Legionella and community-acquired pneumonia: a review of current diagnostic tests from a clinician's viewpoint.

Many physicians are unaware of the limitations of the available tests for diagnosing infections with Legionella organisms. Geographic differences in the importance of nonpneumophila Legionella species as pathogens are underrecognized, in part because available diagnostic tests are biased toward the detection of pneumophila serogroup 1. Routine laboratory practices reduce the likelihood of culturing Legionella species from clinical isolates. Failure of seroconversion is common, particularly with nonpneumophila species; even when seroconversion occurs, it may take much longer than 4 weeks. Urinary antigen testing has insufficient sensitivity to affect clinical management in most regions of the United States, as it can reliably detect only L. pneumophila serogroup 1 infections. Polymerase chain reaction-based techniques offer hope of providing highly sensitive, rapid diagnostic tests for all Legionella species, but limitations in the current tests will make validating them difficult.

Pneumonia in the immunocompromised host: the role of bronchoscopy and newer diagnostic techniques.

The microbiology laboratory plays an essential role in the laboratory diagnosis of pneumonia in the immunocompromised host. Both the diversity of underlying or predisposing host conditions that increase risk for pneumonia and the variety of microbial agents that may be etiologically responsible make the laboratory's role in the diagnostic process a challenging one. In addition, the laboratory has a number of diagnostic tools available for detection of etiologic agents including conventional stains and cultures as well as newer tests relying on antigen detection and molecular techniques. Respiratory specimens available for testing are also diverse and are often obtained by the use of fiberoptic bronchoscopy, but may be complemented by use of blood samples when dissemination is likely or more recently by urinary antigen testing in select cases. Given the large number of variables in the design of a diagnostic approach to pneumonia in the immunocompromised host, it is critical that laboratorians and clinicians cooperate in the development of protocols that are cost effective and appropriate to their specific clinical settings.

The role of molecular diagnostics in the clinical microbiology laboratory.

With the exquisite sensitivity, inherent specificity, and versatility of polymerase chain reaction (PCR) and other amplification techniques, it is clear that infectious disease diagnostic tests based on these methods will assume a niche quickly in many clinical microbiology laboratories. Routine implementation, however, requires that many issues be addressed, including control of amplicon contamination, specimen treatment to avoid inhibitors, interpretation of positive results when clinical significance is unclear, and cost. Laboratory experience with the Chlamydia Amplicor product (Roche Molecular Systems, Branchburg, NJ) is discussed to illustrate these issues. Commercial kit products using nucleic acid amplification techniques can be introduced into a routine laboratory easily and with a high degree of accuracy.

The accuracy and patient preference for self-collected group B Streptococcus cultures.

OBJECTIVE: Our purpose was to determine the accuracy of and patient attitudes regarding self-collected group B Streptococcus cultures. STUDY DESIGN: Women seen for prenatal care at 24 to 42 weeks' gestation were asked to collect distal vaginal and anal samples for group B Streptococcus. Subsequently, distal vaginal and anal samples were obtained by the nurse. The patients were then asked their preference toward self-sampling. RESULTS: A total of 251 women participated in the study. The incidence of positive group B Streptococcus cultures was 12.7%, 9.6%, 10.0%, and 7.6% for the patient-collected vaginal and anal and nurse-collected vaginal and anal specimens, respectively. The incidence of group B Streptococcus carriage was 17.5% and 13.5% for any positive patient- or provider-collected specimens, respectively, and 19.1% for any positive culture. Single patient-collected vaginal and anal and nurse-collected vaginal and anal samples were insensitive for group B Streptococcus carriage (67%, 50%, 52%, 40%, respectively). The combination of patient-collected samples was more sensitive than nurse-collected samples (sensitivity 91.7% vs 70.8%, p < 0.05). Repeat sampling of the vagina or anal canal did not offer significant additional benefit to a single culture. Overall, patient-collected samples were 98.4% accurate in predicting group B Streptococcus carriage versus 94.4% for nurses. A total of 58% of women preferred obtaining their own specimens, whereas 9.6% found the technique difficult. Ninety percent desired the option of self-sampling in the future. CONCLUSIONS: Single vaginal or anal cultures were insensitive in detecting group B Streptococcus carriage. Combined patient-collected cultures were more sensitive than provider-collected specimens. On the basis of accuracy and patient preference, women should be given the opportunity of combined vaginal-anal self-sampling for group B Streptococcus when indicated.

Analysis of charges associated with diagnosis of nosocomial pneumonia: can routine bronchoscopy be justified?

