Staphylococcus aureus in Your Nose Is it Safe to Carry It?
Abstract & Commentary
By Alan D Tice, MD, Infectious Disease Consultant, John A. Burns School of Medicine, University of Hawaii, Honolulu, Section Editor, Managed Care, is Associate Editor for Infectious Disease Alert.
Dr. Tice reports no financial relationships relevant to this field of study.
Synopsis: Learn to live with and accept the staphylococci in your nose.
Source: Sakwinska O, et al. Ecological temporal stability of Staphylococcus aureus nasal carriage. J Clin Microbiol. 2010;48:2724-2728.
Investigators in lausanne, switzerland cultured the noses of 405 new hospital workers for Staphylococcus aureus, then checked them again about nine months later. They characterized the isolates with spa typing, AFLP (amplified fragment length polymorphism), and DLST (double-length sequence typing).
The percentages of employees colonized at both samplings were remarkably similar, at 32% and 34% before and after employment. Of those colonized initially, only two had more than one strain, despite rigorous detection methods. Three strains were resistant to methicillin.
Of the 89 hospital workers colonized with S. aureus initially, 30% (27) lost it and it was not replaced. Of those not colonized initially, 34% (30) acquired a strain. The only variable found to correlate with losing the organism was a low colony count. No significant correlations were found with becoming colonized.
Of the 62 with persistent staphylococci, five workers acquired a new strain. It also was noted that there were mutations in spa typing in five of 53 strains that remained stable by the other methodology.
Commentary
The percentage of apparently normal people carrying staph infection in their nose is quite similar to that reported with the NHANES study in the United States.
It is apparent from this and prior research that some S. aureus strains will persist in an apparently innocuous state for long periods of time, if not for life. This suggests some people are an ideal match of host susceptibility and microbe. Measures to eradicate the organism from the nose may work temporarily, but prior studies suggest the same strain may return when the opportunity again arises. Whether there is any benefit to the host in this relationship is unclear, but there presumably is to the staphylococci. It also suggests the colonizing strain has a unique advantage over the innumerable other S. aureus strains that people are constantly exposed to and that it somehow has a monopoly of the region in the nose for some unknown reason.
It also is interesting that employment in the hospital did not affect the carriage rate and that it did not correlate with duration of employment in that health care environment.
The fact that mutations apparently occur in the same strain by spa analysis also is of note in that it suggests these may not be entirely dormant organisms and that they can learn or acquire new methods of virulence, antibiotic resistance, and spread without simply being replaced.
This study adds another small element to the research needed to answer the still elusive questions of how and why people are colonized with staphylococci, what triggers colonization to lead to infection (when it occasionally does), how virulence is acquired, and how these organisms spread.
With this added insight, it is clear that almost all nasal staphylococci are not the virulent and malevolent creatures some put them up to be even if they are MRSA. It may well be that the convenient, if not legitimate relationship between a host and these camp followers may be peaceful, and that disrupting this relationship may not be successful in the long run, may have unanticipated consequences, and could be counter-productive in the efforts to stave off the production of even more effective resistance mechanisms and survival factors that this wily organism is known for.
We need to better understand the host immunity factors and the specific virulence and spreading factors that lead to colonization and infection. This is now particularly true of the community-associated strains of staphylococci that colonize and likely infect more people in the community than are hospitalized.
References
- Van den Bergh MFQ, Yzerman EPF Follow-up of S. aureus nasal carriage after 8 years: Redefining the persistent carrier state J Clin Microbiol. 1999;37:3133-3140.
- Gorwitz RJ, Kruszman et al. Changes in the prevalence and nasal colonization. J Infect Dis. 2008;197:1226-1234.
- Tenover FC, McAlliser S. Characterization of S. aureus isolated from nasal cultures collected from individuals etc. JCM. 2008;46:2837-2841.
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