6) The feeds should be cooled rapidly, inspected for cracks, and distributed to refrigerators or freezers as quickly as possible. No feeds should remain at room temperature for more than 1 h. (7) The milk kitchen staff are responsible for removal of outdated feeds from refrigerators (24 h shelf life) and freezers (12 week shelf life). The control of infection nurse checks the temperature of all ward refrigerators on a weekly, or, if problems arise, daily basis. Feeds for weekends are made on Friday, pasteurized, cooled and frozen immediately in the domestic freezers; small stocks of some feeds are maintained there, and in a freezer on the neonatal surgical unit. Production remains at 60-100 feeds/day, mostly for Sheffield Children’s Hospital, In addition, the kitchen supplies although other units are supplied. commercial ready-to-use infant formulas such as Premium (Cow and Gate) and SMA Goldcap (Wyeth), sterile teats, feeding bottles and naso-gastric feeding equipment. Disposable teats are used predominately, but a variety of autoclaved re-usable teats are available for the requirements of individual patients. The four members of the kitchen staff work on a rota covering 8am4pm, Monday to Friday, and Sam-lpm Saturday and Sunday. Hours total 100 per week consisting of four 2.5 h sessions, an arrangement which enables holidays and weekends to be covered more easily. All staff are of assistant cook grade and every duty may be carried out by each member of staff without demarcation. Staff are directly responsible to the chief dietitian who manages the unit and organizes staff training which includes sessions by the microbiologist. During part of the renovation, feeds had to be supplied from another milk kitchen c. 30 miles away. The quality of feeds transported in cold boxes was found to be adequate in several trial runs, and this arrangement proved satisfactory in practice. Th e value of this established procedure was demonstrated later, when an unexpected breakdown prevented production in Sheffield, and this arrangement was re-instated rapidly, with a minimum of problems. The current policy for bacteriological monitoring is to examine at least three post-pasteurization specimens per day, with a specimen from each pasteurization run. Because no anaerobes were isolated during the review, 0.5 ml samples are plated on one aerobic blood agar and one MacConkey agar and incubated at 30°C for 48 h; this lower temperature gave slightly increased counts. Recovery of enterobacteria, staphylococci or other heat
184
I. A. Burnett
et al.
sensitive bacteria is deemed a failure. An arbitrary limit of < 500 ASB ml-’ was chosen for three reasons-(l) higher counts might obscure other organisms; (2) > 90% of feeds had 5 100 ASB ml-’ and > 99% had counts of < 500 ASB ml-‘, making the latter a suitable cut off; (3) counts > 500 ASB ml-’ would be exceptional, possibly indicating growth of these bacilli. In the light of experience, counts >200ml-’ are now considered exceptional, and a limit of ~200 ASB ml-’ is being considered. With human breast milk the predominant flora comprises heat sensitive skin commensal organisms and lower post-pasteurization limits can be supported, e.g., < 5 ml -’ (Baum, Fisher & Smith, 1980). The water in the pasteurizer water baths is monitored bacteriologically, as a crack in a bottle could result in water being drawn into the feed along with contaminating bacteria. Samples are taken weekly and 0.5 ml plated as for feed samples. Counts for the heated bath remained< 1 ml-‘, but within 8 weeks a steadily rising level of P. aeruginosa was found in the cooling bath, despite draining, cleaning and refilling at weekly intervals. There was no evidence of feed contamination. Routine disinfection of the water bath with Milton solution failed to eliminate the organism; recirculation of Milton through the external circulation pump was more successful but these intermittent measures failed to resolve the problem. A slow release acid) was added, maintaining chlorinating agent (trichlorcyanuric concentrations of 1-3 ppm available chlorine. This reduced the count of bacteria to < 2 ml-‘, a level consistently maintained for > 1 year. The baths are now drained, cleaned and refilled at monthly intervals. Available chlorine is estimated weekly by the works department, and chlorinating agent added to the cooling bath as required. Discussion
Recommendations for the provision and equipping of a milk kitchen have been made (Bolton, 1966; Maternity Services Advisory Commitee, 1985; Hicks & MacGregor, 1968) but the needs of an individual unit will vary in accordance with the size and type of hospital. A mutual aid agreement with a neighbouring milk kitchen, to allow continued supply of feeds in the event of a breakdown, seems to us essential; these arrangements should be tested in practice. Our intention was to ensure that any single failure in procedures or equipment should be covered by good practice at every other stage, e.g., failure of pasteurization should not be disastrous, provided that feeds have acquired minimal contamination during preparation, and growth is not allowed to occur subsequently. In this, we depend on the manufacturer’s quality control of dry powder ingredients, as resources are too limited for comprehensive sampling. With this proviso, good management should, hopefully, prevent disastrous simultaneous multiple failures. However, the incident of
Milk
kitchen
review
185
contamination from the whisk clearly illustrates that problems may arise from unlikely sources: vigilance, good communications and bacteriological monitoring are required to prevent and solve such problems. Sampling provides the microbiologist with an opportunity for regular visits, to build up a good liaison with the milk kitchen staff, and to observe the production of feeds; these aspects were as important in establishing good practices as the monitoring process itself.
