Nasal staphylococci and sepsis in hospital patients

Intranasal mupirocin reduces sternal wound infection after open heart surgery in diabetics and nondiabetics

BACKGROUND

This study was designed to determine whether decreasing nasal bacterial colonization by applying Mupirocin (MPN) intranasally decreases sternal wound infections.

METHODS

We prospectively followed 992 consecutive open heart surgery (OHS) patients who did not receive MPN prophylaxis (group I) from January 1, 1995 to October 31, 1996. Group II consisted of 854 consecutive patients followed prospectively from December 1, 1997 to March 31, 1999 treated with intranasal MPN given on the evening before, the morning of OHS, and twice daily for 5 days postoperatively.

RESULTS

There was a significant difference in the rate of overall sternal wound infections between the untreated (group I) and the treated group (group II): 2.7% (27 of 992) versus 0.9% (8 of 854) (p = 0.005). The difference was also significant in the diabetic subgroup: 5.1% (14 of 277) (group I) versus 1.9% (5 of 266) (group II) (p = 0.04) and the nondiabetic group: 1.8% (13 of 715) (group I) versus 0.5% (3 of 588) (group II) (p = 0.03). The cost of MPN treatment was $12.47 per patient compared with $81,018 +/- $41,567 for a deep wound infection with no antibiotic-related complications recorded.

CONCLUSIONS

Prophylactic intranasal MPN is safe, inexpensive, and very effective in reducing the overall sternal wound infections by 66.6%.

Nasal carriage of Staphylococcus aureus is a major risk factor for surgical-site infections in orthopedic surgery

OBJECTIVE

To determine the relative importance of different risk factors for the development of surgical-site infections (SSIs) in orthopedic surgery with prosthetic implants.

DESIGN

In a cohort of 272 patients, the following possible risk factors were studied: age, gender, method of hair removal, duration of operation, surgeon, underlying illness, and nasal carriage of Staphylococcus aureus. Infections were recorded following the Centers for Disease Control criteria. The relation between risk factors and SSI was tested in univariate and multiple logistic regression analysis.

SETTING

Community hospital in Breda, The Netherlands.

RESULTS

18 (6.6%) of 272 patients experienced SSI: 11 superficial and 7 deep SSI. These infections led in three cases to removal of the prosthesis and caused 286 extra days in hospital. The main causative pathogen was S aureus. In multiple logistic regression analysis, the following factors were independent risk factors for the development of SSI: high-level nasal carriage of S aureus (P=.04), male gender (P=.005), and surgeon 1 (P=.006). The only independent risk factor for SSI with S aureus was high-level nasal carriage of S aureus (P=.002).

CONCLUSION

High-level nasal carriage of S aureus was the most important and only significant independent risk factor for developing SSI with S aureus.

The endogenous pathway is a major route for deep sternal wound infection

OBJECTIVE

Deep wound infections pose an increasing problem in cardiac surgery patients. Prospective infection monitoring is thus a means of identifying possible risk factors.

METHODS

Within a period of 5 months, a total of 376 adult patients, 260 men and 116 women, with a mean age of 62.6 years (range 18-88), underwent coronary bypass grafting (n=281) or other cardiac surgery procedures (n=95). Nasal cultures were taken preoperatively from every patient, as well as cultures of the wound during surgery and when dressings were changed thereafter. In addition, nasal cultures were taken from all the medical and nursing staff. To differentiate endogenous and exogenous infection pathways, DNA fingerprint analysis was performed.

RESULTS

A total of 38 patients (10.1%) developed a wound infection, in 14 patients this happened to be a deep wound infection, in 24 patients a superficial one. Five sternal wound infections were associated with mediastinitis (1.3%). The occurrence of a wound infection overall resulted in prolonged hospitalization (29.4+/-24 vs. 11.9+/-6.9 days, P=0.001), but not in increased hospital mortality (4.4% vs. 3.9%). Obesity, diabetes mellitus and nasal carriage of Staphylococcus aureus proved to be independent risk factors with an odds ratio of 2.07, 2.26 and 2.28, respectively. In all but one of the sternal colonizations with S. aureus, DNA fingerprint analysis demonstrated an identical pattern of S. aureus from the patient's nose and sternum, indicating an endogenous infection pathway.

CONCLUSIONS

The determination of the endogenous pathway for severe wound infection makes prevention possible by means of preoperative local S. aureus eradication.

