Lack of methicillin-resistant Staphylococcus aureus nasal carriage among patients at a primary-healthcare unit in Porto Alegre, Brazil

Ausência do carreamento nasal de Staphylococcus aureus resistentes à meticilina em pacientes em unidade básica de saúde de Porto Alegre, Brasil

MICROBIOLOGY

Lack of methicillin-resistant Staphylococcus aureus nasal carriage among patients at a primary-healthcare unit in Porto Alegre, Brazil

Ausência do carreamento nasal de Staphylococcus aureus resistentes à meticilina em pacientes em unidade básica de saúde de Porto Alegre, Brasil

Letícia Vale Scribel^I; Mariana Vale Scribel^II; Ernídio Bassani^III; Afonso Luis Barth^IV; Alexandre Prehn Zavascki^V

^IHospital da Aeronáutica de Canoas, Canoas, RS, Brazil

^IIMedical School, Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre, RS, Brazil

^IIIMedical School, Universidade Federal do Rio Grande do Sul, Brazil

^IVClinical Pathology Service, Hospital de Clínicas de Porto Alegre, Porto Alegre, RS, Brazil

^VInfectious Diseases Service, Hospital de Clínicas de Porto Alegre, 2350 Ramiro Barcelos St, 90035-903 Porto Alegre, RS, Brazil

^{Correspondence to}

SUMMARY

INTRODUCTION: Community-associated methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a pathogen in individuals without traditional risk factors.

MATERIAL AND METHODS: MRSA nasal carriage was assessed in individuals consulting at a Primary Health Unit in Brazil.

RESULTS: A total of 336 individuals were included: 136 were tested only for MRSA and 200 for any S. aureus. No MRSA was found among the 336 individuals and 23 (11.5%) of 200 were colonized by S. aureus.

DISCUSSION: Low prevalence rates have been found in non-hospitalized individuals, but MRSA surveillance should be encouraged to monitor clinical and molecular epidemiology of CA- MRSA.

Keywords: Prevalence; Nasal carriage; Methicillin-resistant Staphylococcus aureus.

RESUMO

INTRODUÇÃO:Staphylococcus aureus resistentes à meticilina associados à comunidade (CA-MRSA) têm emergido como patógeno em indivíduos sem os tradicionais fatores de risco.

MATERIAIS E MÉTODOS: Carreamento nasal de MRSA foi avaliado em indivíduos atendidos em unidade básica de saúde.

RESULTADOS: 336 indivíduos foram incluídos: 136 foram testados somente para MRSA e 200 para qualquer S. aureus. Nenhum MRSA foi encontrado nos 336 indivíduos e 23 (11.5%) de 200 eram colonizados por S. aureus.

DISCUSSÃO: Baixas taxas de prevalência têm sido encontradas em indivíduos não-hospitalizados, entretanto a vigilância de MRSA é encorajada para o monitoramento da epidemiologia clínica e molecular do CA- MRSA.

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen. In recent years, however, community-associated (CA)-MRSA has emerged as a pathogen in adults and children without traditional risk factors for MRSA acquisition³. These isolates have their mecA gene carried in staphylococcal chromosomal cassettes (SCCmec), usually types IV or V, which are distinct from those classically associated with healthcare-associated MRSA³. CA-MRSA isolates are also more often susceptible to non-beta-lactams antibiotics and more frequently carry the Panton-Valentine Leukocidin genes³.

The most common site for S. aureus carriage is the nose, and nasal carriage of CA-MRSA strains is associated with a higher incidence of clinical infection^9,10,12. Prevention of staphylococcal infections and reduction of the spread of CA-MRSA are of great importance¹². Thus, the objective of this report was to assess the prevalence of MRSA nasal carriage among individuals consulting at a primary-healthcare unit (PHU) in Porto Alegre, Brazil, where most cases of CA-MRSA from Brazil have been reported so far¹¹.

