Multiple Antibiotic Resistance

Multiple Antibiotic Resistance

Background: Penicillin-resistant strains of Streptococcus pneumoniae are present across the United States. The alteration in penicillin-binding proteins that mediate resistance to penicillin can also lead to reduced susceptibility to other B-lactam antibiotics and to high rates of resistance to other antibiotics. Most studies have focused on children in urban areas, but this surveillance study targeted isolated rural populations of healthy children, seeking to determine the prevalence of pneumococcal resistance to identify factors predictive of pneumococcal carriage.

Methods: Community A in Utah enrolled 177 families with 368 children (mean age, 5.0 years); community B (also Utah) included 212 families with 369 children (mean age, 5.1 years). Surveillance cultures were obtained from children younger than 8 years, and questionnaires and local pharmacy records supplied data relative to antibiotic use and presence of other risk factors. The isolates from the children were tested for susceptibility to penicillin, cefaclor, trimethoprim-sulfamethoxazole, erythromycin, ceftriaxone, and trovafloxacin. For selected resistant isolates, testing included serotyping, pulsed field gel electrophoresis, and Southern blot analysis with DNA probes specific for the pneumococcal lytA gene and for antibiotic-resistant genes.

Results: Children from community A had fewer antibiotic cours per child during the preceding year than those from community B, and oral cephalosporins were used more often in community A (22%) than community B(12%). Surveillance cultures found colonization with S pneumoniae in 24% of children from community A and 14% of those in community B. Intermediate resistance or greater to one or more antibiotics was detected in 34% of the isolates from community A and 24% of those from community B. Antibiotics to which these children were most often less susceptible were trimethoprim-sulfamethoxazole and cefaclor. Risk factors for colonization with S pneumoniae includid age less than 5 years, exposure to child care, number of children 8 years or younger in the family, and presence of a sibling with a positive culture. High colinearity was found between the presence of a sibling with a positive culture and family size. Antibiotic treatment was not an independent risk factors for pneumococcal carriage. For colonization with resistant S pneumoniae, risk factors were use of cephalosporins in the preceding 4 months, age younger than 2 years, and a sibling with a positive culture for resistant S pneumonia. Analysis of sibling pairs for resistant isolates showed that the isolates were identical in susceptibility interpretive class and within one dilution difference of each other in terms of the minimum inhibitory concentration for each antibiotic evaluated. Several pneumococcal isolates shared the molecular characteristics of international clones of pneumococci that have been spread worldwide and are resistant to multiple drugs.

Conclusions: The community in which cephalosporins were used most had an elevated rate of resistant pneumococcal carriage, but overall the rate of pneumococcal carriage was high. Exposure to cephalosporins showed an independent relationship with carriage of resistant pneumococci. Risk factor analysis found sibling transmission heavily contributed to the dissemination of organisms. Reduction in overall antibiotic usage for unsupported indications should be promoted as a preventive action against further development of resistant organisms.