Secondary infections in AD

Feb 18, 2015, 5:00am

Differential diagnosis is challenging in cases of secondary infections, including secondarily infected eczema in all its permutations.

Secondary infections vexing

Often at medical meetings, "people like to talk about fascinating, juicy infectious diseases" most dermatologists never see, says Sheila Fallon Friedlander, M.D., professor of clinical pediatrics and medicine (dermatology) at the University of California, San Diego.

However, she says, challenges that dermatologists face almost daily include secondary infections in atopic dermatitis (AD). In such cases, Dr. Friedlander says, it can be difficult to distinguish whether a patient is simply flaring, or suffering secondary infection.

To resolve this conundrum, "We look for t he classic signs of infection – honey-colored crust and oozing. But often, a patient won't have classic findings. In such situations, utilizing appropriate dry skin care and topical corticosteroids may be enough to clear the patient, even if S. aureus is cultured from the site. If that doesn't work, empiric antibiotic therapy may be the next best step."

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Research in this regard is "very interesting," she says. A large meta-analysis1 and several experts have stated that there is insufficient evidence to show a benefit of oral antibiotics in managing infected or uninfected eczema. However, says Dr. Friedlander, "This doesn't mean that antibiotics are ineffective. Many studies that have been performed are small and/or poorly designed."

Accordingly, says Dr. Friedlander, "When we treat patients, we try to use our head. We know that it's important, when in doubt and before instituting therapy, to obtain cultures because of the high incidence of MRSA nationwide, and to help guide appropriate therapy. It's equally important to use oral antibiotics only when you believe they are appropriate."

While awaiting culture results, she says, "If your community has a very high incidence of MRSA, as in Texas, use either clindamycin or Bactrim (sulfamethoxazole, trimethoprim; Roche). However, if you're in San Diego, where MRSA incidence is lower, particularly in patients with AD, we often start with a cephalosporin." Some physicians use clindamycin empirically, she says. But if a patient has no history of recurrent infections, and particularly no evidence of MRSA in any family contacts, "We'll start out empirically with cephalosporins."

In one case Dr. Friedlander presented, a boy was treated with sulfamethoxazole-trimethoprim for possible MRSA, but the next day, his mother reported that his skin looked worse. Cultures taken from his lesional skin grew Group A Streptococcus. In one review of children with AD who underwent skin cultures, investigators found that 16 percent had Group A strep, and 14 percent had evidence of both staph and strep.2

"A couple things are important here. First, the kids who have strep are more likely to be febrile, to have facial and perioral involvement and to be hospitalized, versus those with S. aureus alone." Second, Dr. Friedlander says, sulfamethoxazole-trimethoprim is ineffective against Group A strep.

"That's why we generally don't use Bactrim as first-line therapy in children who look well, unless I'm certain or highly suspicious that it's MRSA." Conversely, she says that clindamycin and cephalosporins cover both strep and most staphylococcal infections. "Some MRSA strains won't be covered by clindamycin, but many will."

NEXT: Bleach bath efficacy data

 

Bleach bath efficacy data

For patients with eczema who have chronic or recurrent staph infections, Dr. Friedlander says, many recent publications tout the benefits of bleach baths (lasting approximately 10 minutes) and other hygienic measures such as mupirocin ointment to the nares to help eliminate nasal carriage. In one study, twice-weekly bleach baths for three months led to a 20 percent decrease in staph infections.3 For teens who refuse bathing, she suggests bleach body washes and gels.

There's controversy about the right sodium hypochlorite concentration, however. "Many people use half a cup in a full 40-gallon tub, for a concentration of .0005 percent." Whether to rinse off the solution also is controversial. Here, she says, "I generally have kids rinse off, but this makes more work for mom. And no one has documented that it makes a difference. But one thing is clear: you'll want to grease them up with moisturizers when they get out."

Regarding bleach's mechanism of action, Dr. Friedlander says, "We know that bleach is antiviral, antifungal and antimicrobial." But a recent study shows that bleach also can inhibit inflammatory processes within the skin.4  "So it may be that these soaks are not only killing off bacteria, but also helping to decrease the inflammation."

In another common scenario, she says, an infant with a skin infection treated empirically with clindamycin may return two days later with homogenous-looking, highly erythematous lesions clustered mainly in the perioral area. "In this case, we must consider a virus. In fact, if we were to do a Tzanck stain of one of this child's lesions, we might see multinucleate giant cells," a hallmark of eczema herpeticum.

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"If we think a child has eczema herpeticum, we don't usually have time in clinic to do Tzanck stains. But I would suggest, if you can, that you obtain cultures or direct fluorescent antibody, which you can send off to a lab. A pearl that helps indicate you're dealing with a virus is that the lesions are almost always very monomorphic – like punched-out, crusted papules of similar size. Often, there is facial involvement."

Afflicted children need acyclovir (20 mg/kg four times daily; she uses the liquid formulation), Dr. Friedlander says. Usually, "These children are well enough to be treated as outpatients. When in doubt, cover for bacteria as well. It is often near-impossible to be sure whether you're dealing with a virus alone, or mixed infection."

Meanwhile, dermatologists' understanding of the role of S. aureus in AD keeps evolving. A recent study showed that S. aureus can elaborate a biofilm that obstructs eccrine ducts, resulting in miliaria.5 Dr. Friedlander says, "Some investigators now believe that may play a crucial role in the development of AD. Usually, we think of staph as a secondary phenomenon. But there's now some evidence that staph may have the ability to obstruct sweat glands, and this may be a pivotal event in the development of AD."

Regarding other conditions associated with AD, Dr. Friedlander says a recent case-control study provides early evidence of a link with molluscum contagiosum. Dermatologists have long suspected such a link, she says, but the evidence was very weak. "Now we have a somewhat better study that was performed in American Indians. It showed that molluscum contagiosum was more likely to have a prior or co-occurring diagnosis of eczema, scabies or some form of dermatitis compared to controls."6 Treatment options for patients with molluscum include cantharidin, cimetidine and cryotherapy, she says.

Drs. Friedlander and Tyring report no relevant financial interests. This article was assembled from presentations at MauiDerm, January 26-30, 2015, and supplemental interviews.

Next: References

 

References

Drs. Friedlander and Tyring report no relevant financial interests. This article was assembled from presentations at MauiDerm, January 26-30, 2015, and supplemental interviews.

1. Shams K, Grindlay DJ, Williams HC. Clin Exp Dermatol. 2011 Aug;36(6):573-7.

2. Sugarman JL, Hersh AL, Okamura T et al. Pediatr Dermatol. 2011 May-Jun;28(3):230-4.

3. Kaplan SL, Forbes A, Hammerman WA et al. Clin Infect Dis. 2014 Mar;58(5):679-82.

4. Leung TH, Zhang LF, Wang J et al. J Clin Invest. 2013 Dec 2;123(12):5361-70.

5. Allen HB, Vaze ND, Choi C et al. JAMA Dermatol. 2014 Mar;150(3):260-5.

6. McCollum AM, Holman RC, Hughes CM et al. PLoS One. 2014 Jul 29;9(7):e103419.

7. Downing C, Ramirez-Fort MK, Doan HQ et al. J Clin Virol. 2014 Aug;60(4):381-6.

 

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