References Anderton, A. (1983). Microbiological aspects of the preparation and administration of nasogastric and naso-enteric feeds in hospital-A review. Human Nutrition: Applied Nutrition 37A, 426440. Ayliffe, G. A. J., Collins, B. J. & Pettit, F. (1970). Contamination of infant feeds in a Milton milk kitchen. Lancet i, 599-560. Baum, J. D., Fisher, C. & Smith, A. (1980). A Guide to Human Milk Banking. Vickers Medical, Basingstoke, U.K. Bolton, J. (1966). The infant formula room. Hospital Journal and Social Services Review February 4, 1966, 211-216. Department of Health and Social Security (1986). Health Service Catering Hygiene. HMSO, London. Gamsu, H. R., Cawdery, H. M. & Taylor C. G. (1969). Hospital milk kitchen. Lancet i, 1094-1050. Gillies, R. R. & Govan, J. R. W. (1966). Typing of Pseudomonas pyocyanea by pyocine production. Journal of Pathology and Bacteriology 91, 339-345. Hicks, M. & MacGregor, M. E. (1968). Modernising a milk kitchen. Nursing Mirror October 18, 1968, 31-33. Howie, J. (1985). The case for compulsory pasteurisation. British Medical Journal, 291, 422-423. Maternity Services Advisory Committee (MSAC) (1985). Maternity care in action part III. Care of the mother and baby. Third report of the Maternity Services Advisory Committee to the Secretaries of State for Social Services and for Wales. HMSO, London. Seldon, R., Lee, S., Wang, W. L. L., Bennett, J. V. & Eickhoff, T. C. (1971). Nosocomial klebsiella infections: intestinal colonization as a reservoir. Annals of Internal Medicine 74, 657-664. Sharpe, J. C. M., Paterson, G. M. & Barrett, N. J. (1985). Pasteurisation and the control of milkborne infection in Britain. British MedicalJournal 291, 463-464.
of Hospital
Infection
(1989)
13, 179-185
INFECTION
The milk
kitchen, before
I. A. Burnett, Department
CONTROL
Sheffield and after B. L. Wardley
IN PRACTICE
Children’s a review
and J. T. Magee
of Microbiology
and Department of Dietetics, Hospital, Shefield SlO 2TH
Accepted for publication
Hospital,
26 August
The Children’s
1988
Summary: The milk kitchen at Sheffield Children’s Hospital has recently been modernized to update equipment and practices. Microbiological assessments before, during and after this upgrading are described. Limits for viable counts in pasteurized feeds are suggested and the practices adopted to minimize the contamination of feeds are described. Keywords:
Milk
feeds,
SCBU
kitchen.