Many ventilated trauma patients thought to have nosocomial pneumonia have pulmonary contusion or systemic inflammatory response syndrome with tracheobronchial colonization. Fiberoptic bronchoscopy with quantitative culture techniques of protected specimen brush (PSB; threshold 10(3) cfu/mL) or bronchoalveolar lavage (BAL; threshold 10(5) cfu/mL) can potentially eliminate the false positive cultures of the upper airway seen with routine sputum aspirates (RS). However, bronchoscopy is expensive, and routine use may not be cost effective. This prospective study evaluated the patient charges associated with bronchoscopy and quantitative cultures compared with RS for the diagnosis of nosocomial pneumonia. Specimens were obtained by RS, PSB, and BAL from the lower airway in 107 trauma patients (136 sets of triplicate cultures). All patients had clinical evidence suggestive of pneumonia (fever, leukocytosis, purulent sputum, abnormal roentgenographic findings). Typical oral flora were considered contaminants; no gram-negative specimens were excluded. Mean age was 40 years and mean ISS was 29. Seventy-eight percent had blunt injuries, 22% penetrating, and 42% had chest injuries. The incidence of nosocomial pneumonia according to each method was: RS-73%; PSB-34%; BAL-25%. Considering all charges involved (bronchoscopy, equipment, microbiologic analysis, and antibiotics), and based on a 14-day course of ceftazidime and vancomycin, the charges for PSB were 58% of RS, and charges for BAL were 43% of RS. We conclude that the charges associated with bronchoscopy are high, but can be offset by antibiotic savings. Side effects of unnecessary antibiotic therapy would be avoided. Further study is needed to determine the efficacy of PSB or BAL in trauma patients.

Bronchoscopic diagnosis of pneumonia.

Lower respiratory tract infections are characterized by significant morbidity and mortality but also by a relative inability to establish a specific etiologic agent on clinical grounds alone. With the recognized shortcomings of expectorated or aspirated secretions toward establishing an etiologic diagnosis, clinicians have increasingly used bronchoscopy to obtain diagnostic samples. A variety of specimen types may be obtained, including bronchial washes or brushes, protected specimen brushings, bronchoalveolar lavage, and transbronchial biopsies. Bronchoscopy has been applied in three primary clinical settings, including the immunocompromised host, especially human immunodeficiency virus-infected and organ transplant patients; ventilator-associated pneumonia; and severe, nonresolving community- or hospital-acquired pneumonia in nonventilated patients. In each clinical setting, and for each specimen type, specific laboratory protocols are required to provide maximal information. These protocols should provide for the use of a variety of rapid microscopic and quantitative culture techniques and the use of a variety of specific stains and selective culture to detect unusual organism groups.

Significance of serial C-reactive protein responses in neonatal infection and other disorders.

OBJECTIVE: This study was performed to determine prospectively whether, in the presence of proved or presumed bacterial infection, the sensitivity of serum C-reactive protein (CRP) response could be enhanced by serial rather than single determinations. We also sought to assess CRP responses to clinically identified noninfectious disorders. DESIGN: The CRP responses of 491 infants on 691 occasions of suspected infection were assessed. CRP levels were measured initially and twice again at 12-hour intervals (rate immunonephelometry). Assessments also included a blood culture, complete blood cell count, and chest radiograph and culture of spinal fluid when appropriate. CRP responses were correlated with four designated clinical groups: (1) positive blood or cerebrospinal fluid cultures (n = 190); (2) negative blood culture-definite infection (necrotizing enterocolitis stages 2 and 3, pneumonia, subcutaneous abscess) (n = 52); (3) negative blood culture-possible infection (antenatal risk factors, meconium aspiration, positive urine group B streptococcus antigen, necrotizing enterocolitis stage 1, febrile infants) (n = 287); and (4) negative blood culture-no infection (respiratory distress syndrome, transient tachypnea of the newborn, patent ductus arteriosus, tissue trauma) (n = 160). Diagnoses were made before CRP results were known. RESULTS: In all, 187 (27%) of the blood cultures were positive. A single organism was recovered from 174 of these; two organisms from 13. Among the single-organism cultures, 50 (29%) were Gram-negative, 120 (69%) were Gram-positive, and 4 (2%) were budding yeasts. CRP levels were elevated in various groups as follows: in the positive blood culture group (by organism), Gram-negative rods, 92% (46/50); group B streptococcus, 92% (12/13); Staphylococcus aureus, 89% (8/9); group D streptococcus, 71% (10/14); Streptococcus viridans, 60% (6/10); Staphylococcus epidermidis, 55% (40/73). In the negative blood culture-definite infection group, CRP levels were abnormal in 88%; in the negative culture-possible infection group, CRP was elevated in 33%; and in the negative blood culture-no infection group, CRP was elevated in 9%. Serial determinations of CRP resulted in enhanced sensitivity in the positive blood culture group, the negative blood culture-definite infection group, and the negative blood culture-possible infection group. Initial determinations by themselves were inadequately sensitive. Serial determinations did not enhance sensitivity of the negative blood culture-no infection group. High specificity (91%) is suggested by the low incidence of abnormal CRP levels among infants who were not infected. CONCLUSIONS: These data suggest that it would be appropriate to conduct a cautious, controlled trial to assess the safety of discontinuing antibiotic therapy if three serial CRP measurements are normal and if there are no other clinical factors suggestive of infection. The data also indicate the necessity for serial determinations of CRP for optimal sensitivity.

