Methicillin-resistant Staphylococcus aureus (MRSA) infections are a major public health problem. Active carrier detection is recommended among healthcare staff when there are nosocomial outbreaks or in highly endemic situations in certain risk areas.1 As future healthcare professionals, medical students must be aware of their role as potential sources of S. aureus transmission to patients. Our study had the following objectives: (a) to determine the carrier rate (nasal and/or pharyngeal) of methicillin-sensitive S. aureus (MSSA) and MRSA among third-year medical students at Universidad Complutense de Madrid, in Madrid, Spain, who had not yet started their practical placements at Hospital Clínico San Carlos; and (b) analyse possible risk factors.
Over six consecutive academic years (from 2014 to 2022), all students voluntarily had a pharyngeal and nasal sample taken, except in the 2021/2022 academic year when, due to the SARS-CoV-2 prevention and safety measures, the student's themselves took a nasal sample only. Inoculation was immediately carried out in two culture media for the isolation and identification of S. aureus: chromID SAID agar (bioMérieux S. aureus); and chromID MRSA agar (bioMérieux S. aureus). The students also anonymously completed a questionnaire assessing possible factors associated with a carrier state, such as gender, chronic sinusitis, acute sinusitis, taking antibiotics in the 10 days prior to the sample, hospital admissions or interventions and related local surgery. Chronic sinusitis was defined as inflammation of the sinuses with signs and symptoms lasting for at least 12 weeks.
The statistical analysis of the results was carried out with the Epi Info 7.2.5.0 program, considering a statistically significant result if p<0.05.
Of 607 students included, 369 (60.8%) were colonized by S. aureus, nine of them (1.5%) being carriers of MRSA. This overall colonization rate groups all types (nasal, pharyngeal and both), which is why it is so high compared to other studies that only take into account the culture of a nasal sample to assess S. aureus carrier status.2–5 However, it has been reported that if the pharyngeal culture is added to the nasal culture, detection sensitivity can be increased by 25.7%.6
The prevalence of MRSA found in the general population and pre-clinical students is in the range of 0.8%–1.8%.7,8 We obtained an MRSA colonization rate of 1.5%, within these margins.
Fig. 1 shows the distribution of colonized students according to the academic year and the location (nasal, pharyngeal or both). A total of 250 students (41.2%) were colonized at least in the nose, this rate being higher than that described in some university students in our area.2,3 However, other studies carried out in pre-clinical students report colonization rates of 40.8%4 and 43.6%.5 Where S. aureus colonizes the nose, with only a few exceptions, the bacterium is also present in the pharynx.9 In our study, 77.52% (169/218) of the students with nasal isolation of S. aureus were also colonized in the pharynx, and this association was statistically significant (p<0.001).
Although the primary S. aureus colonization site is the nostrils, some studies have isolated S. aureus more frequently from the pharynx than from the nose.9 Our results show that exclusively pharyngeal colonization was always more common than exclusively nasal colonization (22.53% vs 9.3%, p<0.001).
With regard to S. aureus carrier status, people with chronic sinusitis have been found to be at greater risk of being carriers.10 We found statistically significant differences between students colonized and non-colonized with S. aureus in the nose regarding chronic sinusitis (19.2% vs 8.4%, p<0.001). These data are consistent with the results from a previous study we conducted in 2008 on pre-clinical students from the same hospital.2
In short, our study shows a high rate of S. aureus colonization among third-year medical students, future healthcare professionals, with exclusively pharyngeal colonization being more common than that in the nose.
FundingNone.
Conflicts of interestNone.
