Pediatric Surgery International

, Volume 22, Issue 8, pp 683–687

A high prevalence of methicillin-resistant Staphylococcus aureus among surgically drained soft-tissue infections in pediatric patients

Authors

  • John Seal
    • University of Chicago Pritzker School of Medicine
    • Division of Pediatric Surgery, Department of SurgeryUniversity of Chicago
  • Mindy Statter
    • Division of Pediatric Surgery, Department of SurgeryUniversity of Chicago
  • Donald Liu
    • Division of Pediatric Surgery, Department of SurgeryUniversity of Chicago
Original Article

DOI: 10.1007/s00383-006-1684-x

Cite this article as:
Seal, J., Glynn, L., Statter, M. et al. Pediatr Surg Int (2006) 22: 683. doi:10.1007/s00383-006-1684-x

Abstract

Over the past decade, methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a global problem, prompting extensive surveillance efforts. A previous study of S. aureus isolates at our institution revealed alarming increases in the prevalence of MRSA with no sign of plateau. However, evidence of MRSA in pediatric surgical patients remains largely anecdotal, as there are no published reports of institutional MRSA surveillance in the pediatric surgical literature. We conducted a retrospective review of incision and drainage (I and D) procedures at our institution from 1998 through 2004. All I and D procedures performed at the University of Chicago Children’s Hospital were identified and the patients’ charts reviewed for pertinent information. A total of 99 I and D procedures were performed during the study period, ranging from 5 in 1998 to 32 in 2004. Among cultures with positive growth, 52 (65.8%) were MRSA, 14 (17.7%) were methicillin-sensitive S. aureus, and 13 (16.5%) were miscellaneous species. The number of MRSA isolates increases from 2 in 1998 to 20 in 2004, the largest increase occurring during the last 3 years of the study. A large proportion of MRSA isolates were resistant to antimicrobials from other classes, with over 70% being resistant to both erythromycin and cefazolin. A majority of MRSA isolates (71.4%) were obtained from patients with no record of prior hospitalization. Our analysis confirms a high prevalence of MRSA among soft-tissue infections requiring surgical drainage. In addition, a majority of MRSA isolates were resistant to multiple antimicrobials and were isolated from children without a previous documented exposure to the hospital milieu. Thus, pediatric surgeons should be aware of MRSA prevalence and resistance patterns in the local communities.

Keywords

MRSAAbscessAntimicrobial resistanceStaphylococcus aureus

Introduction

Staphylococcus aureus is a ubiquitous pathogen responsible for sporadic infections and epidemics worldwide. Over the past decade, methicillin-resistant S. aureus (MRSA) has emerged as a global problem, prompting extensive surveillance efforts [16]. Within our community, MRSA has emerged as a serious clinical problem. A previous study of S. aureus isolates at our institution revealed an alarming increase in the prevalence of MRSA with no sign of plateau [7].

In addition to an increase in prevalence, important changes in the epidemiology of MRSA have recently been reported. Although once considered to be primarily a nosocomial pathogen prevalent only among patients with significant hospital exposure, studies at our institution [8] and others [9] have reported a high proportion of MRSA infections in patients without prior hospital exposure. Thus, MRSA has become clinically important in the management of community-associated as well as nosocomial infections.

Methicillin-resistance in S. aureus is associated with resistance to all β-lactam antimicrobials including penicillins and cephalosporins. In addition, MRSA isolates are often multiply resistant to antimicrobial agents of other classes [10, 11], including macrolides and fluoroquinolones, further limiting the arsenal of therapies. In fact, resistance to last-resort therapies such as vancomycin [12, 13] and linezolid [14] has already been reported, underscoring the urgency of efforts to characterize and contain this pathogen.

Despite a wealth of anecdotal evidence, the epidemiology of MRSA among pediatric surgical patients remains poorly characterized with no published reports of MRSA surveillance in the pediatric surgical literature. Therefore, we conducted a retrospective review of incision and drainage (I and D) procedures for soft-tissue abscesses at our institution from January 1998 through December 2004.

Materials and methods

We conducted a retrospective review of electronic medical records of 99 patients operated on at the University of Chicago Children’s Hospital for I and D of soft-tissue abscesses from January 1998 through December 2004. The study was approved by the University of Chicago Institutional Review Board. The University of Chicago’s Children’s Hospital is an urban, tertiary care medical center located in Chicago, IL, USA. The infection control policy for MRSA infections at our institution did not change during the study period. Patients with S. aureus isolates demonstrating resistance to methicillin were placed in isolation with contact precautions. Information regarding referral patterns during the study period was not available.

Statistical analyses were performed using Prism v4.01 (Graphpad Software, San Diego, CA, USA). Mean age and length of stay analysis was made using one-way ANOVA. Trends in number of isolates by year were analyzed with linear correlation. Contingency tables and chi-square analyses were used for analysis of prior hospitalization.

