Nasal acquisition of Staphylococcus aureus in a subdivided and mechanically ventilated ward: endemic prevalence of a single staphylococcal strain

Abstract

SUMMARYAn investigation was made of nasal acquisition of Staphylococcus aureus and of staphylococcal wound sepsis in a hospital ward divided into two sections and provided with mechanical ventilation, so that there was no transfer of air from one of the sections to the other. Although the strains of S. aureus found in the air, and those colonizing the noses of patients, in the protected section could seldom be related to patients nursed elsewhere in the ward, the mechanical ventilation did not lead to any significant reduction in the degree of contamination of the air or in the rate of nasal acquisition of S. aureus.Even in the protected section, nearly 20 % of the strains of S. aureus recovered from the air could not be related to known nasal carriers. Since this proportion was nearly as great as that found in the absence of directed air-flow, it seems probable that these strains were derived either from undetected sources within the section or were dispersed from the clothes of persons who entered it.Nearly one-third of the nasal acquisitions in the ward could not be related to known nasal carriers, but about one-half of these (16 %) were probably 'spurious' and half of the remainder (8 %) could be related to strains recovered from patients' lesions or drawsheets, leaving no more than 8 % unaccounted for. A short investigation in which both drawsheet and perineal samples were examined showed that drawsheet samples did not give a reliable indication of perineal carriage unassociated with nasal carriage. During the period of the investigation, a single strain of S. aureus that was resistant to a wide range of antibiotics established itself in the ward. The most notable character of this strain was the profuse dispersion of it by carriers. As a consequence, staphylococcal wound sepsis increased, with nearly three-quarters of 0. M. LIDWELL AND OTHERS the infections attributable to this strain, and nasal carrier rates increased with length of stay in the ward, over 20 % of patients who stayed 5-6 weeks acquiring the strain.

Nasal acquisition of Staphylococcus aureus in partly divided wards

“…3). As in the previous studies in which this method of analysis was employed (Lidwell et al 1966;Lidwell et al 1970) the overall risk of nasal acquisition increases much less than proportionally to the increase in exposure and is considerably greater for a given airborne exposure in the case of the tetracyclineresistant strains. The slope of the line drawn in the Fig.…”

The control by ventilation of airborne bacterial transfer between hospital patients, and its assessment by means of a particle tracer: III. Studies with an airborne-particle tracer in an isolation ward for burned patients

“…Because of this it is necessary to derive average values of ac'. To estimate the average cross-infection risks of all the rooms, the logarithmic mean of ac' at the different points was used since the risk of nasal acquisition (and hence the risk of infection) is probably more nearly related to the logarithm of the concentration of bacteria in the air (Lidwell, 1963;Lidwell et al 1971) than to the arithmetic value. To compare the results with theory it is best to take an arithmetic average of the particle concentrations at the sampling points, i.e.…”

Dispersal and transfer ofStaphylococcus aureusin an isolation ward for burned patients

“…If this can be interpreted as the extent to which the staff acquire nasal strains as a result of airborne dispersal by infected patients, it is of some interest to note that the slope is similar to that reported for nasal acquisition of Staph. aureus by patients in hospital wards (Lidwell et al 1966(Lidwell et al , 1970(Lidwell et al , 1971.…”