Staphylococcus aureus nasal carriage as a marker for subsequent staphylococcal infections in intensive care unit patients.
ABSTRACT From January to December 1994, 752 consecutive patients admitted to intensive care units (ICU) for more than two days were studied prospectively for Staphylococcus aureus colonization and infection. Nasal swabs were obtained at admission and weekly during the ICU stay. At ICU admission 166 patients (22.1%) were Staphylococcus aureus nasal carriers, while 586 were free of nasal colonization. Of the 166 nasal carriers, 163 harbored methicillin-sensitive Staphylococcus aureus (MSSA) and three methicillin-resistant Staphylococcus aureus (MRSA). During the ICU stay 24 of the 586 noncolonized patients became nasal carriers (11 MSSA and 13 MRSA), and one nasal carrier initially colonized by MSSA was reconlonized by MRSA. Staphylococcal infections were documented in 51 (6.8%) of the total 752 patients. After 14 days of ICU stay, the probability of developing staphylococcal infections was significantly higher for those patients who were nasal carriers at ICU admission than for those found to be initially negative (relative risk 59.6, 95% CI 20.37-184.32; p < 0.0001). In patients with ICU-acquired nasal colonization, most infections were documented prior to or at the time of the detection of the nasal colonization; thus, in this group of patients nasal carriage showed a lower predictive value for subsequent Staphylococcus aureus infections that that described classically. Paired isolates of nasal colonizing and clinical strains were studied by pulsed-field gel electrophoresis (PFGE) and mecA polymorphism analysis in 30 patients; identity was demonstrated in all but two patients. The results suggest that, outside the setting of an outbreak of MRSA, the detection of Staphylococcus aureus nasal carriers on admission may be particularly useful in identifying those patients who are at high risk for developing staphylococcal infections during their ICU stay.
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ABSTRACT: In apparent contrast to its invasive potential Staphylococcus aureus colonizes the anterior nares of 20-80% of the human population. The relationship between host and microbe appears particularly individualized and colonization status seems somehow predetermined. After decolonization, persistent carriers often become re-colonized with their prior S. aureus strain, whereas non-carriers resist experimental colonization. Efforts to identify factors facilitating colonization have thus far largely focused on the microorganism rather than on the human host. The host responds to S. aureus nasal colonization via local expression of anti-microbial peptides, lipids, and cytokines. Interplay with the co-existing microbiota also influences colonization and immune regulation. Transient or persistent S. aureus colonization induces specific systemic immune responses. Humoral responses are the most studied of these and little is known of cellular responses induced by colonization. Intriguingly, colonized patients who develop bacteremia may have a lower S. aureus-attributable mortality than their non-colonized counterparts. This could imply a staphylococcal-specific immune "priming" or immunomodulation occurring as a consequence of colonization and impacting on the outcome of infection. This has yet to be fully explored. An effective vaccine remains elusive. Anti-S. aureus vaccine strategies may need to drive both humoral and cellular immune responses to confer efficient protection. Understanding the influence of colonization on adaptive response is essential to intelligent vaccine design, and may determine the efficacy of vaccine-mediated immunity. Clinical trials should consider colonization status and the resulting impact of this on individual patient responses. We urgently need an increased appreciation of colonization and its modulation of host immunity.Frontiers in Immunology 01/2014; 4:507. DOI:10.3389/fimmu.2013.00507
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ABSTRACT: Methicillin-resistant Staphylococcus aureus is a cause of lower respiratory tract infections, particularly health care- and ventilator-associated pneumonia. Although many health systems use nasal screening for this microorganism for infection control, correlation between nasal carriage of the organism and development of infections due to it is not clear. Records of patients admitted to medical intensive care between January 1, 2011, and December 31, 2012, were reviewed retrospectively. Patients' data were included if the patients were 18 years or older, satisfied clinical criteria for pneumonia, and had both nasal swabbing and culturing of respiratory specimens within 24 hours of admission. A total of 165 patients met the inclusion criteria. Most had either community-acquired or health care-associated pneumonia. Of the 28 patients with a nasal swab positive for methicillin-resistant S aureus, 8 (4.8%) also had respiratory tract cultures positive for the microorganism. Among the 165 patients, 2 (1.2%) had negative nasal swabs but positive respiratory cultures. Sensitivity and specificity of nasal colonization with methicillin-resistant S aureus for subsequent infection with the pathogen were 80% and 87.1%, respectively; positive and negative predictive values were 28.6% and 98.5%, respectively. Nasal screening for methicillin-resistant S aureus may be a valuable tool for de-escalation of empiric therapy targeted to the organism, especially in patients admitted for severe community-acquired or health care-associated pneumonia. The high negative predictive value suggests that patients with a negative nasal swab most likely do not have a lower respiratory tract infection caused by the organism. ©2015 American Association of Critical-Care Nurses.American Journal of Critical Care 01/2015; 24(1):8-12. DOI:10.4037/ajcc2015102 · 1.60 Impact Factor
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ABSTRACT: Nasal decolonisation has a proven effect on the prevention of severe Staphylococcus aureus infections and in the control of methicillin resistant S. aureus (MRSA). However, rising rates of resistance to antibiotics highlights the need for new substances for nasal decolonisation. LTX-109 is a broad spectrum, fast-acting bactericidal antimicrobial drug for topical treatment, which causes membrane disruption and cell lysis. This mechanism of action is not associated with cross-resistance and has a low propensity for development of resistance. In the present study persistent nasal MRSA and methicillin sensitive S. aureus carriers were treated for three days with vehicle, 1%, 2% or 5% LTX-109, respectively. A significant effect on nasal decolonisation was observed already after 2 days of LTX-109 treatment in subjects treated with 2% or 5% LTX-109 compared to vehicle (P≤0.0012, Dunnett's test). No safety issues were noted during the 9-week follow-up period. Minimal reversible epithelial lesions were observed in the nasal cavity. The systemic exposure was very low with a Cmax 1-2 h post dosing (3.72-11.7 ng/mL). One week after treatment initiation LTX-109 was not detectable in any subject. Summary: Intranasal treatment of S. aureus with LTX-109 is safe and reduces the bacterial load already after a single day of treatment. Hence, LTX-109 has the potential as a new and effective antimicrobial agent with low propensity of resistance development that can prevent infections by MSSA/MRSA during hospitalization. ClinicalTrials.gov: NCT01158235.Antimicrobial Agents and Chemotherapy 10/2014; 59(1). DOI:10.1128/AAC.03513-14 · 4.45 Impact Factor