MATERIAL AND METHODS

Nares culture specimens were obtained from individuals attending Santa Cecília PHU, Porto Alegre, from March 2008 to December 2008. All consecutive individuals > 18 years, enrolled in randomly selected days, were included in the study. Individuals who were not resident in the Porto Alegre city or who were unable to answer the questionnaire were excluded. The individuals were interviewed after their consultation and the variables collected were those presented in Table 1.

The individuals had the distal part of their anterior nares sampled for culture with five circular movements of each side with a swab. The swabs were immediately processed at the Microbiology Laboratory of Hospital de Clínicas de Porto Alegre. In the first period of study, the swabs were plated onto Mannitol agar supplemented with 6 µg/mL oxacillin. Since no MRSA had been found when around one third of the expected sample size had been completed, the swabs were plated onto Mannitol agar without oxacillin. Isolates were identified by Vitek system (bioMérieux, Marcy l'Etoile, France) and free-coagulase test. Oxacillin susceptibility was determined by disk diffusion test as recommended by the Clinical and Laboratory Standards Institute².

The study was approved by the local ethics committee. All patients signed information consent. Statistical analyses were carried out at the SPSS for Windows vs 13.0. All tests were two-tailed and a p < 0.05 was considered significant.

RESULTS

A total of 336 individuals were included in the study. The first 136 were assessed only for MRSA since the nasal swabs were plated onto selective media. The remaining 200 individuals had their swabs plated onto non-selective media. Among all 336 subjects, no MRSA was identified. Among the group of 200 subjects, 23 (11.5%) had S. aureus recovered from their nares. There was no significantly different characteristic between individuals who had their nasal swab plated on selective media and those where the swabs were plated on non-selective media, except for diabetes, which was more frequently among the former ones (21.3% versus 10.5%, respectively, p = 0.01). No variable was found to be significantly associated with S. aureus nasal carriage (Table 1).

DISCUSSION

Our study found no MRSA nasal carriage among patients attended to a PHU from Porto Alegre, a Brazilian city where the first CA-MRSA has been described in South America and where most cases of CA-MRSA have been described so far¹¹. This result may be partially explained by the fact that we did not assess children, a population with higher rates of MRSA colonization¹³. Additionally, it should be acknowledged that nasal cultures may underestimate the real prevalence of S. aureus colonization, since it can also be found in other parts of the body as well, such as axilla and pharynx⁷. Our study had the capacity to detect a prevalence of 2 ± 2% with a 95% confidence interval. So, we were unable to detect a lower prevalence and it is possible that a prevalence lower than 2% could be undetected with our sample size.

MRSA have been considered a public health threat in Brazil¹, but, so far, no study has assessed the prevalence of CA-MRSA in the community in Brazil. Other community-based studies have also found low MRSA nasal carriage prevalence. HALABLAB et al.⁵ have found eight (1.6%) MRSA nasal carries among 500 studied subjects. LAMARO-CARDOSO et al.⁶ have assessed 1192 children and MRSA carriage was detected in 14 (1.2%) individuals. MONECKE et al.⁸ have found 1.94% of MRSA among 155 S. aureus isolates recovered from asymptomatic carriers in Saxony, Germany. MUNCKHOF et al.⁹ have found a prevalence of only 0.7% among 699 patients in Queensland, Australia.

GIULIANI et al. in a study conducted at Rome have also not found any MRSA in nasal swabs of HIV-1-infected men who have sex with men⁴. The authors have emphasized the importance of knowledge of local epidemiology concerning CA-MARSA prevalence, since their findings were, as was ours, very distinct from other regions, particularly from the United States, where higher rates have been found⁴.

In summary, we presented a surveillance study showing the absence of MRSA nasal carriage among low-risk individuals. No risk factor was found to be significantly associated with S. aureus nasal carriage. We believe that MRSA surveillance studies in the community setting should be encouraged to gain a better understanding of clinical and molecular epidemiology of the emerging CA-MRSA isolates.

