The first 3 months

May 2012


Staphylococcus aureus

A cross sectional study of prevalence and risk factors in one general practice

Volume 41, No.5, May 2012 Pages 325-328

Rebecca Warren


Infection control and antibiotic resistant organisms are a community health concern. This article presents findings of a cross sectional study of 100 users of the Thirroul Medical Practice clinical treatment room, in Thirroul, New South Wales.


Nasal Staphylococcus aureus colonisation rates and risk factors were investigated.


Twenty-six percent of participants (n=26) were found to have S. aureus; 11.5% (n=3) of cases were community acquired methicillin resistant S. aureus. Methicillin resistant S. aureus was significantly correlated with older age (p=0.02) and skin infection within the preceding year (p=0.03). Clinical staff (n=15) had low rates of S. aureus at 6.6% (n=1) and no methicillin resistant S. aureus.


Overall, S. aureus rates were unremarkable, but methicillin resistant S. aureus rates were higher than elsewhere with older patients most at risk. General practice staff developing infection control strategies should consider the vulnerable nature and cross-contamination risks in this group of patients. Encouragingly, clinical staff showed low levels of S. aureus and no methicillin resistant S. aureus.

Infection control and antibiotic resistant organisms are a community health concern. Research has focused on acute and high dependency facilities,1,2 but with care of chronically ill patients increasingly taking place in the community, these patients may be more susceptible to persistent bacterial colonisation and invasive infection. Staphylococcus aureus (SA), particularly community acquired methicillin resistant Staphylococcus aureus (MRSA) is increasingly virulent and invasive.2

Staff at the Thirroul Medical Practice (TMP), in Thirroul, New South Wales, have long committed to minimising cross-contamination within the practice. This article presents a cross sectional study aimed at measuring the point prevalence of nasal SA colonisation in users of the TMP clinical treatment room and identifying associated risk factors.


Recruitment and data collection occurred between 24 January and 4 February 2011. People aged over 18 years entering the TMP treatment room during this period were eligible to participate. Two refused, both tending to acutely unwell children; however 100 participants formally consented to involvement. All 15 eligible TMP clinical staff were recruited. Remaining participants included nonclinical staff, patients, carers and family members.

Data collection

Participants’ nares were swabbed for microbiological examination. Participants were identified as clinical staff or ‘other’ and verbally surveyed to gather information about age, gender and potential risk factors including if the person:

  • entered the treatment room to manage a chronic wound
  • was immune suppressed
  • had been admitted to a nursing home or hospital within the past 12 months
  • had worked as a clinical team member in a hospital or nursing home within the past 12 months
  • experienced a skin infection within the past 12 months.

Microbiological processing

Microbiological samples were collected using Transwabs®. At the laboratory, samples were cultured onto blood agar plates and incubated overnight in carbon dioxide maintained at 35°C. Results were confirmed by DNase and staphylococcus agglutination latex testing and submitted to antibiotic calibrated dichotomous sensitivity testing.


Statistical analyses were conducted using VasserStats calculators.3 Point prevalence of colonisation was established. Data was analysed using a calculated correlation matrix and tested using Fisher’s exact probability testing. Twotailed p values, calculated odds ratios and 95% confidence intervals are reported. Some analyses utilise descriptive statistics where results of interest arise from small subgroups.

Samples were processed at no cost by Southern IML pathology, who had no further involvement and did not seek or receive resulting data. The study was conducted in accordance with the requirements of the Human Research Ethics Committee of the University of Wollongong and the approval number was HE09/244/10/042.

Table 1. Demographic and other survey response data (% = n)
Male 33 Female 67
Age <70 years 32 Age 70+ years 68
TMP team member 15 TMP team member 85
Chronic wound 31 Chronic wound 69
Immune compromised 21 Immune compromised 79
Hospital stay 27 Hospital stay 73
Hospital team 10 Hospital team 90
Infection 29 Infection 71


Staphylococcus aureus colonisation was found in 26% (n=26) of participants. Methicillin resistant SA was identified in 3% (n=3) which represents 11.5% of SA. Survey responses are shown in Table 1. The prevalence of SA was analysed against the surveyed factors (Table 2). Two groups demonstrated statistically significant correlation with SA: participants aged over 70 years (p=0.02) and participants reporting skin infection within the preceding year (p=0.04). The prevalence of SA in clinical team members was 6.6% (n=1) and nonteam members 29.4% (n=25) (p=0.1). There was no MRSA among team members. Three MRSA colonies were identified; each strain community acquired and all in participants aged over 70 years. The number affected (n=3) is small but represents:

  • 9.3% of participants aged over 70 years (n=32, p=0.03)
  • 23% (n=3) of the SA colonised of participants aged over 70 years (n=13) (Table 3).