Introduction Microbial contamination of food and drink presents a hazard to all, but particularly the young, the old, and the sick. In hospitals, where the ill and frail are concentrated, food poisoning acquires an enhanced importance. In immunocompromised patients the dangers of enteric colonization with abnormal flora and consequent risk of systemic infection must be considered. (Selden et al., 1971). M’ icrobial contamination of tube feeds and sip feeds is well documented (Anderton, 1983), and an episode of contamination of infant feeds has been reported (Ayliffe, Collins & Pettit, 1970). We report the results of a review of our practices in the milk kitchen of a 160-bedded unit which serves the Sheffield District and acts as a reference centre for the Trent Region. Before the review The milk kitchen comprised two adjacent lower ground floor rooms plus a small office/store room with a separate toilet and handwash basin. The smaller of the two main rooms was a washing up area with a single door to a hospital corridor. The larger room was used for feed preparation, and had doors leading to the corridor, and office/store room. The washing-up room contained a domestic dish washer, double drainer twin sink unit, two work benches, wall cupboards and one door of a double 0195-6701/89/020179+07
0 1989 The Hospital
$03.00/O
179
Infection
Society
180
I. A. Burnett
et al.
ended autoclave. The feed preparation room housed a domestic sink unit, a Stills-hot water unit, an electric geyser attached to the mains by a detachable rubber hose, a purpose built pasteurizer and the other door of the double ended autoclave. It also contained work benches and wall cupboards, a freezer and three double ended wall refrigerators which opened onto the corridor. This room was separated into a weighing and mixing area and a pasteurizer/refrigerator area by an island bench. Ventilation was provided by two air conditioning units installed in the windows, one situated over the pasteurizer, the other over the weighing bench. Three auxiliary nurses and a domestic were employed whose hours ranged from 20-37 per week. Feeds, prepared for the Children’s Hospital and Jessop’s Hospital for Women, comprised mainly special dietetic formulas such as Pregestimil (Mead Johnson), Nutramigen (Mead Johnson) and Cornminuted Chicken Meat (Cow and Gate), but included standard infant formula feeds such as S.M.A. Gold Cap (Wyeth), Premium (Cow and Gate) and milk formulations for older children such as Build-Up (Carnation). Total production was 60-80 bottled feeds/day. The autoclave was used to sterilise bottles, caps, mixer bowls and feed preparation utensils. Prepared formulations were bottled in single-feed, single-patient portions. All infant feeds were then pasteurized; non-infant feeds were not. Prepared feeds were stored in ward or milk kitchen refrigerators for not more than 24 h. Feeds were delivered to the wards each day by kitchen staff who removed the time-expired feeds. No routine bacteriological monitoring was performed. The review In January, 1986 the dietetic department was asked to take over management of the milk kitchen and a review was conducted jointly by the chief dietitian and the microbiology department. In the preparation and filling room, two large dirty inaccessible pipes were suspended below the ceiling; these crossed above the autoclave door, sink and weighing and mixing area. Dirt and dust had been seen to fall from these and from the air conditioning units which were inaccessible and found to be broken. Gaps between the wooden edging and surface of the benches allowed dirt to accumulate. The drive heads of the electric mixers could not be dismantled for cleaning and the freezer was not in working order. The autoclave had no chart temperature recorder, although preparations were in hand to institute daily monitoring with Browne’s tubes, to maintain written records of the results and to indicate the sterilization status of bottles with autoclave tape. The pasteurizer, which required increasingly frequent repairs, also lacked a temperature chart recorder. The refrigerators were at lO”C, an unacceptably high temperature. Recommendations were made by the Principal Microbiologist based upon these findings. Some were instituted immediately, including charting of refrigerator temperatures which were reset to 4”C, posting a notice
Milk
kitchen
review
181
warning staff to boil the water in the geyser/boiler unit for > 2 min before use in feeds, and a scheme for microbiological testing of any feeds returned for reasons other than being out of date. Further recommendations were that the autoclave and pasteurizer should either be replaced or fitted with adequate temperature recording apparatus as soon as possible, and that a working freezer was essential for storage of prepared feeds for > 24 h. Use of chemical disinfection for bottle and kitchen equipment was rejected; experience suggests that autoclaving is preferable (Bolton, 1966; Ayliffe, Collins & Pettit, 1970). The importance of pasteurization has been stressed on many occasions (Gamsu, Cawdery & Taylor, 1969; Howie, 1985, Sharp, Paterson & Barrett, 198.5) and requires no further comment. Bacteriological sampling of prepared feeds was instituted immediately. Formulations produced on a daily basis