ACKNOWLEDGEMENTS

This study was supported by Fundo de Incentivo à Pesquisa e Eventos - FIPE of Hospital de Clínicas de Porto Alegre, Brazil and Fundação de Amparo à Pesquisa do Rio Grande do Sul - FAPERGS. APZ receives research fellow from CNPq (301829/2008-0).

CONFLICT OF INTEREST

The authors declare that there is no conflict of interest.

Received: 12 January 2011

Accepted: 11 July 2011

• 1. Carvalho KS, Mamizuka EM, Gontijo Filho PP. Methicillin/Oxacillin-resistant Staphylococcus aureus as a hospital and public health threat in Brazil. Braz J Infect Dis. 2010;14:71-6.
• ²
  Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing: 17^th information supplement (M100-S17). Wayne, PA: Clinical and Laboratory Standards Institute; 2007.
• 3. Deleo FR, Otto M, Kreiswirth BN, Chambers HF. Community-associated meticillin-resistant Staphylococcus aureus. Lancet. 2010;375:1557-68.
• 4. Giuliani M, Longo B, Latini A, Prignano G, Monaco M, de Santis A, et al. No evidence of colonization with community-acquired methicillin-resistant Staphylococcus aureus in HIV-1-infected men who have sex with men. Epidemiol Infect. 2010;138:738-42.
• 5. Halablab MA, Hijazi SM, Fawzi MA, Araj GF. Staphylococcus aureus nasal carriage rate and associated risk factors in individuals in the community. Epidemiol Infect. 2010;138:702-6.
• 6. Lamaro-Cardoso J, de Lencastre H, Kipnis A, Pimenta FC, Oliveira LS, Oliveira RM, et al. Molecular epidemiology and risk factors for nasal carriage of Staphylococcus aureus and methicillin-resistant S. aureus in infants attending day care centers in Brazil. J Clin Microbiol. 2009;47:3991-7.
• 7. Lautenbach E, Nachamkin I, Hu B, Fishman NO, Tolomeo P, Prasad P, et al. Surveillance cultures for detection of methicillin-resistant Staphylococcus aureus: diagnostic yield of anatomic sites and comparison of provider- and patient-collected samples. Infect Control Hosp Epidemiol. 2009;30:380-2.
• 8. Monecke S, Luedicke C, Slickers P, Ehricht R. Molecular epidemiology of Staphylococcus aureus in asymptomatic carriers. Eur J Clin Microbiol Infect Dis. 2009;28:1159-65.
• 9. Munckhof WJ, Nimmo GR, Schooneveldt JM, Schlebusch S, Stephens AJ, Williams G, et al. Nasal carriage of Staphylococcus aureus, including community-associated methicillin-resistant strains, in Queensland adults. Clin Microbiol Infect. 2009;15:149-55.
• 10. Safdar N, Bradley EA. The risk of infection after nasal colonization with Staphylococcus aureus. Am J Med. 2008;121:310-5.
• 11. Scribel LV, Silva-Carvalho MC, Souza RR, Superti SV, Kvitko CH, Figueiredo AM, et al. Clinical and molecular epidemiology of methicillin-resistant Staphylococcus aureus carrying SCCmecIV in a university hospital in Porto Alegre, Brazil. Diagn Microbiol Infect Dis. 2009;65:457-61.
• 12. Sdougkos G, Chini V, Papanastasiou DA, Christodoulou G, Stamatakis E, Vris A, et al. Community-associated Staphylococcus aureus infections and nasal carriage among children: molecular microbial data and clinical characteristics. Clin Microbiol Infect. 2008;14: 995-1001.
• 13. Wertheim HF, Melles DC, Vos MC, van Leeuwen W, van Belkum A, Verbrugh HA, et al. The role of nasal carriage in Staphylococcus aureus infections. Lancet Infect Dis. 2005;5:751-62.

Publication Dates

• Publication in this collection
  05 Sept 2011
• Date of issue
  Aug 2011

History

• Received
  12 Jan 2011
• Accepted
  11 July 2011