INFECTIOUS DISEASE

Given their observations in group 1, the authors estimated that, on the basis of the initial screening tests at the referring institutions, approximately 196 (11.9%) of all patients in groups 1 and 2 would have elected abortion. By using confirmatory tests combined with counseling by a specialist, the authors were able to reduce the number of abortions from 196 to 53, a 73% decrease.

Always confirm an initial diagnosis

Given the ominous prognosis for congenital CMV infection and the major psychological implications and sobering finality of abortion, it is imperative that clinicians confirm the diagnosis of primary CMV infection. Because most cases of CMV infection in immunocompetent adults are asymptomatic, the diagnosis is typically confirmed by serology. Unfortunately, the serologic tests for CMV are not as straight-forward and reliable as tests for other viral infections such as rubella. Commercially available tests for anti-CMV IgM often have false-positive and false-negative results. In addition, IgM antibody may be detected as long as 9 months after a primary infection and may subsequently re-appear during reactivation of a latent infection or reinfection.^2,3

Be selective, on the basis of risk factors and clinical manifestations, when screening pregnant women for cytomegalovirus infection.

Routine screening is not necessary

The authors’ findings vividly illustrate the potential errors that can occur when a large number of asymptomatic patients are routinely screened for CMV. Because of these pitfalls, I do not recommend routine screening. Rather, screening should be selective, directed at women who:

• have clinical manifestations of CMV infection
• are immunosuppressed
• have small children in daycare or work in daycare themselves or
• have documented exposure to someone with CMV infection.

If the initial immunoassay for CMV IgM is positive, a confirmatory immunoblot test for IgM should be performed, as well as avidity testing for IgG.

If primary infection is confirmed, the patient should undergo targeted ultrasonography and amniocentesis to assess for manifestations of congenital infection and to detect CMV in amniotic fluid by culture or polymerase chain reaction (PCR) testing. If the sonogram shows signs of fetal injury, or the PCR test is positive, the woman should be counseled about the options, which include experimental immunotherapy with hyperimmune anti-CMV globulin⁴ and pregnancy termination.

The study by Guerra and colleagues is a welcome addition to the obstetric literature. By using a systematic diagnostic algorithm that included an enzyme-linked immunosorbent assay and an immunoblot assay for IgM antibody and avidity testing for IgG antibody, the authors were able to reclassify approximately 70% of patients as either uninfected or previously infected. As a result, they reduced the number of pregnancy terminations by 73%, an objective end-point that clearly has great social, economic, and medical impact.

Most community S. aureus infections are methicillin-resistant

Moran GJ, Krishnadasan A, Gorwitz RJ, et al. Methicillin-resistant S. aureus infections among patients in the emergency department. N Engl J Med. 2006;355:666–674.

Moran and colleagues reviewed the records of 422 adults with acute purulent and soft-tissue infections who were evaluated in 11 university-affiliated emergency departments in August 2004. Wounds were routinely cultured. When S. aureus was isolated, the organisms were tested for antimicrobial susceptibility to identify those that were methicillin-resistant. The PCR test was used to identify genes for staphylococcal enterotoxins A through E and H, toxic shock syndrome toxin, and Panton–Valentin leukocidin. The same methodology was used to identify the gene complex staphylococcal cassette chromosome mec (SCCmec). This complex contains the mecA gene that confers methicillin resistance.

Of the 422 patients, 320 (76%) had S. aureus isolated from their wound. The prevalence of methicillin resistance was 59%. Ninety-seven percent of MRSA isolates were pulsed-field type USA 300. SCCmec type IV and the Panton–Valentin leukocidin gene were detected in 98% of MRSA isolates. Other toxin genes were rare.

Only 2 drugs were 100% effective

Among MRSA isolates, 100% were susceptible to rifampin and trimethoprim-sulfamethoxazole (TMP-SMX), 95% were susceptible to clindamycin, and 92% were sensitive to tetracycline. Only 60% were sensitive to fluoroquinolones, and only 6% were sensitive to erythromycin. Only 43% of patients received initial empiric therapy with antibiotics to which their organisms were sensitive.

Reason to worry

S. aureus is an important pathogen in obstetric patients. It is the causative organism of toxic shock syndrome and the dominant pathogen in patients with puerperal mastitis, as well as one of the key causes of postoperative wound infection. When penicillin was developed in 1941, all strains of S. aureus were sensitive to the drug. Within a few short years, however, most hospital-acquired strains became resistant.

Methicillin was introduced in 1961 to treat these resistant staphylococcal species. Unfortunately, by the mid-1960s, methicillin-resistant S. aureus (MRSA) infections began to appear. By the 1990s, MRSA infections were common in hospitalized patients, particularly in intensive care units. Hospital-acquired MRSA isolates are often sensitive to only a few select antibiotics such as vancomycin, linezolid, and quinupristin/dalfopristin.⁵