were sampled 2-3 times/week; those prepared less frequently were sampled whenever these were required for patients. If > 1 pasteurization cycle occurred within a day, a sample was taken from each load. Ingredients, and pre- and post-pasteurization samples of the same feed were taken less frequently. After 4 months all formulations had been sampled. Samples comprised a single bottle of feed, prepared and pasteurized in the normal way. Dry powdered ingredients were sampled by suspending 1 g in 10 ml of sterile saline. A simple plating procedure was chosen to minimise costs: three 0.5 ml samples of milk were spread on two blood agar plates (Columbia agar base, Oxoid, with 5% horse blood, Gibco), one for aerobic incubation and one for anaerobic incubation in a CO, enriched atmosphere, and a MacConkey plate (MacConkey Agar LabM 2) for aerobic incubation without added CO,. These were incubated at 37°C for 48 h. Aerobic spore-forming bacilli (ASBs) predominated in the “normal flora” of the dry powdered ingredients, and counts of these were affected little by pasteurization, presumably because they were present as dormant, heat resistant spores. Pre-pasteurization counts of feeds were low; ASBs predominated, with occasional coagulase-negative staphylococci. The pasteurization process eliminated all bacteria other than ASBs, counts of which were low (rarely > 100 ml-‘); no anaerobic bacteria were isolated. On one occasion an unpasteurized product yielded > 10000 ml-’ Pseudomonas aeruginosa. Environmental swabs were taken, the mixing process was observed on two occasions, and the feed sampled. On the first occasion no abnormalities were noted and only ASBs were isolated (< 10 ml-‘). On the second occasion a plunger-action hand-held rotary whisk was used to mix the feed. This had a hollow handle enclosing a twisted shank; when the whisk was immersed during washing, water entered the handle and was retained, protected from evaporation loss during storage, providing a growth medium and source of bacterial contamination. In mixing, downward pressure pushed the shank into the handle and rotated the mixer blades. Wash water retained in the handle, which now contained large numbers of P. aeruginosa, was concurrently sprayed into the feed. Swabs from the feed, whisk and sites on the sink yielded five isolates of P.
182
I. A. Burnett
et al.
aeruginosa, all of which were found to be pyocine type 19 (Gillies & Govan, 1966). The whisk was immediately withdrawn from use, and the problem resolved. This was the only incident of major contamination; despite ageing and unsuitable equipment, the staff were diligent and produced feeds with minimal contamination. After the review Renovation was carried out in accordance with the recommendations. A locking door was fitted, preventing unauthorized access to the feed preparation area, bench edging and surfaces were replaced, the pipe run was enclosed and the air conditioning units were replaced with extractor (Ventaxia) fans. The pasteurizer was replaced and the autoclave was removed; both had been scheduled for replacement, because the hospital piped steam facility was to be withdrawn. The CSSD at the nearby Royal Hallamshire Hospital now provides an autoclaving service. The pasteurizer was replaced with purpose built apparatus (Grant Instruments), comprising a thermostatically controlled heated water bath with temperature recorder, and a cooled water bath. The water for each bath is recirculated through external pipework and pumps. The cooled bath contains a refrigeration coil which becomes coated with ice during operation, maintaining the temperature at c. 0°C. The heated bath is maintained at a temperature which heats the bottled feed to 67.5”C for 4 min during the standard pasteurization cycle. The equipment was calibrated by and District Sterilizer Engineer. The internal the manufacturer temperature of a dummy feed bottle is now recorded via a thermocouple during each pasteurization cycle. Pasteurized feeds are immediately chilled to < 10°C within 2.5 min in the cooled water bath. This pasteurization cycle was used at the Great Ormond Street Hospitals for Sick Children and Chief Dietitian (Personal recommended by D. Francis, Group communication, 1984). New working procedures have been introduced. Persons entering the milk kitchen are provided with a clean white coat to wear. The work surfaces are cleaned with hypochlorite solution before feed preparation. The staff wear clean caps (Department of Health and Social Security, 1986) and disposable plastic aprons whilst mixing feeds, which are poured directly into sterile feeding bottles. All feeds are now pasteurized. For mixing, hand whisks, a Braun electric whisk and a Kenwood food processor have been introduced. The blades of the electric mixers are removed and washed in the bottle wash area along with the mixing bowls and whisks before being packed and sent for sterilization. Feeding bottles and non-disposable teats are treated in the same way, the teats being packaged individually for autoclaving. Protocols were written for the preparation of each type of formulation. The following general principles were emphasized. (1) Feeds should be prepared from ingredients stored in suitable conditions, that are within date and show no evidence of spoilage.