Sources of staphylococcal infection in surgical wound sepsis

1. In two hospitals, post-operative staphylococcal wound sepsis occurred with equal frequency in patients who were and in those who were not nasal carriers of Staph. aureus.

2. Nasal carriage of Staph. aureus was not always associated with skin carriage at the site of operation, but even patients who were skin carriers suffered no more sepsis than non-carriers.

3. Self-infection was a less frequent cause of sepsis than was cross-infection. Other investigations of this type have revealed conflicting findings on the frequency of self-infection. These may be due to differences in the epidemiological properties of staphylococci infesting the hospitals; to different methods of preoperative skin preparation; and to the different types of operation concerned.

4. In one of the hospitals, 31% of probable operating-room infections were with organisms similar to those carried by some member of the surgical team. In infections thought to have occurred in the ward, only 10% showed this similarity. In 11 of 35 presumed operating-room infections, the source may have been a member of the surgical team.

For help and co-operation we are grateful to Mr G. A. Mason, Senior Surgeon, Newcastle Regional Thoracic Surgery Service; and Dr Joan Millar, Miss G. Jones, Miss E. Smith, Mrs Jean Best, Miss Winifred Mahon, Dr K. Hodgkin, Dr W. Stewart, Mr S. Griffin, Mr W. C. Barnsley, Mr R. Dobson, Mr W. H. Bound, and many nurses and other hospital workers. Our especial thanks are due to Professor R. E. O. Williams, who phage-typed many of the staphylococci, and then taught us to do this for ourselves.

Effect of Naseptin cream prophylaxis on staphylococcal infection in adult surgical wards and infant nurseries

A controlled trial of Naseptin cream, as an anti-staphylococcaiprophylactic, made in two adult wards, showed the cream to be effective in reducing nasal carriage, including antibiotic resistant strains. There was no marked effect on wound infection.

A controlled trial of Naseptin cream and Sterzac powder prophylactically in maternity nurseries was found to be effective in reducing nasal carriage and infection.

These findings are discussed, and recommendations on the use of Naseptin cream as a prophylactic are made.

The nose: an underestimated source of Staphylococcus aureus causing wound infection

For the last fifty years, the nose has been intermittently recognized and targeted as a source of Staphylococcus aureus causing surgical site infection. In London in 1959, Williams and co-workers established for the first time that nasal carriers had increased rates of surgical sepsis compared with non-carriers. For half of these patients, the source was the patient's own nose. Post-admission acquisition of tetracycline-resistant strains was associated with even higher rates of infection. The increasing appearance of epidemic methicillin-resistant S. aureus (MRSA) in the 1980s rekindled interest in these (largely overlooked) studies, when the elimination of nasal carriage by topical mupirocin proved pivotal for the control of MRSA in Northern Europe and elsewhere. In the late 1980s and 1990s, Boelaert, Holton and others, appreciating the work performed forty years previously, used nasal mupirocin for the successful prevention of sepsis with S. aureus in patients on haemodialysis and continuous ambulatory peritoneal dialysis without incurring problems with mupirocin resistance. In 1995, Kluytmans and colleagues demonstrated that nasal carriage of S. aureus is a significant risk factor for wound infection after cardiac surgery. Towards the year 2000, the use of prophylactic nasal mupirocin for the prevention of serious sepsis in major clean surgery is emerging as a plausible and exciting new strategy.

Reduction of surgical site infections in major surgery by elimination of nasal carriage of Staphylococcus aureus

Staphylococcus aureus has long been recognized as an important pathogen in human disease. Staphylococcal infections occur regularly in hospital patients and, despite antibiotic therapy, have severe consequences. An increasing number of such infections are caused by methicillin-resistant S. aureus (MRSA) strains, many of which have become multi-resistant to treatment. In an unblinded intervention trial, with historical controls, perioperative nasal carriage of S. aureus was eliminated using mupirocin nasal ointment. A significant reduction in surgical site infection was observed post-intervention in the treated group of patients. No resistant to mupirocin was observed. The results of this study warrant a prospective randomized, placebo-controlled study to confirm the efficacy of mupirocin.

New approaches to reduce Staphylococcus aureus nosocomial infection rates: treating S. aureus nasal carriage

BACKGROUND

Nosocomial infections cause significant patient morbidity and mortality. The 2.5 million nosocomial infections that occur each year cost the US healthcare system $5 million to $10 million. Staphylococcus aureus has long been recognized as an important pathogen in human disease and is the most common cause of nosocomial infections.

