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MRSA-Related Abscess
By Michael L. Juliano, MD, LCDR/MC/USN, and Stephanie A. Dabulis, MD, LCDR/MC/USN
The authors discuss the alarming rise of methicillin-resistant Staphylococcus aureus in the community, as well as the risk factors for infection and the appropriateness
of antibiotic therapy.
Dr. Juliano and Dr. Dabulis are staff emergency physicians at the Naval Medical Center Portsmouth in Virginia. The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States Government. |
Cases of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) presenting to the emergency department continue to rise exponentially throughout the United States and worldwide. It is a serious public health issue that warrants the creation of standardized treatments and continued epidemiologic surveillance in order to modify recommendations as antibiotic resistance patterns change. The case presented here illustrates just one of the many ways in which the organism can be transmitted.
PATIENT PRESENTATION
A 16-day-old infant presents to the emergency department after her mother noted a red nodular area just to the right of the gluteal cleft the night before. The infant is asymptomatic and afebrile, with no decrease in feeding, activity level, or number of wet diapers. The mother reports that the child has no medical problems, is not being given any medications, has never received antibiotics, and has no known drug allergies.
The patient was born at full term via spontaneous vaginal delivery. The prenatal course was uncomplicated and the delivery uneventful, with no need for antibiotics. She was observed in the newborn nursery after delivery and was discharged from the hospital with her mother after approximately 36 hours.
The mother is the primary caregiver at home. The patient’s father recently returned from military duty in Iraq, six weeks prior to the child’s birth. While in Iraq, the father stayed in a barracks compound with shared bathing and exercise facilities. Both parents deny having experienced any lesions, sores, or abscesses in the past.
On physical examination, the baby appears healthy and active. Her rectal temperature is 97.3ºF, and her other vital signs are also normal. She weighs 7 pounds, 11 ounces. The skin lesion discovered by the mother is a 1.5-cm erythematous fluctuant mass, located at the top of the gluteal cleft and 2 cm right of midline. In the center of the lesion there is a 2-mm to 3-mm area that is pointing.
The patient is diagnosed as having an abscess. The diagnosis is explained to the mother and verbal consent is obtained for incision and drainage. The lesion is swabbed with alcohol and an 18-gauge needle is inserted into the center. Manual pressure is applied and 2 ml of purulent discharge is expressed. The fluid is sent for culture.
The mother is instructed to apply mupirocin ointment to the area as often as possible and to clean it twice daily with a chlorhexidine soap. Antibiotics are not prescribed due to adequate drainage of the abscess and the nonsystemic nature of the condition. The mother is further instructed to have a wound check performed the next morning either at her pediatrician’s office or in the emergency department.
A routine follow-up four days later, via telephone, reveals that the patient has had an almost complete resolution of the lesion. Culture results grew S. aureus that was resistant to cefazolin, erythromycin, oxacillin, and tetracycline.
DISCUSSION
Staphylococcus aureus isolates were uniformly sensitive to penicillin G until 1942. In 1959, the semisynthetic antibiotic methicillin was introduced. By 1961, the first cases of S. aureus being resistant to methicillin were reported. The term “methicillin-resistant Staphylococcus aureus” was coined following an outbreak at Boston City Hospital in 1968. Prior to 1997, MRSA was considered a nosocomial infection, generally not seen in patients without predisposing risk factors. In 1998, the first pediatric cases of CA-MRSA were reported in 26 otherwise healthy children. Since then, the prevalence of MRSA in the pediatric and adult populations has continued to increase and is now considered to be at epidemic levels.
A recent study by Hasty found an 80% prevalence of CA-MRSA in pediatric culture-positive abscesses at two geographically distinct pediatric emergency departments in the United States. A prospective screening program undertaken at an adult hospital showed a MRSA-positive rate of 6.7% for all admissions from the emergency department.
RISK FACTORS FOR MRSA INFECTION
Nosocomial risk factors associated with hospital-acquired MRSA (HA-MRSA) colonization and potential infection include prolonged or multiple hospitalizations or hospitalization in an ICU, close contact with a recently hospitalized individual, prolonged or recurrent antibiotic therapy, chronic illness, invasive procedures, and indwelling central catheters or other medical devices. Settings that carry a high risk of CA-MRSA include day-care centers, long-term care facilities, prisons, and military quarters (as in the case of the father in our patient presentation). Other risk factors include intrafamilial spread from contact with an MRSA carrier, HIV infection, and close contact among members of athletic teams.
