Another Mosquito Bite...In the Middle of Winter?

Jennifer D. Nolt, MSN, CPNP; Sarah A. Martin, MS, RN, CPNP-PC/AC, CCRN; Terea Giannetta, MSN, RN, CPNP


J Pediatr Health Care. 2007;21(3):182-183, 211-21. 

In This Article

Questions and Answers

What differential diagnoses are you considering for this child?

The following are to be considered as possible diagnoses:

  • Recurrent bacterial skin infection

  • Recurrent fungal skin infection

  • An immune deficiency

  • Scabies

  • Poison oak/poison ivy

  • Erythema nodosum

  • Hidradenitis suppurativa

Considering the differential diagnoses for this patient will entail looking at various skin conditions, some of which are contagious, obtaining a thorough family history is imperative. The patient's mother reports similar lesions, and this information is helpful. The fact that two family members are experiencing similar lesions leads us to believe the entity is contagious, but the skin lesion distribution differs for E.M. and her mother.

Recurrent bacterial and fungal diseases are common and can be contagious, so these entities should be considered. Some immune deficiencies can present with recurrent skin lesions, but often, other signs are present. E.M. is growing well with normal milestone development. She does not have report of other types of recurrent infections. Although immune deficiencies cannot be ruled out by history alone, the possibility of this occurring in E.M. is not as likely.

Scabies is a common skin manifestation and often manifests in the diaper area in young children. One would expect manifestation along the ankle creases, wrist creases, and neck creases in a young child as well. In addition, one would expect family members to be complaining of skin lesions in their intra-digit regions, and the lesions would be described as extremely itchy. Because this history is not present, this condition is not likely.

Poison oak/poison ivy requires a recent travel history that E.M. does not have. In addition, if these entities were the etiology, one would expect the skin manifestations to occur on areas of the body that are exposed. Because E.M.'s lesions occur on her buttock and upper thigh regions, these conditions are not likely because she most likely wears a diaper and pants when she is outside.

Erythema nodosum most likely begins on the lower legs and does not discharge pus. The nodules often heal after passing through the various stages of bruising, and often, systemic symptoms such as fever are present. The distribution of lesions that E.M. is experiencing does not follow this pattern.

Hidradenitis suppurativa is a rare diagnosis that is more likely to appear in pubescent females. Lesions often appear in the axillary regions, pubic area, and under the breasts. E.M. is too young for this diagnosis, and her lesions are located primarily in the buttock area.

What diagnostic tests are being considered?

A wound culture and sensitivity needs to be performed to rule out bacterial and fungal etiologies. It is hoped that this test will provide etiological information for E.M.'s lesions. In addition, susceptibility information to antibiotics are provided, so this information is helpful in determining if the antibiotics that E.M. has taken have had any antimicrobial benefit.

Optimally, a culture is obtained from a lesion that has not discharged pus but is ready to do so. The lesion should be swabbed with alcohol and then lanced. Pus should be squeezed slowly. Pus that is first expressed is not the optimal culture material because it may be contaminated with skin flora. If a patient is taking antibiotics at the time, the wound culture may be sterile. One must remember, however, that resistant bacteria or fungal infections are not cured by commonly prescribed antibiotics, so a culture should be obtained despite the antibiotic history.

Culture and Susceptibility Data

Heavy growth of methicillin-resistant Staphylococcus aureus (MRSA) was detected with susceptibilities to clindamycin, bactrim, and vancomycin. The "D test" was negative for clindamycin.

A quick note on the "D test" or "disk diffusion test": Some laboratories automatically run this test once they determine that a culture is MRSA; other laboratories require a specific order for this test. The purpose of this test is to determine if the MRSA isolate has an inducible resistance to clindamycin. If the test is positive, then the isolate should be considered resistant to clindamycin. If the test is negative, then the isolate is susceptible to clindamycin.

What is your assessment and plan for E.M.?

E.M. has a painful, erythematous, warm buttock lesion that is not improving. She has taken multiple antibiotics in the past, and yet recurrent skin lesions continue to develop. She requires an incision and drainage procedure on the current skin lesion with a wound culture to determine the etiology. The incision and drainage procedure not only will provide culture information but also will provide pain relief because the pus can be drained. Following the incision and drainage, E.M. can be sent home with instructions to call if symptoms worsen and to come for follow-up in your office in 2 days. The family is given instructions to keep the lesion covered with clean gauze and engage in strict hand washing when touching the skin lesion.

E.M. returns to your office in 2 days for follow-up. The lesion site is beginning to scab, and there are no new lesions at this time.

What would be your recommendation for follow-up for this child?

No antibiotics are needed at this time. MRSA is common in community and hospital settings. MRSA accounts for as many as half of S aureus isolates at some institutions (Bertino, 1997). In most cases, patients have no known immune defect. The bacteria is resistant to certain antibiotics such as penicillin and cephalexin and is one of the most common causes of skin infections in America (Centers for Disease Control and Prevention [CDC], 2005). Skin infections are the most common, and most infections are minor, such as pimples and boils. MRSA also can cause more serious infections such as infections of surgical wounds and of the blood, bones, lungs, and central nervous system.

How Do You Counsel the Family About This Diagnosis?

The prevalence of MRSA is a social problem (Okano, Noguchi, Tabata, & Matsumoto, 2000). Prior to 1983, patients with MRSA were cared for in strict isolation in hospital settings, and the prevalence remained low. In 1983, however, new isolation guidelines recommended that patients with MRSA infections be cared for by using contact isolation (Boyce, Havill, Kohan, Dumigan, & Ligi, 2004). Since infection control measures became more lax, the prevalence of MRSA began to increase dramatically and continues to do so today.