OBJECTIVE

To describe the epidemiology of S. aureus nosocomial infections that are attributable to patients' endogenous colonization.

DATA SOURCES

Review of the English-language literature and a MEDLINE search (as of September 1997).

DATA SYNTHESIS

The ecologic niche of S. aureus is the anterior nares. The prevalence of S. aureus nasal carriage is approximately 20-25%, but varies among different populations, and is influenced by age, underlying illness, race, certain behaviors, and the environment in which the person lives or works. The link between S. aureus nasal carriage and development of subsequent S. aureus infections has been established in patients on hemodialysis, on continuous ambulatory peritoneal dialysis, and those undergoing surgery. S. aureus nasal carriers have a two-to tenfold increased risk of developing S. aureus surgical site or intravenous catheter infections. Thirty percent of 100% of S. aureus infections are due to endogenous flora and infecting strains were genetically identical to nasal strains. Three treatment strategies may eliminate nasal carriage: locally applied antibiotics or disinfectants, systemic antibiotics, and bacterial interference. Among these strategies, locally applied or systemic antibiotics are most commonly used. Nasal ointments or sprays and oral antibiotics have variable efficacy and their use frequently results in antimicrobial resistance among S. aureus strains. Of the commonly used agents, mupirocin (pseudomonic acid) ointment has been shown to be 97% effective in reducing S. aureus nasal carriage. However, resistance occurs when the ointment has been applied for a prolonged period over large surface areas.

CONCLUSIONS

Given the importance of S. aureus nosocomial infections and the increased risk of S. aureus nasal carriage in patients with nosocomial infections, investigators need to study cost-effective strategies to prevent certain types of nosocomial infections or nosocomial infections that occur in specific settings. One potential strategy is to decrease S. aureus nasal carriage among certain patient populations.

Risk factors for developing clinical infection with methicillin-resistant Staphylococcus aureus (MRSA) amongst hospital patients initially only colonized with MRSA

In hospital outbreaks of methicillin-resistant Staphylococcus aureus (MRSA) many patients are initially colonized without infection. The reasons why some progress to infection while others do not are not known. A cohort of 479 hospital patients, initially only colonized with MRSA, was followed prospectively for the development of MRSA infection. Risk factors for progression to infection were assessed using Cox proportional hazards survival analysis. Fifty-three patients (11.1%) developed 68 MRSA infections. Intensive care setting, administration of three or more antibiotics, ulcers, surgical wounds, nasogastric or endotracheal tubes, drains, and urinary or intravenous catheterization were all associated with increased rates of MRSA infection. Multivariate analysis showed that intensive care patients, compared with medical patients, had a higher rate of developing MRSA infection within the first four days of admission, with a hazard ratio of 26.9 (95% CI 5.7-126). Surgical wounds, pressure ulcers and intravenous catheterization were also independent risk factors, with hazard ratios (and 95% CI) of 2.9 (1.3-6.3); 3.0 (1.6-5.7) and 4.7 (1.4-15.6), respectively. These findings suggest that, during an MRSA outbreak, clinical infection would be reduced if surgical and intensive care patients received priority for the prevention of initial colonization with MRSA. Prevention of pressure ulcers, and strict aseptic care of intravenous catheters and surgical wounds would also reduce the development of MRSA infection. Since early treatment with vancomycin is known to reduce the mortality, patients colonized with MRSA who also have one or more of these risk factors may warrant empirical vancomycin therapy at the earliest suggestion of infection.

Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms, and associated risks

Staphylococcus aureus has long been recognized as an important pathogen in human disease. Due to an increasing number of infections caused by methicillin-resistant S. aureus (MRSA) strains, therapy has become problematic. Therefore, prevention of staphylococcal infections has become more important. Carriage of S. aureus appears to play a key role in the epidemiology and pathogenesis of infection. The ecological niches of S. aureus are the anterior nares. In healthy subjects, over time, three patterns of carriage can be distinguished: about 20% of people are persistent carriers, 60% are intermittent carriers, and approximately 20% almost never carry S. aureus. The molecular basis of the carrier state remains to be elucidated. In patients who repeatedly puncture the skin (e.g., hemodialysis or continuous ambulatory peritoneal dialysis [CAPD] patients and intravenous drug addicts) and patients with human immunodeficiency virus (HIV) infection, increased carriage rates are found. Carriage has been identified as an important risk factor for infection in patients undergoing surgery, those on hemodialysis or CAPD, those with HIV infection and AIDS, those with intravascular devices, and those colonized with MRSA. Elimination of carriage has been found to reduce the infection rates in surgical patients and those on hemodialysis and CAPD. Elimination of carriage appears to be an attractive preventive strategy in patients at risk. Further studies are needed to optimize this strategy and to define the groups at risk.

