Incidence and persistence of Staphylococcus aureus nasal colonization in a community sample of HIV-infected and -uninfected drug users.

A longitudinal study of 282 community-based drug users was conducted from February 1999 through September 2000. Both the incidence (15.0 cases per 100 person-years at risk; 95% confidence interval, 10.2-20.7 cases per 100 person-years at risk) and persistence of Staphylococcus aureus carriage were increased among human immunodeficiency virus (HIV)-seropositive individuals.

Cellular coating of the left ventricular assist device textured polyurethane membrane reduces adhesion of Staphylococcus aureus.

OBJECTIVE: Infections are among the most common and serious complications of ventricular assist device implantation. These infections generally occur within the first 2 months after surgery. The basis for this high incidence of infection is not well established, so a murine intravascular infection model was developed with aortic implantation of the textured polyurethane patch material currently used in HeartMate ventricular assist devices (Thoratec Corporation Pleasanton, Calif). METHODS: Polyurethane patch material was placed in the wall of the mouse descending aorta. Mice were then infected with Staphylococcus aureus 1 or 14 days after implantation. In vitro adhesion studies were conducted with polyurethane membranes coated with endothelial cells and membranes coated with fibrinogen. RESULTS: Mice were susceptible to infection in both dose- and time-dependent fashions. The patch material was significantly more susceptible to infection at day 1 than day 14. Immunohistologic and morphologic studies demonstrated that the CD31+ cells deposited on the membrane surface phenotypically appeared to be endothelial cells. In vitro adhesion studies of polyurethane membranes coated with endothelial cells showed them to be less susceptible to S. aureus binding than were membranes coated with fibrinogen. CONCLUSION: Textured polyurethane membranes are less susceptible to infection as cellular deposition occurs. The time frame within which these membranes become populated with cellular material is consistent with the time-dependent clinical incidence of infection. Cellular coating of polyurethane may provide a strategy for reducing the risk of infection.

Staphylococcus aureus colonization and the risk of infection in critically ill patients.

OBJECTIVE: To evaluate the relationship between Staphylococcus aureus nasal and tracheal colonization and infection in medical intensive care unit (MICU) patients. The primary outcome was the incidence of S. aureus infection in colonized versus non-colonized patients. DESIGN: Prospective, observational cohort study. Patients admitted to the MICU during the study period were screened for S. aureus nasal and tracheal colonization by culture and a PCR assay twice weekly. Demographic, clinical, and microbiologic data were collected in the MICU and for 30 days after discharge. PFGE and antibiotic susceptibility testing were performed on all S. aureus nasal, tracheal, and clinical isolates. RESULTS: Twenty-three percent of patients (47 of 208) were nasally colonized with S. aureus. Twenty-four percent of these patients developed S. aureus infections versus 2% of non-colonized patients (P < .01). Nine of 11 patients with both nasal colonization and infection were infected by their colonizing strain. Two of 47 nasally colonized patients developed an infection with a different strain of S. aureus. Fifty-three percent of intubated patients with nasal colonization (10 of 19) had tracheal colonization with S. aureus as opposed to 4.9% of intubated, non-colonized patients (3 of 61) (P < .01). Parenteral antibiotics were ineffective at clearing nasal colonization. PCR detected S. aureus colonization (nasal and tracheal) within 6.5 hours with a sensitivity of 83% and a specificity of 99%. CONCLUSIONS: The incidence of S. aureus infection was significantly elevated in nasally colonized MICU patients. Techniques to rapidly detect colonization in this population may make targeted topical prevention strategies feasible.

A molecular epidemiological analysis of 2 Staphylococcus aureus clonal types colonizing and infecting patients with AIDS.