MRSA infections are common in areas where crowding and close contact with others occurs, and MRSA spreads easily through households. Nosocomial risk factors include prolonged or recurrent antibiotic exposure, prolonged hospitalization, and hospitalization in an intensive care unit (Sattler, Mason, & Kaplan, 2002). Outpatient risk factors include chronic illnesses, residence in long-term facilities, recent admission to acute or chronic health care facilities, prior use of antibiotics or intravenous drug abuse, participation in sports teams (especially wrestling and football), participation in the military, being a health care worker or being in close contact with a health care worker, and residence or employment in a jail or day care setting.

The distinction between infection and colonization with MRSA must be made. Patients with an infection require treatment, but patients who are colonized may require no intervention. With regard to E.M.'s presentation, most skin infections with MRSA begin as a pimple or "mosquito bite." Some lesions drain and resolve, while others require surgical intervention and/or antibiotics. The first line of therapy is incision and drainage to determine the organism and susceptibility and to provide pain control, because the pus can be drained and healing can begin (Harrison, 2005). In E.M.'s case, her lesion is healing without the need for further intervention. If skin lesions continue to develop, incision and drainage procedures are first recommended because this method enhances healing without increasing resistance to further antibiotics. If there are multiple skin lesions and her MRSA isolate by culture report has shown her to be susceptible to clindamycin and bactrim in the past, then an oral course of either agent may be prescribed for a course of 5 to 10 days. Caution must be utilized with the use of clindamycin because of growing resistance to this agent (Martinez-Aguilar, 2003). If the lesion does not show signs of healing after the incision and drainage procedure, either oral antibiotic may be prescribed. Topical mupirocin ointment also can be placed on the lesion. For severe, life-threatening infections caused by MRSA, intravenous vancomycin may be used (Boyce, 2001).

Because E.M. is being treated for a MRSA skin infection, she is colonized with MRSA. About 1% of the population is colonized with MRSA where the bacteria is on the skin but is not causing an infection (CDC, 2005). Most persons colonized with MRSA are asymptomatic (Salgado, Farr, & Calfee, 2003). Therefore, acquisition of MRSA frequently goes unrecognized unless clinical infection develops. The anterior nares have been shown to be the main reservoir of S aureus in adults and children, and nasal carriage of S aureus has been demonstrated to be a significant risk factor for nosocomial and community-acquired infections (Nakamura et al., 2002). Half of those with nasal colonization also have colonization on their hands, making the unwashed hands the vectors for transmitting the pathogen (Bertino, 1997). Once on the skin, MRSA can enter the bloodstream through a wound and cause systemic infection. Multiple studies of infected patients demonstrated the same MRSA strain in both the nose and infection site, so eradication of nasal carriage with topical antimicrobials in most cases eliminated the organism from other body sites (Nakamura et al.).

In E.M.'s case, she could have become colonized by her mother because her mother is experiencing similar skin lesions and may have acquired this organism during her gastric bypass surgery, or E.M. could have become colonized by her father, who is working in the hospital setting where the likelihood of acquiring MRSA is high.

To decrease and attempt to eliminate the colonization of MRSA, decolonization methods may be tried. There is no guaranteed success of any method. Decolonization has not been generally recommended in the United States unless infections recur, or if an individual is at higher risk for serious infection as a result of diabetes, anticipating surgery, or immunosuppression, for example (Kemper, 2005).

One method of decolonization involves the application of gentian violet, a triphenylmethane antiseptic dye, at the site of skin lesions, as well as intranasally. The use of gentian violet in the treatment of superficial skin infections was suggested as early as 1912 because of its bactericidal properties (Okano et al., 2000). This method is inexpensive, but a major drawback is its staining effect.

Mupirocin is a naturally occurring antibiotic. Studies have utilized mupirocin intranasally, as well as topically to lesions. Efficacy in reducing MRSA colonization has been shown through the use of mupirocin intranasally twice daily for 5 days. Studies have demonstrated clearance of nasal cultures within 2 to 3 days, with 90% clearance by the end of 5 days. The most effective topical regimen for eradicating MRSA from the anterior nares has been intranasal application of mupirocin ointment (Boyce 2001, Chen 2005). There has been no evidence that extending the length of therapy beyond 5 days is beneficial, with the exception of investigational prophylaxis in hemodialysis patients, and prolonged therapy could increase the risk of mupirocin resistance (Bertino, 1997; Chen).

At the 25th National Pediatric Infectious Disease Seminar, Dr. Harrison spoke about the use of bleach baths for decolonization or to decrease skin colonization of MRSA. According to Harrison, the military employs this method with some success. For all household members, bleach baths should be used where for every gallon of bath water, a tablespoon of bleach is added. All household members with skin lesions should have these baths three times a week, while the rest of the household should have these baths at least once a week. Once all the skin lesions within the household have disappeared, the baths may be stopped (Harrison, 2005).

It was recommended that E.M. use the following methods: (a) intranasal mupirocin ointment and (b) bleach baths. Most likely, all of E.M.'s household is colonized with MRSA. As a practitioner, you could choose to test each individual for colonization by performing a nasal swab for MRSA. To decolonize, it is recommended that all family members at the same time engage in the decolonization process. The family can be given prescriptions to utilize intranasal mupirocin ointment twice a day for 5 days. This process can be repeated every 3 to 4 months if family members continue to present with recurrent MRSA skin lesions (Mody, Kauffman, McNeil, Galecki, & Bradley, 2003). In addition, all family members should use bleach baths as a means of decreasing or eliminating the surface colonization of MRSA.

In addition to decolonization methods, maintaining good hygiene and avoiding contact with open skin lesions are the primary means to prevent the spread of MRSA infections (Zinderman et al., 2004). Control measures such as frequent hand washing and the use of antibacterial hand sanitizers can decrease the spread of MRSA and should be employed.