Methicillin-resistant Staphylococcus aureus in nursing homes. Epidemiology, prevention and management

Infections caused by Staphylococcus aureus are a significant cause of morbidity and mortality in elderly persons in the community, hospitals and chronic care facilities. Methicillin-resistant S. aureus (MRSA) has become an important cause of severe infection in acutely ill patients in hospitals from diverse geographic areas. Whether MRSA has the same potential to spread and cause infection in nursing homes has only recently been explored. In the facilities studied, asymptomatic MRSA carriage has been common, but patients do not appear to have the same risk of acquiring the organism. The risk of MRSA colonisation appears to be associated with increasing debility, the presence of invasive devices or wounds, and increased overall mortality. Most nursing home residents acquire MRSA during a hospital stay, not in the nursing home. Transmission of MRSA between nursing home residents may be less efficient than that seen among hospitalised patients. Once residents acquire MRSA, they remain persistently colonised for months to years. Many different MRSA strains circulate within nursing homes, probably reflecting the strains found in referring hospitals. Fortunately, although MRSA colonisation is relatively common, rates of MRSA infection and attributable mortality appear to be low. However, the presence of MRSA in a facility might lead to fewer treatment options when infections do occur, with more adverse effects and increased costs. The routine use of surveillance cultures and antibacterials in an attempt to permanently eradicate MRSA from nursing home residents has not been successful, and resistance has quickly emerged. More importantly, nursing homes should utilise infection control practices that disrupt transmission by direct contact, thus preventing the potential spread of MRSA. Simple, inexpensive precautions, which emphasise handwashing and the use of gloves and gowns when soiling by patient body fluids is likely, are generally effective. Knowledge of the patient's MRSA colonisation status is not necessary when these universal barrier precautions are applied to the care of all patients. If an increase in the rate of MRSA infections is documented, more intensive infection control measures should be implemented.

NASAL CARRIAGE OF STAPHYLOCOCCI AND POST-OPERATIVE STAPHYLOCOCCAL WOUND INFECTION

One hundred patients undergoing major surgical operations in a provincial group hospital were studied bacteriologically daily to determine any relation between nasal carriage of staphylococci and post-operative staphylococcal wound sepsis.Sixty-four patients were either carriers on admission and throughout their stay, or their noses became colonized at some time by ward strains. Six cases of staphylococcal wound or drain wound sepsis occurred in this group, four due to ward strains and two to the patient's own nasal strain. Four patients lost the nasal strain after admission and thereafter their noses remained free from staphylococci. There was no sepsis among these. Thirty-two patients never carried staphylococci in their noses at any time. There was no wound sepsis in this group but in two patients the drain wounds became infected with ward strains. Grouping all cases of staphylococcal wound or drain wound sepsis there were three times as many caused by ward strains as by nasal strains. In 10 of the 11 cases of wound or drain wound sepsis, including three cases due to Gram-negative bacteria, a physical cause in the shape of a drain, necrosis of skin edges, or loss of tissue was present, providing an entry for bacteria.

Preoperative bacterial colonization and its influence on postoperative wound infections in plastic surgery

During two separate periods a total of 654 patients were included in a clinical study relating preoperative bacterial colonization to occurrence of postoperative wound infection in plastic surgery. During the second period one half of the patients were randomized to receive prophylactic azithromycin. Bacteriological samples were collected from the nasal vestibulum during both periods, and additionally from the surgical field during the second period. All patients had preoperative chlorhexidine bathing. The bacteriological findings were categorized as either normal flora or potentially pathogenic bacteria, and as either having no growth. Surgical wounds were divided into four contamination classes. Postoperative follow-up was 30 days, and assessment of wound infection was based on a graded scale. We did not find any statistically significant relation between preoperative bacterial colonization and postoperative wound infection, regardless of place of sample collection, method of bacterial classification, class of contamination or use of prophylactic azithromycin.

