July 2001

A 5-year-old boy was referred from a regional clinic for admission to the hospital for evaluation and treatment of a painful, swollen and erythematous left knee. The problem began about 3 weeks earlier with a pruritic, papular rash over the legs with scattered lesions on the arms and trunk. His mother does not know of any precipitating cause except possible mosquito bites. The child was initially treated for impetigo with oral cephalexin. After no improvement he was treated for scabies with 5% permethrin cream, and continued on the antibiotic, again without improvement.

His past medical history was unremarkable, and immunizations were up to date. His family history was also normal with no one else at home with a similar problem. There’s been no, camping, trauma, tick bites or exposure to wild or sick animals. As noted above, there may have been mosquito bites initially, but no one else in the family got any bites. However, there was some travel, as he did visit relatives in Arkansas just prior to the onset.

Examination revealed a healthy-appearing boy with a red, swollen, and moderately painful left knee with numerous excoriated papular lesions on the legs, arms and trunk as shown in figures 1–4 (note in figure 1 his tattoo from his days in the Navy; just kidding). Radiographs of the knees and surrounding osseous structures were normal with good range of motion testing, which did not worsen the pain. A lesion with superficial underlying fluctuance lateral to the left knee was incised and drained, producing 7 ml-10 ml of pus containing numerous gram-positive cocci in clusters.

He was treated with nafcillin IV with some minimal improvement, which seemed to be more associated with the drainage procedure.

What’s Your Diagnosis?

1. Infection due to resistant bacteria
2. Septic arthritis of the knee
3. Septic prepatellar bursitis
4. Osteomyelitis

Answer

The answer is #1, cellulitis with abscess due to resistant bacteria. In this case it turned out to be methicillin-resistant Staphylococcus aureus (MRSA). The main concern with this case was that the organism was community-acquired. We are seeing more and more patients admitted to the hospital with community-acquired MRSA (CAMRSA) infections that previously were easily treated with oral anti-staph penicillins or cephalosporins. This unsuspected resistance obviously allows the progression of the staph infection to advance unabated to the point of requiring admission to the hospital. We have had 2 cases of osteomyelitis with septic arthritis (figures 5-11) and one case of bacteremia (figure 12) admitted for treatment of CAMRSA during this past year. Figures 5-9 are the same patient. Note the multifocal osteomyelitis involving the proximal tibia in figures 5&6 and the proximal femur on the MRI scan in figure 7. Also, one can see the bulging of the joint capsule of the knee in figure 5.

Initial cause

Each of these cases started just like the patient presented above, with simple impetigo that progressed over a couple of weeks time to become more invasive due to ineffective therapy. These are excellent examples of the complications associated with the growing problem of antimicrobial resistance. Many of our colleagues are not worried about bacterial resistance because there is almost always another new wonder drug or combination product that will treat the patient standing (or lying) before them. And that’s true. The problem is, there is greater potential for injury to the patient who is unfortunate enough to be infected with one of these resistant organisms while waiting for culture and sensitivity results. The vast majority of antimicrobial therapy is initiated as empiric therapy based on the most likely cause(s). Patterns of resistance ultimately will dictate the empiric therapy we use. However, broadening this empiric therapy also feeds this vicious cycle of more resistance.

According to Jay M. Lieberman, MD, at the University of California, Irvine, in 1941, all strains of Staphylococcus aureus were sensitive to penicillin. At the Third Annual Infectious Diseases in Children Seminar West last month, Dr. Lieberman noted that by the mid-1940’s, penicillinase (b-lactamase) was identified, and by 1960, more than 90% of all S. aureus isolates were resistant to penicillin, which remains about the same today. This obviously helped fuel the development of b-lactamase resistant penicillins and the first-generation cephalosporins. While we are not seeing the emergence of CAMRSA at that rate of speed, it is none-the-less gaining momentum, and is beginning to have an impact on the empiric therapy of certain high-risk patients. For example, our oncologists now routinely use vancomycin, rather than nafcillin or methicillin, as part of the empiric therapy of our febrile neutropenic cancer patients admitted to the hospital. Some questions that bear some thought are:

How long will it be before we have to resort to more expensive and more toxic alternative choices for common outpatient staph infections?

How long will it be before we are saying the same thing about vancomycin and inpatient MRSA infections?

And as it becomes more common, how long will it remain appropriate to continue enforcing contact isolation precautions for inpatients with MRSA colonization or infection? The answer to all 3 is "not long." Many strains of CAMRSA will be sensitive to clindamycin (Cleocin, Pharmacia), which can be given orally for relatively minor, outpatient infections. It can also be used for continuation of therapy in patients being discharged from the hospital. However, there is one caveat with the use of clindamycin. If the MRSA is sensitive to clindamycin, but resistant to erythromycin, beware of developing resistance to clindamycin and treatment failure.

The patient presented was treated with clindamycin with good results. With regard to the other choices, septic arthritis and osteomyelitis might have normal or abnormal radiographs (as shown above), but would have likely had more pain on exam and range of motion testing. Plus, the relief achieved from draining the superficial cutaneous abscess would seem to rule against a deeper infection.

Prepatellar bursitis may look very similar to the knee of this patient. However, the swelling would have been located over the top of the knee with a more domed appearance (figures 13–16, and 17&18 from another patient) rather than diffuse and off to one side. It is also most commonly a Staph aureus infectious complication of an injury to the knee. It is often associated with only minimal pain, as seen in this patient. For those of you who keep these columns, this condition was featured in the December 2000 issue of Infectious Diseases in Children.

Tribute to a colleague

Figures 17 & 18 are courtesy of Many strains of CAMRSA will be sensitive to clindamycin (Cleocin, Pharmacia), which can be given orally for relatively minor, outpatient infections. It can also be used for continuation of therapy in patients being discharged from the hospital. However, there is one caveat with the use of clindamycin. If the MRSA is sensitive to clindamycin, but resistant to erythromycin, beware of developing resistance to clindamycin and treatment failure. of Honolulu, Hawaii. Over the last 4 decades, Dr. Bass has generously shared literally hundreds of clinical photographs with many colleagues. I was very fortunate to have a large part of his collection copied with his permission. Many of these have, and will continue, to appear in this column as long as I am writing it. I am very sad to report that Col. Bass died of infectious complications of cancer in the very early morning hours of June the 12th at his home in Honolulu. Time constraints of publishing this issue prohibits writing more about Dr. Bass at this time. Look for a more appropriate tribute in next month’s issue.

For Your Information:

• James H. Brien, DO, Pediatric Infectious Disease, Scott and White's Children's Health Center and Texas A&M University, College of Medicine, Temple, Texas. E-mail: jhbriend@aol.com