Milk
kitchen
review
183
(2) Water used should be freshly taken drinking water; if water is taken from a geyser tank this should be boiled for > 2 min and used promptly. (3) Feeds should be mixed in sterile containers, with sterile equipment under hygienic conditions, and distributed into sterile, single feed containers, labelled and dated appropriately. (4) These containers should be pasteurized within 1 h of mixing. (5) The temperature recording of each pasteurization cycle should be inspected, and all abnormalities reported immediately. (6) The feeds should be cooled rapidly, inspected for cracks, and distributed to refrigerators or freezers as quickly as possible. No feeds should remain at room temperature for more than 1 h. (7) The milk kitchen staff are responsible for removal of outdated feeds from refrigerators (24 h shelf life) and freezers (12 week shelf life). The control of infection nurse checks the temperature of all ward refrigerators on a weekly, or, if problems arise, daily basis. Feeds for weekends are made on Friday, pasteurized, cooled and frozen immediately in the domestic freezers; small stocks of some feeds are maintained there, and in a freezer on the neonatal surgical unit. Production remains at 60-100 feeds/day, mostly for Sheffield Children’s Hospital, In addition, the kitchen supplies although other units are supplied. commercial ready-to-use infant formulas such as Premium (Cow and Gate) and SMA Goldcap (Wyeth), sterile teats, feeding bottles and naso-gastric feeding equipment. Disposable teats are used predominately, but a variety of autoclaved re-usable teats are available for the requirements of individual patients. The four members of the kitchen staff work on a rota covering 8am4pm, Monday to Friday, and Sam-lpm Saturday and Sunday. Hours total 100 per week consisting of four 2.5 h sessions, an arrangement which enables holidays and weekends to be covered more easily. All staff are of assistant cook grade and every duty may be carried out by each member of staff without demarcation. Staff are directly responsible to the chief dietitian who manages the unit and organizes staff training which includes sessions by the microbiologist. During part of the renovation, feeds had to be supplied from another milk kitchen c. 30 miles away. The quality of feeds transported in cold boxes was found to be adequate in several trial runs, and this arrangement proved satisfactory in practice. Th e value of this established procedure was demonstrated later, when an unexpected breakdown prevented production in Sheffield, and this arrangement was re-instated rapidly, with a minimum of problems. The current policy for bacteriological monitoring is to examine at least three post-pasteurization specimens per day, with a specimen from each pasteurization run. Because no anaerobes were isolated during the review, 0.5 ml samples are plated on one aerobic blood agar and one MacConkey agar and incubated at 30°C for 48 h; this lower temperature gave slightly increased counts. Recovery of enterobacteria, staphylococci or other heat
184
I. A. Burnett
et al.