STAPHYLOCOCCI IN NOSES AND STREPTOCOCCI IN THROATS OF ISOLATED AND SEMI-ISOLATED ANTARCTIC COMMUNITIES

The Antarctic provides unusually simplified conditions for the study of the persistence and exchange of micro-organisms of the upper respiratory tract. The work reported here was done while the author was in the Falkland Islands Dependencies Survey and the United States Antarctic Research Program.

Staph, aureus and Staph, albus persisted in the noses, and a-haemolytic streptococci in the throats of men throughout long periods of isolation and semi-isolation in Antarctica.

On the whole, men kept their own strains (phage types) of Staph, aureus despite living in very close contact with each other.

Persistent carriers of Staph, aureus (90% or more positive swabs per individual) continued to carry this organism for as long as 2 years in Antarctica. Data from men at Wilkes and Hallett IGY Stations indicated that there was a decrease in the intermittent and occasional carrier rates, resulting in a much lower total carrier rate after 12 months Antarctic isolation.

Evidence is presented to suggest that β-haemolytic streptococci had disappeared from throats after 12 months of isolation. It is thought that the absence of upper respiratory infections in these communities is due to absence of the bacterial or viral agents.

There is an urgent need for further work on the carriage of micro-organisms in the present unique epidemiological conditions of the Antarctic, and for better laboratory facilities there.

Sternal wound infection after heart operations in pediatric patients associated with nasal carriage of Staphylococcus aureus

A cluster of six pediatric cases of deep-seated Staphylococcus aureus infection after heart operations prompted us to perform molecular typing of the S. aureus isolates by pulsed-field gel electrophoresis. This revealed the presence of genotypically distinct isolates in four of the six patients. Isolates of two patients were genotypically identical. All patients carried S. aureus in the anterior nares. In each patient, the banding pattern of deoxyribonucleic acid in these isolates was indistinguishable from that in strains isolated from blood or wound cultures. Molecular typing with pulsed-field gel electrophoresis ruled out nosocomial transmission of S. aureus between four patients; at the same time, it provided evidence for an association between nasal colonization and postoperative wound infection. Epidemiologic investigation of potential links between two patients with identical isolates did not provide any evidence for nosocomial transmission of S. aureus between these patients. Because nasal colonization with S. aureus may be a risk factor for surgical wound infection in pediatric patients undergoing heart operations, preoperative decolonization appears to be warranted.

The significance of nasal carriage of Staphylococcus aureus and the incidence of postoperative wound infection

Staphylococcus aureus infections are associated with considerable morbidity and, in certain situations, mortality. The association between the nasal carriage of S. aureus and subsequent infection has been comprehensively established in a variety of clinical settings, in particular, patients undergoing haemodialysis and continuous ambulatory peritoneal dialysis (CAPD), and in patients undergoing surgery. Postoperative wound infections are associated with a high degree of morbidity and represent an important medical issue. Until recently, eradication of S. aureus nasal carriage by various topical and systemic agents had proved unsuccessful. Mupirocin is a novel topical antibiotic with excellent antibacterial activity against staphylococci. Recent studies have demonstrated that intranasal administration of mupirocin is effective in eradicating the nasal carriage of S. aureus and in reducing the incidence of S. aureus infections in haemodialysis and CAPD patients. It has been suggested that sufficient evidence now exists to test the hypothesis that eradication of the carrier state in surgical patients preoperatively may reduce the incidence of S. aureus postoperative wound infections.

Nasal carriage of Staphylococcus aureus and cross-contamination in a surgical intensive care unit: efficacy of mupirocin ointment