Results

Characteristics of patients and isolates

From 1998 through 2004, 99 pediatric patients received I and D drainage of soft-tissue abscesses at our institution. Isolates obtained from those procedures were organized by year of the procedure, culture results, and site of infection (Table 1). The number of I and D procedures per year increased during the study period from 5 in 1998 to 32 in 2004. There was no significant variation in length of stay (ANOVA, P=0.50) or patient age (ANOVA, P=0.88) with respect to year, organism, and site of abscess. Gram stain and culture were obtained for 90 patients, of which 79 (87.7%) were positive for growth. S. aureus (N=66) was the most commonly obtained isolate. Other isolates included coagulase-negative Staphylococci, Corynebacteria, Escherichia coli, Enterococcusfaecalis, and Group A Streptococcus. The most common sites of infection were extremities (upper and lower), groin, and buttocks.
Table 1

Isolate breakdown by year, organism, and site of abscess

Category

N

Mean patient age (months)

Mean LOS (days)

Year

 1998

5

55

3.6

 1999

7

48

5.3

 2000

5

66

4.4

 2001

4

73

3.3

 2002

16

69

8

 2003

30

59

3.3

 2004

32

37

2.7

Organism

 MRSA

52

40

3.4

 MSSA

14

49.3

5.3

 CoNS

4

136.5

1.75

 Other

9

121.5

6.5

 No growth

11

74.9

1.5

 No culture

9

56.6

9.8

Site of abscess

 Abdomen

7

92.2

3.8

 Buttocks

15

26.6

2.8

 Breast

8

50.7

3.7

 Groin

17

95.1

3.6

 Pilo

4

194.8

0.8

 Perineum

11

35.3

4.2

 Misc

12

31

3

 Perianal

6

49.8

2.2

 Ext

19

40.1

8.5

Other (organism) includes corynebacteria, Escherichia coli, Enterococcus faecalis, group A streptococcus; Other (site) hip, neck, occiput, suprapubic; N number of isolates, Age mean age of patient in months at time of procedure, LOS mean length of stay in days, MRSA methicillin-resistant Staphylococcus aureus, MSSA methicillin-sensitive Staphylococcus aureus, CoNS coagulase-negative staphylococci

Prevalence of MRSA among isolates

Methicillin-resistant Staphylococcus aureus was the most commonly obtained isolate for every year in the study period. The number of total isolates increased significantly during the study period (F=15.8, df=5, P=0.01), as did the number of MRSA isolates (F=16.8, df=5, P<0.01), with the largest increase from 2000 (N=3) to 2004 (N=20) (Fig. 1). Conversely, the number of methicillin-sensitive S. aureus (MSSA) isolates did not increase significantly during the study period (F=2.8, df=5, P=0.15). In particular, the number of MSSA isolates remained low from 2000 to 2004 when the total number of isolates and MRSA isolates substantially increased, reflecting an increasing proportion of methicillin resistance among S. aureus isolates.
https://static-content.springer.com/image/art%3A10.1007%2Fs00383-006-1684-x/MediaObjects/383_2006_1684_Fig1_HTML.gif
Fig. 1

The prevalence of MRSA, MSSA, and total isolates from I and D procedures for soft-tissue infections in pediatric patients: 1998–2004. Total total number of isolates obtained from I and D procedures, MRSA methicillin-resistant Staphylococcus aureus, MSSA methicillin-sensitive Staphylococcus aureus

MRSA is not associated with prior hospitalization

Methicillin-resistant Staphylococcus aureus has classically been recognized as a nosocomial pathogen. However, recent evidence suggests that MRSA strains have emerged in the community as well. Chart documentation of prior hospitalization was used to determine prior exposure to the hospital milieu. Information regarding prior hospitalization was available for 80 patients, among which only 25% had a prior hospitalization. The distribution of MRSA, MSSA, and other isolates was not significantly different for patients with a prior hospitalization compared with those without a prior hospitalization (χ2=1.47, df=2, P=0.48). Isolates among patients with a prior hospitalization were evenly distributed among MRSA, MSSA, and other pathogens (Fig. 2). Among patients without documented hospitalization, MRSA represented a much higher percent (51%) of isolates than MSSA (21%) or other organisms (28%). Furthermore, more than twice as many MRSA isolates were obtained from patients without prior hospitalization (N=22) than from patients with prior hospitalization (N=9).
https://static-content.springer.com/image/art%3A10.1007%2Fs00383-006-1684-x/MediaObjects/383_2006_1684_Fig2_HTML.gif
Fig. 2