It was observed that of MRSA colonised participants, two were female and had none of the other risk factors considered in the study.

Table 2. Calculated correlations between prevalence of nasal SA colonisation and other surveyed factors
(% = n)
NSA +ve
NSA –veORCIp value
% (n) % (n)
Factors which were current
Total 100 26 (26) 74 (74)      
Male 33 36.3 (12) 63.7 (21) 0.4 0.1–1.1 0.14
Female 67 20.8 (14) 79.2 (53)      
Age 18–69 years 68 19.1 (13) 80.9 (55) 0.3 0.1–0.8 0.02*
Age 70+ years 32 40.6 (13) 59.4 (19)      
TMP team Y 15 6.6 (1) 93.4 (14) 5.8 0.7–46 0.1
TMP team N 85 29.4 (25) 70.6 (60)      
Chronic wound Y 31 35.4 (11) 64.6 (20) 0.5 0.1–1.2 0.21
Chronic wound N 69 21.7 (15) 78.3 (54)      
Immune comp Y 21 23.8 (5) 76.2 (16) 1.1 0.3–3.5 1
Immune comp N 79 29.6 (21) 70.4 (58)      
Factors relating to exposure over previous 12 months
Hospital stay Y 27 33.3 (9) 66.7 (18) 0.6 0.2–1.5 0.31
Hospital stay N 73 23.2 (17) 76.8 (56)      
Hospital team Y 10 10 (1) 90 (9) 3.4 0.4–28.7 0.44
Hospital team N 90 27.7 (25) 72.3 (65)      
Infection Y 29 41.3 (12) 58.7 (17) 0.3 0.1–0.8 0.04*
Infection N 71 19.7 (14) 80.3 (57)      
* p value of <0.05 was considered significant; OR = odds ratio; CI = confidence interval; NSA = nasal S. aureus; Y = yes; N = no


This small study demonstrates a substantially different MRSA prevalence from those identified elsewhere1,2,4 including:

  • The Netherlands, where nasal swabs of 2691 general practice patients identified 23% prevalence of SA and no MRSA5
  • the United States, where a large population based study found around 30% SA prevalence and 0.84% MRSA6
  • Queensland, where a study of 699 adults – 396 patients of a specified practice and 303 others from the community – found SA in 28.9% (n=202) and 0.3% (n=2) MRSA.7

Staphylococcus aureus within the TMP group is unremarkable at 26%, however, MRSA rates vary across groups but at 3% were much higher at the TMP group than other community studies.

Table 3. Calculated correlations between prevalence of nasal SA and MRSA colonisation and age
DemographicsTotal % = nMRSA +ve % (n)MRSA –ve % (n)p value
Total 100 3 (3) 97 (97)  
Age 18–69 years 68 0 (0) 100 (68) 0.03
Age 70+ years 32 9.3 (3) 90.7 (29)  
Total number SA +ve 26 11.5 (3) 88.5 (23)  
Age 18–69 years and SA +ve 13 0 (0) 100 (13) 0.22
Age 70+ years and SA +ve 13 23 (3) 77 (10)  
* Note: OR and CI for these analyses were unable to be completed. A complete table of calculated correlations between incidence of nasal SA and MRSA colonisation and all other studied factors is available from the author on request

Older age

Older age significantly correlated with SA (p=0.02) and MRSA (p=0.03) in study participants. This is generally consistent with other research;1,6 although Munckhof7 found no significant relationship. Rates of MRSA in older TMP participants 9.3% (n=3) are high compared to a study of 962 older Nottingham (United Kingdom) health district residents8 where MRSA was identified in just 0.83% (n=8). Nottingham participants were aged over 65 years, while older TMP participants were defined as aged over 70 years. Given that, and the small TMP sample size, the reason for the high prevalence in TMP participants is uncertain. Antibiotic use has been linked to MRSA carriage6,9 and older participants may have increased lifetime exposure to antibiotics but differences in prescribing between study regions are not known.