A six month prospective study was carried out in a surgical intensive care unit (SICU) of a university hospital to assess the incidence and routes of exogenous colonization by Staphylococcus aureus. A total of 157 patients were included in the study. One thousand one hundred and eleven specimens (nasal, surgical wound swabs, tracheal secretions obtained on admission and once a week thereafter, and all clinical specimens) were collected over a four month period from patients without nasal decontamination (A). They were compared with 729 specimens collected over a two month period from patients treated with nasal mupirocin ointment (B). All S. aureus strains were typed by restriction fragment length polymorphism (RFLP) pulsed-field gel electrophoresis after SmaI macrorestriction. The nasal colonization rates on admission were 25.5 and 32.7% in groups A and B, respectively. Thirty-one untreated patients (31.3%) and three patients (5.1%) treated with nasal ointment, acquired the nasal S. aureus in the SICU (P = 0.00027). Nasal carriers were more frequently colonized in the bronchopulmonary tract (Bp) and surgical wound (Sw) (62%) than patients who were not nasal carriers (14%) (P < 0.00001). The patterns were identical for nasal, Bp and Sw strains from the same patient. RFLP analysis characterized seven epidemic strains of methicillin-resistant S. aureus (MRSA) which colonized 60% of group A and 9% of group B patients (P < 0.00001). The bronchopulmonary tract infection rate was reduced in group B (P = 0.032). In conclusion, in an SICU, nasal carriage of S. aureus appeared to be the source of endogenous and cross-colonization. The use of nasal mupirocin ointment reduced the incidence of Bp and Sw colonization, as well as the MRSA infection rate.

Surveillance of postoperative infections in thoracic surgery

Postoperative infections (PIs) are serious complications of thoracic surgery. To gain insight into the nature and the scope of the problem, an 18-month prospective surveillance was conducted at the department of thoracic surgery of the University Hospital Rotterdam, Dijkzigt. PI were classified according to CDC criteria. One hundred and ninety-four out of 983 patients (19.7%) developed one or more PIs and in these 194 patients, 268 PIs were diagnosed. The incidence of PI was 2.0 per 100 days of postoperative stay. The mean postoperative length of stay (LOS) of the 194 patients with PI was 14.1 days longer than those without PI. Deep surgical wound infections (DSWIs) were associated with the longest prolongation of the median postoperative LOS in the hospital (30 days longer). Although lower than DSWIs, incisional surgical wound infections also had a significant prolongation of stay (median 10 days longer). Staphylococcus aureus was the most important pathogen associated with surgical wound infections (SWIs). Phage typing of 29 strains causing SWI showed only two identical pairs, so only a minority of infections could be explained by cross-infection. Older age, and more complicated procedures (e.g. cardiac valve operations) were independent, statistically significant, risk factors for the development of PI. Since there is a progressive trend towards operating on older patients and performing more complicated procedures, the incidence of PI is expected to increase. Therefore it will become increasingly important to develop new strategies to prevent these serious complications.

Prospective study of infection, colonization and carriage of methicillin-resistant Staphylococcus aureus in an outbreak affecting 990 patients

In the three years between November 1989 and October 1992, an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) affected 990 patients at a university hospital. The distribution of patients with carriage, colonization or infection was investigated prospectively. Nosocomial acquisition was confirmed in at least 928 patients, 525 of whom were identified from clinical specimens as being infected (n = 418) or colonized (n = 107) by MRSA. An additional 403 patients were identified from screening specimens, of whom 58 subsequently became infected and 18 colonized. Screening of the nose, throat and perineum detected 98% of all carriers. Of the 580 infections in 476 patients, surgical wound, urinary tract and skin infections accounted for 58% of the infections. Of the 476 infected patients, death was attributable to MRSA infection in 13%. Colonization with MRSA was found in 127 patients and 42% of 165 colonized sites were the skin. Auto-infection from nasal carriage or cross-infection, probably via staff hands, seemed to be the most common mode of acquisition of MRSA infections.

Nasal carriage of methicillin-resistant Staphylococcus aureus by hospital staff in north Jordan

The nasal carriage of methicillin-resistant Staphylococcus aureus was detected in 550 hospital staff members of four hospitals in north Jordan. Of the 109 (19.8%) individuals tested who were nasal carriers of S. aureus, only 32 (5.8%) were found to be carriers of methicillin-resistant Staphylococcus aureus. The carriers were four doctors, 23 nurses, three laboratory technicians, one maid and an administrator. It was noted that 25 (78.1%) of these carriers were in constant contact with patients in operating theatres, surgical wards or intensive care units. It was not clear whether the carriers were short- or long-term carriers, or whether they were persistent sources of methicillin-resistant Staphylococcus aureus. Decontamination of these carriers was considered among other control measures to avoid the dangerous outcome of hospital outbreaks caused by this potential pathogen.

