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Nasal Carriage of Methicillin-Resistant Staphylococcus aureus in Household Contacts of Children With Community-Acquired Diseases in Taiwan

Huang, Yhu-Chering MD, PhD*†; Ho, Chen-Fang MD*; Chen, Chih-Jung MD*; Su, Lin-Hui MS†‡; Lin, Tzou-Yien MD*†

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The Pediatric Infectious Disease Journal: November 2007 - Volume 26 - Issue 11 - p 1066-1068
doi: 10.1097/INF.0b013e31813429e8
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Abstract

Recent reports indicate that community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are increasing and may now involve persons without risk factors predisposing for acquisition.1–3 In the United States, CA-MRSA strains have been recognized as a novel pathogen that is genetically different from the nosocomial MRSA.2 They are characterized by limited antibiotic resistance, share 2 common pulsed field gel electrophoresis (PFGE) patterns (USA 300 and USA 400), and contain type IV staphylococcal cassette chromosome (SCCmec).1–3 SCCmec is the genetic element that carries the methicillin-resistant gene, mecA, and there are at least 5 SCCmec types identified at present.

In Taiwan, epidemiologic data4–7 showed that between 1997 and 2003, MRSA accounted for 9.8-36% of community-acquired S. aureus infections in children without risk factors and MRSA colonization rate in the general population ranged from 1.9% in school children, 5.3% in healthy children presented for healthcare visits, to 10.8% in health care workers and 13.6% in contacts of CA-MRSA infection. To understand the transmission of CA-MRSA isolates in the households, we conducted an epidemiologic investigation to survey the nasal carriage of MRSA among the household contacts of children with CA-MRSA infection.

MATERIALS AND METHODS

Between August 2004 and May 2005, once a hospitalized patient with CA-MRSA infection, which was defined as an MRSA infection documented within 72 hours of admission, was identified at Chang Gung Children's Hospital, an investigator (C.-F.H.) would interview the care provider of the patients to complete a questionnaire about hospitalization, surgery, dialysis, a permanent indwelling catheter or percutaneous medical device, a known positive culture for MRSA before this infection, and history of residence in a long-term care facility within the previous 12 months. Patients with any of these conditions were defined as having an identifiable risk factor.2 Those <1 year of age were defined as without identifiable risk factor if they do not have any condition after birth, except birth in the hospital. After a written consent was obtained from the guardians and/or the case patients, a survey culture of the anterior nares was obtained from the case patients and their household contacts within 1 week of when the MRSA was identified.

Identification of MRSA was confirmed according to Clinical and Laboratory Standards Institute guidelines, 2005. PFGE with SmaI digestion was performed as described previously.5,8 Two isolates were considered to be indistinguishable, highly related, or distinct if the bands were identical, fewer than 4-band differences, or 4 or more bands differences.

SCCmec typing was determined by a multiplex polymerase chain reaction strategy described previously.9 SCCmec typing for type VT was modified from Boyle-Vavra et al.7 The presence of Panton-Valentine leukocidin (PVL) genes was determined by a polymerase chain reaction strategy described previously.10 All clinical isolates underwent multilocus sequence typing as described elsewhere.11

RESULTS

During the study period, 109 children <18 years of age with CA-MRSA infections were identified. The household members of 57 children were available and willing to come to the hospital for sampling and included in this study. Of the 57 case patients, 49 patients (86%) presented with simple skin and/or soft tissue infection. Identifiable risk factor for MRSA acquisition was identified in 12 (21%) children.

Of the 57 families included, a total of 121 household contacts were sampled. There was 1 member sampled in 17 households, 2 members in 27 households, and 3 or more members in 13 households. MRSA was detected in 30 contacts (25%) from 23 families (40%). Six households had 2 or more contacts positive for MRSA. Grandparents (35%) and mothers (33%) had the highest frequency of MRSA carriage (Table 1). Among the 57 case patients, nasal carriage of MRSA was detected in 18 case patients (32%). Two other case patients had MSSA colonization.

TABLE 1
TABLE 1:
Distribution of 121 Household Members From 57 Families Sampled for Nasal Carriage of Methicillin-Resistant Staphylococcus aureus (MRSA)

Seven PFGE patterns were identified. PFGE patterns D (accounting for 71% and 49% of the clinical and colonized isolates, respectively) and C (accounting for 15% and 32% of the clinical and colonized isolates, respectively) were the 2 most common patterns. SCCmec VT was the predominant type (67% of the clinical isolates and 47% of the colonized isolates), followed by type IV (27% of the clinical isolates and 45% of the colonized isolates). PVL genes were detected in 77% of the clinical isolates and in 55% of the colonization isolates. From the 48 clinical isolates, 7 sequence types (STs) were identified by multilocus sequence typing and ST59 was the most common ST, accounting for 79%. Altogether, ST59/PFGE type D/SCCmec VT/presence of PVL genes identified in 30 (67%) clinical isolates and ST59/PFGE type C/SCCmec IV/absence of PVL genes in 7 (15%) clinical isolates were the 2 most common clones.

Among the 16 paired clinical-colonization isolates available for clonal comparison from the case patients, 15 pairs (94%) were considered to be indistinguishable (also the same SCCmec types, STs, and PVL genes). Whereas, among the 28 paired isolates from the households, 18 pairs (64%), 5 pairs (18%), and 5 pairs were considered to be indistinguishable, highly related and distinct, respectively.

DISCUSSION

Results from this study indicate that nasal carriage of MRSA was detected in about one-third of the case patients and more than 90% of the colonization isolates were indistinguishable from the clinical isolates, suggesting that colonization of MRSA may be associated with subsequent infection.

Nasal carriage of MRSA was also detected in one-fourth of the household contacts surveyed. This rate was significantly higher than that in children without designated risk factors for the acquisition of MRSA in Taiwan (1.9–5.3%).4,7 Approximately two-thirds of the colonization isolates from household contacts were indistinguishable from the clinical isolates, indicating that MRSA can indeed spread in the household once MRSA emerges in a household member. However, distinct clones were identified in one-third of the isolates from household contacts, suggesting that not all MRSA isolates from the contacts were related to the case patient.

In this prospective study, we also found that there was a predominant clone of MRSA characterized by ST59, PFGE pattern D (similar to PFT USA 100012), SCCmec VT, and presence of PVL gene among the CA-MRSA isolates in Taiwanese children and this clone accounted for two-thirds of the clinical isolates. These findings are consistent with those reported previously from Taiwan,7,12 suggesting that this clone has been circulating in the Taiwan community.

REFERENCES

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Keywords:

community-acquired; methicillin-resistant Staphylococcus aureus; household; Taiwan

© 2007 Lippincott Williams & Wilkins, Inc.