Hospital infection caused by non-typable Staphylococcus aureus: application of reverse typing

Hospital infections in Spain. I. Staphylococcus aureus (1978-91)

This study was undertaken to determine the distribution of phage types of Staphylococcus aureus isolates from hospital outbreaks or sporadic cases received in our laboratory during the past 14 years. The records for 15,803 isolates from 55 Spanish hospitals have been analysed. In relation to sporadic isolates we have been able to detect the predominance of phage group I and non-typable staphylococcal strains. Since 1989, we have observed a considerable increase in hospital infection caused by methicillin-resistant S. aureus strains which we could differentiate in to two groups; one belonging to phage group III (6/47/54/75/77/84/85) and other groups of nontypable strains which could be classified as phage group I-III after heat treatment (29/77/84) and with similar patterns by reverse typing (6/47/53/54/75/83A/84/85/W57/1030/18042). During 1990 and 1991, these strains have extended widely to at least six different autonomous regions creating an epidemic situation in Spain.

An outbreak of pemphigus neonatorum

During the summer of 1987, an epidemic of pemphigus neonatorum took place at Guy's Hospital. It involved more than 80 neonates in the maternity unit. Swabs from the umbilical stumps of the babies and from the noses of several attending midwives yielded Staphylococcus aureus of phage-type Group II 3A/3C. Despite an extensive disinfection policy, which included identification and treatment of carriers, the outbreak persisted for 3 months. Final resolution came only after detailed epidemiological research revealed those midwives most likely to be involved. After these had been singled out for further treatment, the outbreak ended. The epidemic strains were later subjected to reverse phage-typing, plasmid profiling and in vivo testing for production of epidermolytic toxin in order to confirm true carriers and cases. Retrospective analysis identified those persons most likely to have been responsible for propagation of the epidemic strain. The exact course of the outbreak was then clarified.

Heat treatment to increase phage typability of Staphylococcus aureus

Heat treatment was used to reduce the number of Staphylococcus aureus strains that were not typable with the basic set of phages. All strains were phage typed according to the standard method after growth in broth at 37 degrees C or 48 degrees C. Forty-eight of 72 nontypable strains could be phage typed after heat treatment of the bacterial cultures. The page lysability increased with the higher incubation temperature of the broth, but the mean variability in the phage pattern of a strain was not significantly affected. The phage typing results of strains sampled over a period of several months were in accordance with the epidemiology, suggesting that phage typing after incubation at 48 degrees C is a stable and useful epidemiological tool.

Outbreak of staphylococcal scalded skin syndrome among neonates

Over a period of 2 months, 12 babies born in the maternity unit at Guy's Hospital developed staphylococcal scalded skin syndrome in two distinct outbreaks. Staphylococci isolated from the babies, together with those from the mothers and attending medical staff were phage-typed. All isolates from the babies were of type 3A/3C. During the first outbreak only one carrier of the epidemic strain (a paediatrician) was found but a further 12 persons were identified as possible carriers during the second outbreak. In order to confirm the link between outbreaks, all phage group II isolates were subjected to reverse phage-typing, testing for metal-ion resistance, plasmid profiling and in-vivo testing for production of epidermolytic toxin. It was shown that the same epidemic strain of toxin-producing Staphylococcus aureus was responsible for both outbreaks. The affected neonates responded rapidly to a short course of intravenous flucloxacillin. The outbreak ceased after appropriate treatment of all carriers and the implementation of an extensive disinfection policy within the maternity unit.

Characterization of non-typable strains of Staphylococcus aureus from cases of hospital infection

A high percentage of non-typable (NT) Staphylococcus aureus strains was isolated in Spanish hospitals during 1984 and 1985. Several alternative methods of typing were employed to study these isolates. These were: phage-typing at 1000 X RTD, phage-typing after heat-treatment (48 degrees C), thermal shock (56 degrees C), reverse-typing and induction of additional phages. Using these methods the number of NT isolates was reduced by 60%. Best results were obtained with heat-treatment. Additional phages and reverse-typing were also useful. A scheme for the study of outbreaks and sporadic cases caused by NT strains is proposed using the methods described.

Phage-typing of Staphylococcus aureus from cases of bacteraemia

Isolates of Staphylococcus aureus from 98 cases of bacteraemia from 16 different hospitals were phage-typed. Fifty-six isolates were associated with sporadic infections and 42 with hospital outbreaks. In the sporadic cases, group I strains, particularly types 29, 52, or 29/52, were very frequent (39.2%), followed by non-typable strains. Type 94/96 was also common (14.2%). In hospital outbreaks, mixed I and III strains (multiply-resistant) were found in 73.6% and non-typable strains in 21.4%.