sensitive bacteria is deemed a failure. An arbitrary limit of < 500 ASB ml-’ was chosen for three reasons-(l) higher counts might obscure other organisms; (2) > 90% of feeds had 5 100 ASB ml-’ and > 99% had counts of < 500 ASB ml-‘, making the latter a suitable cut off; (3) counts > 500 ASB ml-’ would be exceptional, possibly indicating growth of these bacilli. In the light of experience, counts >200ml-’ are now considered exceptional, and a limit of ~200 ASB ml-’ is being considered. With human breast milk the predominant flora comprises heat sensitive skin commensal organisms and lower post-pasteurization limits can be supported, e.g., < 5 ml -’ (Baum, Fisher & Smith, 1980). The water in the pasteurizer water baths is monitored bacteriologically, as a crack in a bottle could result in water being drawn into the feed along with contaminating bacteria. Samples are taken weekly and 0.5 ml plated as for feed samples. Counts for the heated bath remained< 1 ml-‘, but within 8 weeks a steadily rising level of P. aeruginosa was found in the cooling bath, despite draining, cleaning and refilling at weekly intervals. There was no evidence of feed contamination. Routine disinfection of the water bath with Milton solution failed to eliminate the organism; recirculation of Milton through the external circulation pump was more successful but these intermittent measures failed to resolve the problem. A slow release acid) was added, maintaining chlorinating agent (trichlorcyanuric concentrations of 1-3 ppm available chlorine. This reduced the count of bacteria to < 2 ml-‘, a level consistently maintained for > 1 year. The baths are now drained, cleaned and refilled at monthly intervals. Available chlorine is estimated weekly by the works department, and chlorinating agent added to the cooling bath as required. Discussion
Recommendations for the provision and equipping of a milk kitchen have been made (Bolton, 1966; Maternity Services Advisory Commitee, 1985; Hicks & MacGregor, 1968) but the needs of an individual unit will vary in accordance with the size and type of hospital. A mutual aid agreement with a neighbouring milk kitchen, to allow continued supply of feeds in the event of a breakdown, seems to us essential; these arrangements should be tested in practice. Our intention was to ensure that any single failure in procedures or equipment should be covered by good practice at every other stage, e.g., failure of pasteurization should not be disastrous, provided that feeds have acquired minimal contamination during preparation, and growth is not allowed to occur subsequently. In this, we depend on the manufacturer’s quality control of dry powder ingredients, as resources are too limited for comprehensive sampling. With this proviso, good management should, hopefully, prevent disastrous simultaneous multiple failures. However, the incident of
Milk
kitchen
review
185
contamination from the whisk clearly illustrates that problems may arise from unlikely sources: vigilance, good communications and bacteriological monitoring are required to prevent and solve such problems. Sampling provides the microbiologist with an opportunity for regular visits, to build up a good liaison with the milk kitchen staff, and to observe the production of feeds; these aspects were as important in establishing good practices as the monitoring process itself.
References Anderton, A. (1983). Microbiological aspects of the preparation and administration of nasogastric and naso-enteric feeds in hospital-A review. Human Nutrition: Applied Nutrition 37A, 426440. Ayliffe, G. A. J., Collins, B. J. & Pettit, F. (1970). Contamination of infant feeds in a Milton milk kitchen. Lancet i, 599-560. Baum, J. D., Fisher, C. & Smith, A. (1980). A Guide to Human Milk Banking. Vickers Medical, Basingstoke, U.K. Bolton, J. (1966). The infant formula room. Hospital Journal and Social Services Review February 4, 1966, 211-216. Department of Health and Social Security (1986). Health Service Catering Hygiene. HMSO, London. Gamsu, H. R., Cawdery, H. M. & Taylor C. G. (1969). Hospital milk kitchen. Lancet i, 1094-1050. Gillies, R. R. & Govan, J. R. W. (1966). Typing of Pseudomonas pyocyanea by pyocine production. Journal of Pathology and Bacteriology 91, 339-345. Hicks, M. & MacGregor, M. E. (1968). Modernising a milk kitchen. Nursing Mirror October 18, 1968, 31-33. Howie, J. (1985). The case for compulsory pasteurisation. British Medical Journal, 291, 422-423. Maternity Services Advisory Committee (MSAC) (1985). Maternity care in action part III. Care of the mother and baby. Third report of the Maternity Services Advisory Committee to the Secretaries of State for Social Services and for Wales. HMSO, London. Seldon, R., Lee, S., Wang, W. L. L., Bennett, J. V. & Eickhoff, T. C. (1971). Nosocomial klebsiella infections: intestinal colonization as a reservoir. Annals of Internal Medicine 74, 657-664. Sharpe, J. C. M., Paterson, G. M. & Barrett, N. J. (1985). Pasteurisation and the control of milkborne infection in Britain. British MedicalJournal 291, 463-464.