Another emerging risk factor is a history of a previous MRSA infection of the skin or soft tissue. This became apparent during a recent influenza season, when cases of CA-MRSA pneumonia were reported in 10 patients aged 4 months to 48 years in Louisiana and Georgia. Four of these 10 patients had a previous history of an MRSA infection of the skin or soft tissue or contact with someone with an MRSA infection.
From the 1990s to the present, CA-MRSA has emerged as an established, community-based pathogen epidemiologically distinct from HA-MRSA. Today, CA-MRSA has become endemic not only in the community but also in the hospital setting. However, many patients, especially children, present to the emergency department with no identifiable risk factors for MRSA. In a retrospective cohort study, Zaoutis demonstrated no increased prevalence of CA-MRSA infections in children identified as having risk factors (hospitalization within the past year, indwelling medical devices, or chronic conditions) compared to those without risk factors. Similar conclusions were drawn by Fergie and Purcell, who performed a prospective observational study at the Texas Children’s Hospital. They found monthly rates of CA-MRSA of 35% to 51% in S. aureus isolates from patients with no significant risk factors for CA-MRSA infection.
In the future, the distinction between HA-MRSA and CA-MRSA may prove to be academic. The CA-MRSA pathogen has a type IV variation of the staphylococcal cassette chromosome containing the gene that confers methicillin resistance (SCCmecIV). These SCCmecIV genes are thought to incorporate fewer additional antibiotic-resistant genes than corresponding genes on HA-MRSA. Therefore, CA-MRSA lacks the multidrug-resistance rates of HA-MRSA strains. However, due to the inherent ability of all bacteria, especially S. aureus, to acquire new resistance patterns, increasing antibiotic resistance rates are occurring among strains of CA-MRSA.
Also, CA-MRSA infections are more likely to be cutaneous, causing furunculosis outbreaks, although reports of invasive and severe diseases such as necrotizing pneumonia and sepsis are on the rise. Ultimately, it may prove more useful to test for the presence of the virulence factor Panton-Valentine leukocidin (PVL), which elicits a group of more invasive symptoms, irrespective of where the infection was acquired.
The skin and mucous membranes are the first lines of defense against invading bacteria. Neonates, such as the patient presented here, are at increased risk for systemic infections with MRSA due to the immaturity of their epidermal barrier, which takes two to four weeks to attain full function but may take up to eight weeks in extremely premature infants. In a retrospective review, Mandel determined that a cutaneous abscess was the underlying cause in 22% of newborn infants with nosocomial sepsis.
ARE ANTIBIOTICS NECESSARY?
Several questions regarding treatment of a MRSA-related abscess remain unanswered, such as the necessity for antibiotics as an adjunct to incision and drainage. Adequate drainage is probably sufficient for complete resolution in most cases. Lee retrospectively reviewed 69 children with CA-MRSA abscesses. All received antibiotics (93% of them received an antibiotic that was ineffective against MRSA); however, only four patients (6%) required hospitalization on follow-up. After culture results became available, only 36% of patients were switched to an antibiotic active against CA-MRSA. The authors found no significant difference in response between patients who did receive antibiotics active against CA-MRSA and those who did not.
Another study found that 29 children with cutaneous MRSA infections improved despite treatment with ineffective antibiotics (although 11 patients also underwent incision and drainage). A similar study in San Francisco showed that of 146 adult patients who underwent incision and drainage for an MRSA abscess (the majority of whom were injection drug users or homeless, or both), 30% received an antibiotic ineffective against MRSA, and yet the infections resolved in every case.
Both HA-MRSA and CA-MRSA were previously distinguished by their antibiotic susceptibility pattern. A local antibiogram and surveillance program in the community is helpful for treatment options. For localized infections of cellulitis where the patient appears well, trimethoprim-sulfamethoxazole plus rifampin is the treatment of choice.
Oral clindamycin is another treatment option for outpatients. However, many strains of CA-MRSA have shown inducible resistance to clindamycin, particularly if the isolate demonstrates erythromycin resistance. Therefore, clindamycin monotherapy should be avoided in any clinically ill patient until inducible clindamycin resistance has been excluded by double disk testing.
In children who require inpatient management for systemic disease, such as necrotizing fasciitis, pneumonia, or osteomyelitis, vancomycin is generally considered the first choice along with a third-generation cephalosporin until antibiotic sensitivities are known. The number of case reports of vancomycin, linezolid, and daptomycin resistance, however, is increasing.