Skin infections

History of skin infection was significantly correlated to current SA (p=0.04). Other researchers’ findings vary widely;10 Munckhof7 and Miller11 found no significant relationships between SA and recent skin infection while other researchers have linked these factors.12

Clinical staff

Clinical staff comprised 15 participants, with one case of SA (6.6%) and no cases of MRSA. In comparison, nasal swabs from 78 Irish general practitioners identified MRSA in 7.9% (n=8) (SA was unreported).13 Wider study of community healthcare workers (HCWs) is lacking; however one literature review describes screening of more than 33 000 hospital HCWs and reports 23.7% SA and 4.1% MRSA cases.10 The lower TMP figures do not support statistically significant conclusions but may initiate discussion and further research.

Thirroul Medical Practice team members have long been committed to staff hand-wash protocols and practices aimed to involve patients – such as the provision of patient hand-wash and masks for those with respiratory symptoms. The possibility that, with these or other measures, TMP staff might have achieved significantly low rates of SA and MRSA carriage is an exciting one. Larger scale research into the prevalence of SA and MRSA among community healthcare providers may help clarify, particularly of correlation between HCW prevalence and local risk reduction measures. Longitudinal follow up would enable the assessment of carrier status as it is estimated that roughly 40% of colonisation will be persistent and 60% transient.17

Risk management strategies

The study findings have important consequences for infection control planning in general practices. Broad concern exists about the risk of transmission from HCWs to patients12 or HCWs’ family members.14 Hospitals in New South Wales have been consistently found to have among the highest rates of MRSA in Australia.15 In response strict hand washing and other policies aimed at reducing cross contamination between patients and HCWs have been introduced.16 There is also an increasing need to address these issues within primary care.

Methicillin resistant S. aureus colonisation may be the single most important factor determining invasive infection risk.17,18

Additional infection control methods may be warranted for TMP patients, particularly the vulnerable elderly. Decolonisation strategies are out of favour19,20 as colonies frequently re-form and display increased resistance.21,22 Hand washing is somewhat effective in reducing cross-contamination.23 The extension of handwash protocols to all patients and visitors may reduce cross-contamination within community practice. Use of gloves by patients or staff with known risk factors – such as skin infections, paronychia24 or artificial nails25 – is worthy of consideration. Best results are likely where practices actively promote strategic patient collaboration and engagement.9


Participants at TMP had SA rates comparable to other prevalence studies, but higher than expected MRSA. Older patients appear most at risk of colonisation and invasive disease.17 Infection control strategies should reflect the vulnerable nature and cross-contamination risk posed by this group. Staff at TMP had remarkably low levels of SA and no MRSA, an encouraging preliminary result that warrants further research.

Implications for general Practice

  • Community MRSA colonisation rates vary and are different to rates in acute care.
  • Older patients may be most at risk.
  • Long term commitment to risk reduction strategies may contribute to reduced colonisation in practice staff.


This research was completed during a year-long regional general practice placement undertaken as part of the MBBS program at the University of Wollongong, NSW. The author would like to thank the Thirroul Medical Practice community and particularly Dr Ann Ellacott for facilitating and supporting this placement, as well as Southern IML pathology for microbiological processing.


