Loretta Wubbel

Etiology and treatment of community-acquired pneumonia in ambulatory children.

OBJECTIVES To determine the etiology of community-acquired pneumonia in ambulatory children and to compare responses to treatment with azithromycin, amoxicillin-clavulanate or erythromycin estolate. METHODS Ambulatory patients with pneumonia were identified at the Childrens Medical Center of Dallas, TX. Children age 6 months to 16 years with radiographic and clinical evidence of pneumonia were enrolled and randomized to receive either azithromycin suspension for 5 days or a 10-day course of amoxicillin-clavulanate for those <5 years or erythromycin estolate suspension for those > or = 5 years. Blood culture was obtained in all patients and we obtained nasopharyngeal and pharyngeal swabs for culture and polymerase chain reaction (PCR) testing for Chlamydia pneumoniae and Mycoplasma pneumoniae and nasopharyngeal swabs for viral direct fluorescent antibody and culture. Acute and convalescent serum specimens were tested for antibodies to C. pneumoniae, M. pneumoniae and Streptococcus pneumoniae. Patients were evaluated 10 to 37 days later when repeat specimens for serology, PCR and culture were obtained. For comparative purposes healthy children attending the well-child clinic had nasopharyngeal and pharyngeal swabs obtained for PCR and culture for C. pneumoniae and M. pneumoniae. RESULTS Between February, 1996, and December, 1997, we enrolled 174 patients, 168 of whom fulfilled protocol criteria for evaluation. There were 55% males and 63% were <5 years of age. All blood cultures were sterile and there was no correlation between the white blood cell and differential counts and etiology of pneumonia. Etiologic agents were identified in 73 (43%) of 168 patients. Infection was attributed to M. pneumoniae in 7% (12 of 168), C. pneumoniae in 6% (10 of 168), S. pneumoniae in 27% (35 of 129) and viruses in 20% (31 of 157). None of the swab specimens from 75 healthy control children was positive for C. pneumoniae or M. pneumoniae. Clinical response to therapy was similar for the three antibiotic regimens evaluated, including those with infection attributed to bacterial agents. CONCLUSION Although a possible microbial etiology was identified in 43% of the evaluable patients, clinical findings and results of blood cultures, chest radiographs and white blood cell and differential counts did not distinguish patients with a defined etiology from those without a known cause for pneumonia. There were no differences in the clinical responses of patients to the antimicrobial regimens studied.

Mycoplasma pneumoniae Pneumonia in a Mouse Model

To investigate the pathogenesis of acute Mycoplasma pneumoniae infection, BALB/c mice were anesthetized with metofane, and M. pneumoniae was introduced intranasally on days 0, 1, and 2. Mice were sacrificed on days 0-15. A histopathologic scoring system defined inflammatory changes in the lungs on a scale of 0-26 (least to most severe). Broth cultures were positive for all nasal passage and bronchoalveolar lavage (BAL) specimens. Histopathologic scores ranged from 0 to 21. The mean log10 (cfu/mL) were 4.1-6.4 on days 1-10 and >/=1.7 on days 13-15 for nasal passage and BAL specimens. Serum polymerase chain reaction was negative. ELISA for serum IgM and immunoblots for M. pneumoniae antibody were positive in 21 (62%) of 34 and 33 (97%) of 34 infected animals, respectively, at days 8-15. ELISA for IgG antibody was negative. This mouse pneumonia model can be used to study the immunologic and therapeutic responses to acute M. pneumoniae infection.

Buffy coat PCR for diagnosis of experimental pneumococcal pneumonia

An immunocompetent murine model of pneumococcal pneumonia and bacteremia was used to evaluate a PCR assay based on amplification of the pneumolysin gene. Mice were treated with trovafioxacin to determine the decline in sensitivity of PCR as lung bacterial concentrations decreased and blood cultures became sterile. Forty‐three mice were studied for up to 120 h after start of antibiotic treatment. PCR of buffy coat specimens was more sensitive than PCR of plasma. Only 21% of animals had a positive blood culture, whereas 77% of PCR buffy coat assays were positive. After 48 h of therapy all blood culture specimens were sterile, whereas buffy coat PCR was positive in 57.8% of specimens. PCR of buffy coat specimens was negative in all mice colonized nasally with Streptococcus pneumoniae and in rabbits with Escherichia coli bacteremia. Our results demonstrate that our PCR technique using buffy coat specimens is highly specific for invasive pneumococcal disease and remains positive in the majority of animals for at least 48 h after start of antibiotic therapy.