The box below summarizes the therapeutic options for MRSA.
OPTIMAL STRATEGY
The optimal strategy for controlling MRSA has yet to be determined. Some strategies include eradicating colonization. In Nashville, there has been a 10-fold increase in the MRSA colonization rate. A recent treatment combining skin disinfection and nasal mupirocin appears to be effective in decolonization and preventing recurrences. However, cases of mupirocin resistance also are emerging. Chen demonstrated that the use of topical mupirocin eradicates the carrier state; however, recolonization recurs within a short time.
Concomitant infection control measures may be equally, if not more, important. Hospitals around the world continue to attempt to demonstrate that MRSA can be controlled by an aggressive infection control program in addition to an active surveillance program. In an adult ICU setting, a prospective study looked at new MRSA infections after isolation and antimicrobial procedures were initiated for all new MRSA-positive admissions. The antimicrobial procedures included daily chlorhexidine baths and nasal mupirocin treatment. New ICU cases of MRSA declined from 15% to 5%.
Such aggressive control programs may prove cost-effective in the long run, due to the high cost of treating patients with MRSA is higher because of medications, length of stay, and isolation measures. In addition, strategies that support standardized treatments and continued surveillance can prevent the unnecessary use of antibiotics in order to deter future resistance.
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Suggested Reading
Chen AE, et al.: Evolving epidemiology of pediatric Staphylococcus aureus cutaneous infections in a Baltimore hospital. Pediatr Emerg Care 22(10):717, 2006.
Creech CB 2nd, et al.: Increasing rates of nasal carriage of methicillin-resistant Staphylococcus aureus in healthy children. Pediatr Infect Dis J 24(7):617, 2005.
Elston DM: Community-acquired methicillin-resistant Staphylococcus aureus. J Am Acad Dermatol 56(1):1, 2007.
Hasty MB, et al.: Cutaneous community-acquired methicillin-resistant Staphylococcus aureus among all skin and soft-tissue infections in two geographically distinct pediatric emergency departments. Acad Emerg Med 14(1):35, 2007.
Herold BC, et al.: Community-acquired methicillin-resistant Staphylococcus aureus in children with no identified predisposing risk. JAMA 279(8):593, 1998.
Jensen AG, et al.: Risk factors for hospital-acquired Staphylococcus aureus bacteremia. Arch Intern Med 159(13):1437, 1999.
Larson AA and Dinulos JG: Cutaneous bacterial infections in the newborn. Curr Opin Pediatr 17(4):481, 2005.
Lee MC, et al.: Management and outcome of children with skin and soft tissue abscesses caused by community-acquired methicillin-resistant Staphylococcus aureus. Pediatr Infect Dis J 23(2):123, 2004.
Mandel D, et al.: Nosocomial cutaneous abscesses in septic infants. Arch Dis Child Fetal Neonatal Ed 89(2):F161, 2004.
Mongkolrattanothai K, et al.: Severe Staphylococcus aureus infections caused by clonally related community-acquired methicillin-susceptible and methicillin-resistant isolates. Clin Infect Dis 37(8):1050, 2003.
Nakamura MM, et al.: Prevalence of methicillin-resistant Staphylococcus aureus nasal carriage in the community pediatric population. Pediatr Infect Dis J 21(10):917, 2002.
Sattler CA, et al.: Prospective comparison of risk factors and demographic and clinical characteristics of community-acquired, methicillin-resistant versus methicillin-susceptible Staphylococcus aureus infection in children. Pediatr Infect Dis J 21(10):910, 2002.
Segreti J: Efficacy of current agents used in the treatment of Gram-positive infections and the consequences of resistance. Clin Microbiol Infect II (Suppl 3):29, 2005.
Singer J, et al.: Emergency department perspective on methicillin-resistant Staphylococcus aureus. Pediatr Emerg Care 22(4):270, 2006.
Zaoutis TE, et al.: Clinical and molecular epidemiology of community-acquired methicillin-resistant Staphylococcus aureus infections among children with risk factors for health care-associated infection: 2001-2003. Pediatr Infect Dis J 25(4):343, 2006.
Zetola N, et al.: Community-acquired methicillin-resistant Staphylococcus aureus: an emerging threat. Lancet Infect Dis 5(5):275, 2005. |
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