BACKGROUND: Persons with acquired immune deficiency syndrome (AIDS) who use drugs appear to be at increased risk for colonization and infection with Staphylococcus aureus. Little is known about the nature of and risk factors responsible for this association. This study is among the first to prospectively follow carriage and infection in this uniquely high-risk population. METHODS: We prospectively followed the cases of 75 patients with AIDS in a residential drug treatment facility and screened for S. aureus nasal colonization and infection. RESULTS: Thirty-seven baseline cultures (49%) were positive for S. aureus, and 81% of subjects were colonized at least once during the study. Thirteen subjects experienced 17 infections. Pulsed-field gel electrophoresis and sequence-based typing methods revealed that 244 (92%) of the isolates belonged to either clonal type A or B. Clonal type A was methicillin-susceptible. Clonal type B consisted of 3 main subtypes (B1, B2, and B3), all with the same allelic profile (ST8) and staphylococcal protein A gene (spa) type (7). Of note, subtype B1 was methicillin-susceptible (ST8 and spa type 7), lacking mecA, whereas the other B clones were methicillin-resistant. Both clones were resistant to trimethoprim-sulfamethoxazole. Clonal type B isolates were relatively resistant, suggesting prior exposure to the health care setting. CONCLUSIONS: This study demonstrates a sustained high rate of S. aureus carriage and infection. It demonstrates the capacity of unique methicillin-resistant S. aureus clones with an established linkage to earlier outbreaks of methicillin-resistant S. aureus, as well as to human immunodeficiency virus--infected subjects, to persist in this residential setting. It also illustrates the apparent genetic instability or transmissibility of the staphylococcal chromosomal cassette mec type IV element.

The clonality of Staphylococcus aureus nasal carriage.

Nasal carriage of Staphylococcus aureus is often a prelude to infection with the same strain. The prevailing assumption has been that colonized individuals carry a single strain. The present study investigated the frequency of simultaneous nasal carriage of multiple strains of S. aureus. Three bacterial colonies from plated samples from colonized subjects were initially compared by pulsed-field gel electrophoresis. Fourteen of 148 S. aureus-positive samples demonstrated at least a difference of a single band; 7 of these 14 samples contained different strains, and 3 of these 7 also belonged to different accessory gene regulator (agr) types. The remaining 7 samples contained clonally related isolates; 3 of these 7 contained pairs that differed by the presence or absence of the staphylococcal chromosomal cassette mec type IV. A mathematical model that we developed predicted that approximately 6.6% of S. aureus-colonized individuals carry >1 strain. The present study demonstrates that carriage of discordant S. aureus strains in individuals with nasal colonization occurs regularly and suggests that the nares are likely sites for horizontal genetic exchange among strains.

Strains of Staphylococcus aureus obtained from drug-use networks are closely linked.

Drug users have a higher incidence of colonization with Staphylococcus aureus than does the general population, and, as a result, they are at increased risk of infection with their colonizing strain. The purpose of this study was to examine the role of drug-use risk networks in S. aureus transmission, the similarity of S. aureus isolates within these networks, and the possible role of inhalation drug use paraphernalia in the transmission of S. aureus. Strains of S. aureus are shared among colonized inhalation drug users within drug-use risk networks. It suggests that patterns of drug use and the geographic location where drug sharing occurs are major contributors to the transfer of staphylococci and, as a result, to the high prevalence of staphylococcal colonization and perhaps disease in this population.

Differences between Staphylococcus aureus isolates from medical and nonmedical hospital personnel.

It is unclear whether the levels of Staphylococcus aureus colonization of hospital personnel with patient exposure are increased or whether personnel become colonized with more antibiotic-resistant strains. Differences in nasal and hand carriage of S. aureus between medical and nonmedical hospital personnel were examined. No differences in nasal carriage between the two groups were found; however, there was a trend that suggested differences in the rates of hand carriage of S. aureus (18% of nonmedical personnel and 10% of medical personnel). Medical personnel were colonized with more antibiotic-resistant isolates than nonmedical personnel (mean, 2.8 versus 2.1 isolates [P < 0.03]), and the strain profiles indicated that they tended to be more clonal in origin, suggesting that exposure to hospital isolates alters the colonization profile.

Manejo del absceso hepático / Handling of the hepatic abscess

Revisa las características de presentación clínica del absceso hepático, analiza los resultados del tratamiento implementado en la II Cátedra de Clínica Quirúrgica del Hospital de Clínicas