  1. Turnidge JD, Kotsanas D, Munckhof W, et al. Staphylococcus aureus bacteraemia: a major cause of mortality in Australia and New Zealand. Med J Aust 2009;191:368–73.
  2. Vlack S, Cox L, Peleg AY, et al. Carriage of methicillin-resistant Staphylococcus aureus in a Queensland Indigenous community. Med J Aust 2006;184:556–9.
  3. Lowry R. VassarStats website for statistical computation. Available at [Accessed 18 February 2011].
  4. Eveillard M, de Lassence A, Lancien E, Barnaud G, Ricard J, Joly–Guillou M. Evaluation of a strategy of screening multiple anatomical sites for methicillin-resistant Staphylococcus aureus at admission to a teaching hospital. Infect Control Hosp Epidemiol 2006;27:181–4.
  5. Donker GA, Deurenberg RH, Driessen C, Sebastian S, Nijs S, Stobberingh EE. The population structure of Staphylococcus aureus among general practice patients from The Netherlands. Clin Microbiol Infect 2009;15:137–43.
  6. Mainous AG, Hueston WJ, Everett CJ, Diaz VA. Nasal carriage of Staphylococcus aureus and methicillin-resistant S. aureus in the United States, 2001–2002. Ann Fam Med 2006;4:132–7.
  7. Munckhof WJ, Nimmo GR, Schooneveldt JM, et al. Nasal carriage of Staphylococcus aureus, including community-associated methicillinresistant strains, in Queensland adults. Clin Microbiol Infect 2009;15:149–55.
  8. Grundmann H, Tami A, Hori S, Halwani M, Slack R. Nottingham Staphylococcus aureus population study: prevalence of MRSA among elderly people in the community. BMJ 2002; 324:1365–6.
  9. Davey P, Pagliari C, Hayes A. The patient’s role in the spread and control of bacterial resistance to antibiotics. Clin Microbiol Infect 2002;8:43–68.
  10. Wolf J, Daley AJ, Tilse MH, et al. Antibiotic susceptibility patterns of Staphylococcus aureus isolates from Australian children. J Paediatr Child Health 2010;46:404–11.
  11. Miller M, Cook HA, Furuya EY, Bhat M, Lee M–H. Staphylococcus aureus in the community: colonization versus infection. PLoS One 2009;4:e6708.
  12. Albrich W and Harbath S. Health-care workers: source, vector, or victim of MRSA? Lancet Infect Dis 2008;8:289–301.
  13. Mulqueen J, Cafferty F, Cormican M, Keane J, Rossne A. Nasal carriage of methicillin-resistant Staphylococcus aureus in GPs in the west of Ireland. Br J Gen Pract 2007;57:811–3.
  14. Eveillard M, Martin Y, Hidri N, Boussougant Y, Joly-Guillou ML. Carriage of methicillin-resistant Staphylococcus aureus among hospital employees: prevalence, duration, and transmission to households. Infect Control Hosp Epidemiol 2004;25:114–20.
  15. AGAR Group. Staphylococcus aureus Survey 2007. Antimicrobial susceptibility report. Available at SAP07%20Report%20Final.pdf [Accessed 27 February 2011].
  16. Health Department NSW. Methicillin resistant Staphylococcus aureus (MRSA) in the community: response protocol for NSW public health units. Available at guideline/methicillin_res_stap.html [Accessed 31 October 2011].
  17. VandenBergh MF, Yzerman EP, van Belkum A, Boelens HA, Sijmons M, Verbrugh H. Follow-up of Staphylococcus aureus nasal carriage after 8 years: redefining the persistent carrier state. J Clin Microbiol 1999;37:3133–40.
  18. Henderson DK. Managing methicillin-resistant staphylococci: a paradigm for preventing nosocomial transmission of resistant organisms. Am J Infect Control 2006;34(5 Suppl 1):S46–54: discussion S64–73.
  19. Harbarth S, Fankhauser C, Schrenzel J, et al. Universal screening for methicillin-resistant Staphylococcus aureus at hospital admission and nosocomial infection in surgical patients. JAMA 2008;299:1149–57.
  20. Lee BY, Bailey RR, Smith KJ, et al. Universal methicillin-resistant Staphylococcus aureus (MRSA) surveillance for adults at hospital admission: an economic model and analysis. Infect Control Hosp Epidemiol 2010;31:598–606.
  21. Muto C. Methicillin-resistant Staphylococcus aureus control: We didn’t start the fire, but it’s time to put it out. Infect Control Hosp Epidemiol 2006;27:111–5.
  22. Turnidge J. Multiresistant organisms at the front line. Australian Prescriber 2010;33:68–71.
  23. McLaws M-L, Pantle AC, Fitzpatrick KR, Hughes CF. More than hand hygiene is needed to affect methicillin-resistant Staphylococcus aureus clinical indicator rates: clean hands save lives, Part IV. Med J Aust 2009;191:S26–31.
  24. Health Department of NSW. Resource packages: methicillin resistant Staphylococcal aureus (MRSA). Available at /infection/resource%20packages/mrsa.asp [Accessed 31 October 2011].
  25. Boyce J. Patient information: methicillin- resistant Staphylococcus aureus. Available at– information–methicillin–resistant– staphylococcus–aureus–mrsa [Accessed 31 October


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