A survey of nasal carriage of Staphylococcus aureus in a neonatal ward in Ile-Ife, Nigeria

The nasal carriage rate of Staphylococcus aureus among maternal-infant pairs was 18% compared with 39% among hospital staff in Ile-Ife, Nigeria during a 12-week survey. Of the newborns, 46% tested positive compared with 26% of their mothers. The S. aureus phage types recovered were predominantly of the group III type (38%); however, 28% of the strains isolated were non-typable. All the S. aureus strains were resistant to penicillin, 84% to tetracycline, and 35 and 24% were resistant to streptomycin and chloramphenicol, respectively. Altogether 19% of the strains tested were resistant to methicillin.

Resistance to vancomycin and teicoplanin: an emerging clinical problem

Vancomycin and teicoplanin are glycopeptides active against a wide range of gram-positive bacteria. For 30 years following the discovery of vancomycin in 1956, vancomycin resistance was not detected among normally susceptible bacteria recovered from human specimens. Since 1986, however, bacteria resistant to vancomycin or teicoplanin or both have been described. Strains of the genera Leuconostoc, Lactobacillus, Pediococcus, and Erysipelothrix seem inherently resistant to glycopeptides. Species and strains of enterococci and coagulase-negative staphylococci appear to have acquired or developed resistance. There are at least two categories of glycopeptide resistance among enterococci, characterized by either high-level resistance to vancomycin (MIC, greater than or equal to 64 mg/liter) and teicoplanin (MIC, greater than or equal to 8 mg/liter) or lower-level vancomycin resistance (MIC, 32 to 64 mg/liter) and teicoplanin susceptibility (MIC, less than or equal to 1 mg/liter). The two categories appear to have similar resistance mechanisms, although genetic and biochemical studies indicate that they have arisen independently. Among coagulase-negative staphylococci, strains for which vancomycin MICs are up to 20 mg/liter or teicoplanin MICs are 16 to 32 mg/liter have been reported, but cross-resistance between these glycopeptides varies. The selective advantage accorded to glycopeptide-resistant bacteria and the observation that high-level resistance in enterococci is transferable suggest that such resistance may be expected to increase in incidence. Clinicians and microbiologists need to be aware of this emerging problem.

A long-term study of the nasal carriage of Staphylococcus aureus in healthy Nigerian students

892 nasal swabs were collected from 50 pharmacy students (25 male and 25 female) over a period of 15 months. 323 (36.2%) contained Staphylococcus aureus and analysis of the results showed that 19 (38%) of the subjects were true nasal carriers of S. aureus, 23 (46%) were non-carriers, and the other 8 (16%) were sporadic non-carriers. 84% of the 162 isolates tested were resistant to penicillin and 58% were resistant to tetracycline.

Gastrointestinal carriage of methicillin-resistant Staphylococcus aureus

Nasal and rectal cultures were taken from all patients with methicillin-resistant Staphylococcus aureus identified on routine cultures obtained because of clinical indications. Of 117 patients studied over a 3-year period, 70 (60%) had rectal colonization and 62 (53%) had nasal colonization. Rectal colonization, probably reflecting gastrointestinal carriage, may be a source of transmission of methicillin-resistant S. aureus in hospitalized patients and may be difficult to eradicate.

Colonization of newly arrived house staff by virulent staphylococcal phage types endemic to a hospital environment

The acquisition of hospital strains of Staphylococcus aureus by new house officers was studied in an 800-bed referral hospital over a 1-year period. S. aureus isolates, including three strains with characteristic phage patterns that had previously been documented to cause disease in patients and colonize hospital personnel, were recovered from the anterior nares of 35 of 54 newly arrived house officers. There was a significant correlation (r = 0.7475; P less than 0.02) between colonization with the dominant hospital strain (S) and exposure to the hospital environment over 12 months. No hospital-wide increase in infections owing to the S strain was seen during this period, which suggests that house staff acquired this strain from reservoirs within the hospital. The finding of colonization with virulent endemic S. aureus strains in house officers working on every ward of the hospital suggests that new strategies for control of S. aureus nosocomial infections must be considered and evaluated.

