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Characteristics of Resistant Strains

Julian B. Orenstein, MD

Arch Pediatr Adolesc Med. 1996;150(8):809-814.

Abstract
Objectives
To review all cases of invasive Streptococcus pneumoniae infection at a single institution and to identify factors that may allow distinguishing between penicillin-resistant pneumococcal (PRP) and penicillin-sensitive pneumococcal strains at presentation for emergency care.

Patients and Methods
Consecutive patient series of all children with positive blood and cerebrospinal fluid cultures for S pneumoniae from January 1993 to April 1995 at a general community hospital.

Results
Fifty-three patients with invasive S pneumoniae infections were identified; 21% of the infections were resistant to penicillin, 9% were resistant to multiple antibiotics, and 4% were highly resistant to penicillin (minimum inhibitory concentration, >2 mg/L). At admission, a diagnosis of meningitis or sepsis was made in 14 patients; of these, 8 cerebrospinal fluid cultures yielded S pneumoniae, and 5 were PRP (P<.001). Significant differences between sensitive and resistant strains were not found for sex, age, race, ill household contacts, or physician type. Five of 11 children with PRP strains were either receiving antibiotics concurrently or in the prior 30 days compared with 5 of 42 children with penicillin-sensitive pneumococcal strains (P=.002). Children with PRP strains had a lower mean white blood cell count (14.9x10⁹/L vs 22.8x10⁹/L, P=.008) than children with penicillin-sensitive pneumococcal strains, owing to a lower mean absolute neutrophil count (7250 vs 12 700, P=.006). Children with lower white blood cell and absolute neutrophil counts did not, however, differ in other objective measures. Regression analysis showed that the combination of current or prior antibiotic use and an absolute neutrophil count predicted 63% of the resistant strains and 92% of the sensitive strains (P=.001).

Conclusions
A high proportion of S pneumoniae infections were caused by strains that were resistant to penicillin. We discuss factors that are associated with resistance in this population. The PRP strains were associated with recent antibiotic therapy and a low absolute neutrophil count. Further surveillance is warranted by these findings.

Arch Pediatr Adolesc Med. 1996;150:809-814

Author Affiliations
From the Departments of Pediatrics and Emergency Medicine, George Washington University, Washington, DC, and the Department of Emergency Medicine, Fairfax Hospital, Falls Church, Va.

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