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New Treatments for Impetigo and Skin Infections

This talk will be on skin and soft tissue infections. The way I will break this down is sort of anatomically - going through infections spreading from outer layers of the skin to deeper layers of the skin, subcutaneous fat and tissue and then fascia and muscle. Along the way, we will talk about some specific clinical situations as well, including diabetic foot infections.

We'll start with the outer layers. Impetigo, which is a very common superficial skin infection, is almost always caused by either group A beta hemolytic streptococci or Strep pyogenes or Staph aureus and may be a mixture of those two organisms. It is more common in children and it is more common in warmer weather, although it can occur year-round, and it certainly can occur in adults. The major mimic and the major differential diagnostic piece here is differentiating it from cutaneous herpes infection.

Most commonly, the organisms come from a colonized pharynx. The clinical scenario is that someone presents with a pharyngitis, either symptomatic or asymptomatic, that won't bring someone to medical attention but that you can elicit historically when you are seeing them with the rash and you suspect impetigo. But most likely, that is where the organism comes from; it is someone who has it in their throat and then spreads it to their skin. The reason it causes an infection is because of micro breaks in the skin.

Impetigo is incredibly contagious. It spreads very rapidly from person to person. If you are dealing with children in day care centers where one kid has it, then a lot of the rest of the kids in the group are going to have it, but it can also spread in households.

The treatment of this infection is usually now a combination of things. With the availability of topical mupirocin, or Bactroban, this is a very effective topical agent against both group A strep and staphylococci. So this is a very useful adjunct in the treatment and sometimes can be used as the only treatment for impetigo. Most people, however, combine topical agents with oral agents. Most group A strep - the vast majority of group A strep, remain very sensitive.

Erysipelas is also a streptococcal infection and it is an infection a little bit deeper down; it is an infection of the superficial dermis due to streptococci, almost always group A strep. The more unusual ones are due to non-group A beta hemolytic streptococci. You can see an erysipelas-like disease due to group B strep, group C strep, occasionally even some of the other beta hemolytic streptococci, such as group G strep.

These people, in contrast to people with impetigo, where constitutional symptoms are either mild or absent, commonly have constitutional symptoms. Those symptoms can be severe - people can be very sick with erysipelas. They can have fever, shaking chills and pain in the region. This is the occasion where sometimes when you think about treating.

In terms of anatomically, you usually see this on the extremities, but it may occur on the face in about ten percent of cases. I've seen this a few times, including in some colleagues who I've worked with, where they are on rounds in the afternoon and have a little bit of irritation on their nose; they scratch their nose and then during the course of afternoon rounds.

When you see someone with a lower extremity cellulitis, erysipelas or any kind of skin infection, particularly if it is recurrent, look for athlete's foot, because if you see it, you can treat that and decrease their risk of a recurrent skin infection. As I mentioned, this is true in wounds as well. Erysipelas, as I said before, is usually a clinical diagnosis. Therapy depends on how sick somebody is. There are not clear guidelines for this; this is a clinical judgment call.

The next layer down is cellulitis. Cellulitis involves all layers of the skin to the subcutaneous tissue. It is also a clinical diagnosis. It is a spreading, warm, flat, red area. The systemic symptoms that are associated with cellulitis are variable and can range from none to severe. This really not only depends on the bacteria that is causing it, but also the underlying host, how long the infection has been going on and a lot of other things.

Let's talk about a subset of this, a diabetic foot infection. So now we are extending cellulitis potentially down further when we talk about this. The risks for disease after local trauma, which may be minor, for example, rubbing against a new shoe, which allows minor skin breakdown but can allow organisms to get in, and because there is an abnormal blood supply due to the peripheral vascular disease which is very common in diabetics, those organisms are allowed to set up shop and cause infection. Diabetics are at increased risk for trauma because neuropathy is very common, so they may not feel the fact that their shoe is rubbing against their foot and that is what puts them at risk for the local trauma. Prevention here is extremely important.

Necrotizing fasciitis is an acute clinical presentation. These people are systemically ill. The hallmark of this illness is extreme pain. This is pain out of proportion to clinical appearance. Just like ischemic colitis, where you think about pain out of proportion to exam, here when someone complains of extreme pain in their extremity and they have a little cellulitis or a little bit of redness on their leg but their pain is really out of proportion to that, one of the things you would think of is whether the infection may be deeper than it looks. Another thing might be what is going on with the vascular system and is there vascular insufficiency.

I would like to say a few words about bite wounds - animal and then human bites. Fifty percent of U.S. citizens will have at least one animal bite throughout their lifetime; this is a very common occurrence. It accounts for about one percent of all emergency room visits and anatomically occurs on the hands and face most often. The bacterial flora depends on what the animal is. You will need to know specific animals and what the organisms are.

When do you give prophylaxis for animal bites? You usually do it for wounds on the hands, near the joints, on the genitals or with bad crush injury. You don't need it for bites of greater than 24 hours' duration. If the bite occurred two days ago and there is no sign of infection, you don't need to do it. In general, if prophylaxis is given, it is continued for three to five days.

Now a word about human bite wounds. The mechanism of injury is usually clenched fist as part of a fight or self inflicted. Bacterial flora is human mouth flora. The unusual organism here is an oral anaerobe called Eikenella and skin flora as well. The rate of infection with human bite wounds is higher than with animals. Surgical treatment is the most important thing. Prophylactic antibiotics are usually given due to the higher rates of infection; so that is the difference between human and animal bites. Because the risk of infection is higher, you generally treat for three to five days. If the injury is on the hand, patients are hospitalized.