Empirical and mathematical models on the relationship between patient age and nosocomial infection

This paper proposes two models, one a purely empirical one and the other a mathematical one, which depict the relationship between patient age and nosocomial infection rate. The empirical model is based on the two age-specific phenomena, the acquisition of resistance to infection with age mainly in the early years of life and the deterioration of existing resistance mechanisms with ageing predominantly in the later years of life. The net effect of these two factors is shown to approximate into a quadratic relationship between age and nosocomial infection rate, like the type demonstrated in earlier experimental studies. The second mathematical model is derived from studies on cancer research and here the relationship between age and nosocomial infection rate for patients in the age group 30-70 years is represented by a log linear model. The model was tested against experimental data derived from large surveys on nosocomial infection and the resulting correlation coefficient was 0.98. The model was an extremely good fit when tested against postoperative wound infection rates as well as nasal carriage rate of antibiotic resistant Staph. aureus. Furthermore, when patients in the survey were subdivided into groups of male patients and female patients and into two groups based on the type of operative wound, the model was still found to be a very good fit to the experimental data. This confirmed the validity of the model even in the presence of other patient-related parameters. Finally, the model was tested against the results of a totally different experimental study conducted elsewhere and the resulting correlation coefficient was 0.999, which confirmed the validity of the model in a universal context.

Application of deterministic epidemic theory to nasal carriage of Staphylococcus aureus

Nasal carriage of antibiotic-resistant Staphylococcus aureus is often used as an index of cross-infection in hospitals. In this paper, a deterministic model of the epidemiology of Staphylococcal nasal carriage was derived employing the concepts of epidemic theory. This theoretical model was tested against experimental data gathered from a large survey. When the association between nasal carriage of tetracycline-resistant Staphylococci and length of stay in hospital derived from the survey was compared with theoretical figures derived from the model, the validity of the model in a real situation was confirmed.

Comparison of 4% chlorhexidine gluconate in a detergent base (Hibiclens) and povidone-iodine (Betadine) for the skin preparation of hemodialysis patients and personnel

The abnormal cutaneous flora of hemodialysis (HD) patients might contribute to their frequent septic complications. We compared the effects of 13 wk of Betadine and 13 wk of Hibiclens on the skin flora of HD patients and personnel. Skin cultures were obtained weekly immediately prior to the disinfection, preceding each triweekly HD treatment, and monthly, at 2 and 4 hr postdisinfection. Total bacterial counts from predisinfection cultures were not significantly altered over either 13-wk treatment period. Hibiclens reduced total bacterial counts (p less than 0.01) and eradicated cutaneous staphylococci (p = 0.032) at both 2 and 4 hr postdisinfection significantly more than did Betadine. No reduction of staphylococcal sensitivity to either germicidal agent could be demonstrated. Neither agent was associated with severe adverse reactions and Hibiclens could not be detected in the blood. Hibiclens appears to offer short-term advantages over Betadine in the HD setting because of significantly longer duration of antibacterial activity.

Antimicrobial sensitivity patterns of hospital and non-hospital strains of Staphylococcus aureus isolated from nasal carriers

The nasal carriage rate of Staphylococcus aureus was significantly higher in hospitalized persons (children, adult females and staff) - 53.8%, - than in similar persons at a local clinic - 29.8% (P less than 0.001) - in Ile-Ife, Nigeria. However, unlike studies carried out elsewhere, a higher proportion of S. aureus strains obtained from persons at the clinic were resistant to commonly used antimicrobial agents than were strains isolated in the hospital. This has been attributed to the ease at which these drugs can be obtained by the general population and used unsupervised and indiscriminately. Methicillin was the most effective antimicrobial agent against pathologic staphylococci (2.2% resistance), followed by erythromycin (16.5% resistance), co-trimaxozole (28.0% resistance), chloramphenicol (76.9% resistance), tetracycline (78.6% resistance) and penicillin and ampicillin (97.8% resistance). The widespread resistance of S. aureus to penicillin and ampicillin (and other antimicrobial agents) is of clinical significance in the treatment of post-operative infections, since carriers are reportedly more prone to such infections than are non-carriers.

Nasal carriers of coagulase-positive staphylococci in a Nigerian hospital community

Nasal swabs taken from 324 subjects in a Nigerian hospital were examined for the presence of coagulase positive staphylococci. The subjects used in this study included the patients, staff and "auxiliaries" aged from one day to 70 years. The results obtained show that approximately 50% of all the subjects were nasal carriers of Staphylococcus aureus and that age, occupation and length of the subjects' stay in hospital had a significant effect on this figure. It was also found that there is no significant difference between the prevalence of nasal carriage of S. aureus amongst the hospital staff and the patients.