INFECTIOUS DISEASE

In the late 1990s and early 2000s, MRSA began to appear in community-acquired infections in both adults and children. Most of these isolates have been implicated in skin and soft-tissue infections, but some have been responsible for invasive infection, bacteremia, and even death.⁶ Compared with hospital-acquired MRSA, these community isolates are more likely to be sensitive to commonly used antibiotics.

Always culture an infected wound

Knowledge of these sensitivity patterns is of great importance. Regrettably, as noted by Moran and associates, more than half of the patients (57%) were initially treated with antibiotics to which their infecting organism was resistant.

The clinical implications are clear:

• We must be aware that many community-acquired soft-tissue infections will be caused by drug-resistant staphylococci.
• Because antibiotic resistance is so prevalent, a culture of the infected wound should be obtained routinely so that antimicrobial therapy can be modified if the patient fails to respond to initial treatment.
• Antibiotic therapy alone is rarely sufficient for abscesses in the soft tissue and skin; adequate surgical drainage is essential.
• Fundamental infection-control measures, such as careful handwashing, adequate skin preparation prior to surgery, and local wound care, are of greater importance than ever.

Most cases of community-acquired MRSA have been isolated from skin and soft tissue; surgical drainage is necessary when infection advances to abscess in those sites.

In gravidas with group B strep, look for S. aureus

Chen KT, Huard RC, Della-Latta P, Saiman L. Prevalence of methicillin-sensitive and methicillin-resistant Staphylococcus aureus in pregnant women. Obstet Gynecol. 2006;108:482–487.

To assess the prevalence of methicillin-sensitive and community-acquired methicillin-resistant S. aureus colonization in pregnant women, Chen and colleagues evaluated de-identified culture specimens that had originally been submitted to the microbiology laboratory for identification of group B streptococcal infection. As opposed to hospital-associated MRSA isolates, community-associated methicillin-resistant strains were defined as those possessing the type IV or V staphylococcal chromosomal cassette mec element and lacking a multi-drug-resistant phenotype.

Of the 2,963 culture specimens in the prospective surveillance study, 743 (25%) were positive for group B streptococci, and 507 (17%) were positive for S. aureus. Group B streptococcal colonization was significantly associated with S. aureus colonization; the prevalence odds ratio was 2.1. Fourteen of the 507 S. aureus isolates were methicillin-resistant (2.8%; 95% confidence interval [CI] 1.4–4.2%). Thirteen of the 14 strains (93%) were community-acquired.

S. aureus may cause sepsis, wound infection, bacteremia, and other ills

The unique feature of this study is the observation that vaginal colonization with group B streptococci was significantly associated with colonization with S. aureus—one of the possible causative pathogens in chorioamnionitis, endometritis, wound infection, bacteremia, puerperal mastitis, and toxic shock syndrome. The organism also may cause serious neonatal infection, particularly sepsis.

The prevalence of group B streptococcal colonization in this study (25.1%, 95% CI 23.5–26.7%) is comparable to data reported from several other investigators.⁷ Colonized women are at increased risk for chorioamnionitis and puerperal endometritis, and their infants are at increased risk of sepsis, pneumonia, and meningitis. Fortunately, intrapartum antibiotic prophylaxis significantly reduces the risk of both maternal and neonatal group B streptococcal infection.⁸

As I noted earlier in this update, the antimicrobial susceptibility of S. aureus has become increasingly limited, particularly in light of the recent increase in both hospital- and community-acquired methicillin-resistant strains. In this study by Chen and colleagues, 2.8% of S. aureus isolates were methicillin-resistant. Of these, all but one were community-acquired.

Clinical suggestions

These findings certainly do not indicate the need for routine cultures for S. aureus vaginal colonization in all pregnant women. Nor are cultures needed in women who test positive for group B streptococci at 35 to 37 weeks. However, clinicians should be alert for possible staphylococcal infections, such as wound abscess, furuncle, carbuncle, or mastitis, in these women. If such an infection appears, obtain a culture of the purulent collection. Pending the result, treat the patient empirically with a drug that is likely to be effective against community-acquired MRSA. One hundred percent of these strains are sensitive to rifampin and TMP-SMX, and 90% to 95% are sensitive to tetracycline.⁹

Univalent HPV vaccine is 100% effective against CIN grades 2, 3

Mao C, Koutsky LA, Ault KA, et al. Efficacy of human papillomavirus-16 vaccine to prevent cervical intraepithelial neoplasia. Obstet Gynecol. 2006;107:18–27.

Mao and colleagues set out to assess the long-term protection of a univalent HPV vaccine against CIN grades 2, 3. Their prospective, randomized, double-blind, placebo-controlled trial involved 2,391 women, aged 16 to 23 years, who received either 40 μg of HPV-16 L1 virus-like particle vaccine or placebo intramuscularly at day 1, month 2, and month 6. Genital samples for HPV-16 DNA and cervical cytology specimens were collected at day 1, month 7, and then every 6 months for 48 months. A radioimmunoassay was used to assess antibody titers to HPV-16.