title: Nasal carriers are more likely to acquire exogenous Staphylococcus aureus strains than non-carriers.
abstract: We performed a prospective observational study in a clinical setting to test the hypothesis that prior colonization by a Staphylococcus aureus strain would protect, by colonization interference or other processes, against de novo colonization and, hence, possible endo-infections by newly acquired S. aureus strains. Three hundred and six patients hospitalized for >7 days were enrolled. For every patient, four nasal swabs (days 1, 3, 5, and 7) were taken, and patients were identified as carriers when a positive nasal culture for S. aureus was obtained on day 1 of hospitalization. For all patients who acquired methicillin-resistant S. aureus (MRSA) or methicillin-susceptible S. aureus via colonization and/or infection during hospitalization, strains were collected. We note that our study may suffer from false-negative cultures, local problems with infection control and hospital hygiene, or staphylococcal carriage at alternative anatomical sites. Among all patients, 22% were prior carriers of S. aureus, including 1.9% whom carried MRSA upon admission. The overall nasal staphylococcal carriage rate among dermatology patients was significantly higher than that among neurosurgery patients (n = 25 (55.5%) vs. n = 42 (16.1%), p 0.005). This conclusion held when the carriage definition included individuals who were nasal culture positive on day 1 and day 3 of hospitalization (p 0.0001). All MRSA carriers were dermatology patients. There was significantly less S. aureus acquisition among non-carriers than among carriers during hospitalization (p 0.005). The mean number of days spent in the hospital before experiencing MRSA acquisition in nasal carriers was 5.1, which was significantly lower than the score among non-carriers (22 days, p 0.012). In conclusion, we found that nasal carriage of S. aureus predisposes to rather than protects against staphylococcal acquisition in the nose, thereby refuting our null hypothesis.
authors.affiliation: Department of Medical Microbiology and Parasitology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Selangor, Malaysia; Faculty of Medicine, North Khorasan University of Medical Sciences, Bojnurd, Iran.
authors.forename: H
authors.initials: H
authors.lastname: Ghasemzadeh-Moghaddam
authors.affiliation: Department of Medical Microbiology and Parasitology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Selangor, Malaysia. Electronic address: neela2000@hotmail.com.
authors.forename: V
authors.initials: V
authors.lastname: Neela
authors.affiliation: Department of Medical Microbiology and Infectious Diseases, Erasmus MC, Rotterdam, The Netherlands.
authors.forename: W
authors.initials: W
authors.lastname: van Wamel
authors.affiliation: Department of Medical Microbiology and Parasitology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Selangor, Malaysia.
authors.forename: R A
authors.initials: RA
authors.lastname: Hamat
authors.affiliation: Department of Medical Microbiology and Parasitology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Selangor, Malaysia; Marine Science Laboratory, Institute of Bioscience, Universiti Putra Malaysia, Serdang, Malaysia.
authors.forename: M Nor
authors.initials: MN
authors.lastname: Shamsudin
authors.affiliation: Pathology Laboratories, Hospital Kuala Lumpur, Kuala Lumpur, Malaysia.
authors.forename: N Suhaila Che
authors.initials: NS
authors.lastname: Hussin
authors.affiliation: Pathology Laboratories, Hospital Kuala Lumpur, Kuala Lumpur, Malaysia.
authors.forename: M N
authors.initials: MN
authors.lastname: Aziz
authors.affiliation: Department of Neurosurgery, Hospital Kuala Lumpur, Kuala Lumpur, Malaysia.
authors.forename: M S Mohammad
authors.initials: MS
authors.lastname: Haspani
authors.affiliation: Department of Dermatology, Hospital Kuala Lumpur, Kuala Lumpur, Malaysia.
authors.forename: A
authors.initials: A
authors.lastname: Johar
authors.affiliation: Department of Dermatology, Hospital Kuala Lumpur, Kuala Lumpur, Malaysia.
authors.forename: S
authors.initials: S
authors.lastname: Thevarajah
authors.affiliation: Department of Medical Microbiology and Infectious Diseases, Erasmus MC, Rotterdam, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Vos
authors.affiliation: Department of Medical Microbiology and Infectious Diseases, Erasmus MC, Rotterdam, The Netherlands; bioMérieux, R&D Microbiology, La Balme les Grottes, France.
authors.forename: A
authors.initials: A
authors.lastname: van Belkum
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002353:Carrier State / Q000453:epidemiology* / Q000382:microbiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009297:Nasal Mucosa / Q000382:microbiology*; D015995:Prevalence; D011446:Prospective Studies; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000145:classification* / Q000302:isolation & purification*; D055815:Young Adult
keywords: Colonization; MRSA; Staphylococcus aureus; colonization interference; nasal carriage