Prevalence of MRSA, MSSA and other isolates by prior patient hospitalization. Other includes coagulase-negative staphylococci, corynebacteria, Escherichia coli, Enterococcus faecalis, group A streptococcus

MRSA is prevalent among all age groups

Isolates were stratified based on patient age into one of five groups to determine age-specific prevalence. MRSA isolates constituted ≥50% of isolates in all age groups, with the exception of patients 10–19 years of age (Fig. 3). Among infections in patients from that group, six different pathogens were represented, the highest number of different isolates from any age group. Among all age groups, MRSA constituted the largest proportion (0.75) of isolates from patients 1–3 years of age.
https://static-content.springer.com/image/art%3A10.1007%2Fs00383-006-1684-x/MediaObjects/383_2006_1684_Fig3_HTML.gif
Fig. 3

Methicillin-resistant Staphylococcus aureus prevalence after stratification by patient age

MRSA isolates are often cross-resistant to other antimicrobial agents

Many studies have reported high levels of resistance to non-β-lactam antimicrobials among MRSA isolates compared with MSSA isolates. We observed a similarly high level of cross-resistance to non-β-lactam antimicrobials among MRSA, but not MSSA isolates. Over 80% of MRSA isolates were resistant to erythromycin and over 90% were resistant to cefazolin (Fig. 4). Furthermore, 84.4% of MRSA isolates demonstrated resistance to both erythromycin and cefazolin. On the contrary, only 21.4% (3/14 isolates) of MSSA isolates were resistant to erythromycin, and none were resistant to cefazolin. Three MRSA isolates were resistant to clindamycin, each occurring in 2003. In each case, empirical treatment was changed to vancomycin (N=2) or linezolid (N=1) when sensitivities were determined.
https://static-content.springer.com/image/art%3A10.1007%2Fs00383-006-1684-x/MediaObjects/383_2006_1684_Fig4_HTML.gif
Fig. 4

A high proportion of co-resistance to multiple antimicrobials among MRSA isolates

Discussion

Methicillin-resistant Staphylococcus aureus has been a growing concern for surgeons for decades. Recent increases in its prevalence in some areas and changes in its epidemiology have mandated a renewed awareness of this pathogen. Although anecdotal evidence of its importance abounds, the role of MRSA specifically among pediatric surgical patients has remained poorly characterized in the literature. In this study we confirm that MRSA is prevalent among soft-tissue abscesses in pediatric patients at our institution and that the characteristics of MRSA isolates in our study are concordant with reported changes in its epidemiology.

We report an increasing prevalence of MRSA isolates among cultures from I and D procedures in pediatric patients, with the greatest increase occurring from 2000 to 2004. Importantly, most MRSA isolates were obtained from patients without a documented prior hospitalization. Although documentation of prior hospitalization is only a rough estimate of hospital exposure, the fact that such a large proportion of MRSA isolates were obtained from patients without prior hospitalization supports recent trends of this organism extending to the community setting.

Methicillin-resistant Staphylococcus aureus isolates demonstrated a high rate of co-resistance to non-β-lactam antimicrobials with over 80% expressing resistance to both macrolides and cephalosporins. Antimicrobials traditionally used for empiric management of soft-tissue infections, such as β-lactams and cephalosporins, may no longer provide sufficient coverage for empiric treatment of infections in communities where MRSA is prevalent. While some clinical scenarios may accommodate waiting for the results of culture and sensitivity testing, empiric management often necessitates initiating treatment before culture results and sensitivities are available. In such cases, alternative antimicrobials may be more appropriate to provide coverage for MRSA.

At our institution, clindamycin is frequently used for empiric treatment of soft-tissue infections when MRSA is suspected. Although we report three MRSA isolates resistant to clindamycin during the study period, alternative antimicrobials with superior coverage against MRSA, such as linezolid and vancomycin, should be reserved, as they represent a last line of defense against MRSA infections. Selecting an appropriate alternative agent will depend on the local epidemiology of MRSA in the community. Thus, it is important to know the local epidemiology of MRSA to make informed management decisions. Judicious use of antimicrobials and stringent infection control policies are imperative to control this organism, as few last-resort therapies are available [15].

The modest size and retrospective design of this study limit the extent to which our results can be generalized. Furthermore, we were unable to ascertain any changes in the referral pattern to our institution during the study period. Thus, it is unknown whether the increase in MRSA prevalence we observed was due to a widespread increase, or only a few isolated communities. Further studies of the epidemiology of MRSA isolates in our area are merited to address this concern. Antimicrobial resistance in S. aureus is a worldwide problem and varies greatly between regions. Until a larger, prospective study of MRSA isolates in pediatric surgical patients is available, the observations from our small, sentinel study will hopefully raise awareness of MRSA among pediatric surgeons in all settings.

Copyright information

© Springer-Verlag 2006