June 1996
SAN FRANCISCO — The best offense can be good defense. Martin S. Cetron, MD, medical epidemiologist at the Centers for Disease Control and Prevention (CDC) discussed how the agency is combating the problem of drug resistant Streptococcus pneumoniae (DRSP). Cetron spoke recently at the annual meeting of American College of Physicians here.
A working group has made recommendations to curtail the spread of DRSP. These include: establishing laboratory-based surveillance; identifying risk factors and conducting research to establish the clinical outcomes of resistance; preventing disease through vaccination of recommended populations; and promoting the judicious use of antimicrobials.
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The CDC is working with others on these fronts. A comprehensive electronic surveillance system to analyze data about resistant isolates is being established. Hospitals and laboratories will be able to transmit antimicrobial susceptibility data for invasive pneumococcal isolates to the CDC and state and local health officials. CDC will analyze data on a national level and provide the results to clinicians so they will know the prevalence of DRSP in their communities. This will enable them to make informed decisions about prescribing antimicrobials. This electronic network is almost in place, Cetron said.
Representatives from several organizations, including the CDC, the Infectious Diseases Society of America and the American Academy of Pediatrics, have formed a committee to address therapy for DRSP infections. The committee, which met for the first time in April, is developing treatment guidelines for pneumococcal infections in the era of DRSP.
The CDC is also developing a parent information brochure to explain appropriate antimicrobial use. Parents need to understand that children who are not feeling well do not always require antimicrobials. It is hoped that this brochure, which will be available by the end of 1996, will help physicians, who feel pressured by parents to prescribe unnecessary antibiotics, to overcome that bias.
"It is our hope that by promoting judicious antimicrobial use and formulating treatment guidelines we may be able to curtail excessive antimicrobial use that has provided the selective pressure for resistance," Cetron said.
He outlined some risk factors for DRSP. Frequent antimicrobial use, including prophylaxis, is a strong predictor of DRSP. Another is day care center attendance. "This is a closed population of children who, because of their age and habits, tend to share respiratory secretions with agility. It is a population that frequently has respiratory infections and are frequently on antibiotics," he explained.
A child might acquire a resistant organism in the center; the organism then can spread from the child to other family members to the community.
"The clinical impact will become apparent in our most vulnerable patients initially, but will not necessarily be limited to them," Cetron said. Most vulnerable will be young children, the elderly, the immunocompromised, and others at risk for pneumococcal infections.
Whites with good access to health care are vulnerable to these isolates. The CDC tracked invasive pneumococcal infections in Atlanta. The isolates were serotyped and were tested for resistance.
"One of the striking things that we found was the disproportionate difference on white populations, compared with black populations in Atlanta," Cetron said. "We found about twice as high a risk of DRSP among the white populations than the black populations. If you look at the white children younger than 5 years of age, 56% of the invasive isolates were not susceptible to penicillin compared with only 17% in black children under 5."
He added, "One can only postulate that access to antimicrobials is a major risk factor in this."
Resistance is not limited to penicillin, Cetron pointed out. Resistance to cefotaxime, erythromycin, trimethoprim-sulfamethoxazole and chloramphenicol have been reported.
Also, the problem is not limited to pediatrics. "Those who are familiar with the DRSP story know that one of the risk factors has been young age and that DRSP emerged in the pediatric population first. My sense is that once DRSP became established within the community, it quickly spread to the adult population as well. By 1994, there was little difference in DRSP prevalence between children under 6 and adults 18 and over," he said.
Although non-susceptible isolates were seen as early as 1979, high-level resistance did not become a major problem until 1990, and there has been a sixtyfold increase within the last three years, he added. "Not only has the prevalence increased, but the number of serotypes that have been involved in resistant infections is growing. In the last three or four years over 20 different resistant serotypes of pneumococci have emerged," Cetron said.
Despite the increasing spread of DRSP, more than 90% of the resistant serotypes are currently included in the 23-valent pneumococcal vaccine. Unfortunately, the most recent data suggest that the vaccine is underused. Fewer than 20% of those targeted are immunized. "In the era of DRSP, primary prevention through vaccination remains one of our most effective weapons against pneumococcal infection," Cetron said.
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