Microbiologic diagnosis of ventilator-associated pneumonia.

Specific etiologic diagnosis in ventilator-associated pneumonia is critical to optimal patient care, and a wide array of microbiologic procedures are available to aid in diagnosis. In bacterial infection, direct stains, particularly the Gram stain, provide rapid presumptive information, and cultures provide definitive identification. Specimen selection is critical; endotracheal or ordinary bronchoscopic aspirates provide nonspecific information, and quantitative analysis of protected specimen brushes or bronchoalveolar lavage provides more accuracy. Specialized procedures for other groups of organisms, such as Chlamydia, Legionella, mycobacteria, fungi, and viruses, also may be indicated in some cases.

Case report: acute postoperative respiratory failure caused by Chlamydia pneumoniae and diagnosed by bronchoalveolar lavage.

Most Chlamydia pneumoniae infections are mild, but 10% develop into pneumonia. C. pneumoniae has been observed in hospital in intubated patients undergoing major surgery or admitted with severe trauma. A patient with squamous cell carcinoma in whom severe pneumonia developed postpneumonectomy and who required mechanical ventilation is presented. The patient was initially treated for nosocomial bacterial pneumonia with the broad spectrum antibiotics ceftazidime, amikacin, and vancomycin. The patient underwent a bronchoalveolar lavage, from which C. pneumoniae was grown. Generally, these patients are a high-risk mortality group. Only after substituting the above antibiotics with doxycycline, to which C. pneumoniae was sensitive, did the pneumonia respond. Whether this was a nosocomial or a community-acquired pneumonia is uncertain.

Protected bronchoalveolar lavage. A new bronchoscopic technique to retrieve uncontaminated distal airway secretions.

We tested the effectiveness of protected bronchoalveolar lavage (PBAL), performed through a protected transbronchoscopic balloon-tipped (PBT) catheter, in collecting distal airway secretions with a minimal degree of contamination. The PBAL had less than or equal to 1% squamous epithelial cells in 91% of specimens and an absence of bacterial growth in 59% of patients without pneumonia. Using a threshold of 10(4) cfu/ml we had one false positive result in 33 patient without pneumonia and one false negative in 13 patients with pneumonia. Quantitative bacterial cultures of the PBAL specimens had a diagnostic sensitivity of 97% and a specificity of 92%, with a positive predictive value of 97% and a negative predictive value of 92%. The diagnostic efficiency was 96%. The presence of intracellular organisms in much greater than or equal to 2% of the recovered alveolar cells (Giemsa stain) was seen in all but two patients with pneumonia (on corticosteroids) and in none of the patients without pneumonia. Gram stains of the PBAL specimens were positive in all but one patient with pneumonia and negative in all but one patient without infection (patient with endobronchial narrowing secondary to neoplasm with false positive cultures). Either the Giemsa or the Gram stain was positive in all patients with pneumonia, allowing early and accurate diagnosis of lower respiratory tract infection before the results of cultures were available. The time off antibiotic therapy before bronchoscopy did not affect the result of PBAL cultures, contrary to what we observed for the protected brush specimen.

Evaluation of two rapid group B streptococcal antigen tests in labor and delivery patients.

Two rapid group B streptococcal antigen tests were compared with nonselective blood agar culture in 1062 unselected patients admitted to labor and delivery. Vaginal specimens taken from each patient on admission were used to perform each of two rapid tests and corresponding cultures. The rapid tests were the Streptex latex agglutination assay and the Equate Strep B test, which uses a solid-phase immunoassay. Overall, 105 patients (9.9%) had at least one positive culture. The sensitivities for the rapid tests were 15.1% for Streptex and 21.5% for Equate. Specificities were 99.3 and 98.7%, respectively. Sensitivity was minimally increased in the setting of ruptured membranes for both tests. Likewise, use of separate swabs for streaking the culture plate and performing the rapid test increased the sensitivity, but this was not significant for either test. In control experiments, the limit of sensitivity of both rapid tests was 5 x 10(6) colony-forming units. We conclude that at present, these tests are not sensitive enough for routine use in this type of clinical setting.

Rapid detection of Pneumocystis carinii in bronchoalveolar lavage samples by using Cellufluor staining.

Cellufluor (Calcofluor white) has been found to be a useful, rapid chemofluorescent stain for detection of Pneumocystis carinii cysts in bronchoalveolar lavage samples. When compared with toluidine blue O and Giemsa stains on 45 specimens (22 positive and 23 negative), the sensitivity and specificity of the Cellufluor stain were 95 and 100%, respectively.

Chlamydia trachomatis infection in pregnancy and effect of treatment on outcome.

The effect of Chlamydia trachomatis on pregnancy outcome and the effect of treatment of positive cervical cultures was studied by culturing 11,544 women for chlamydia at their first prenatal visit. Chlamydia culture was positive in 2433 (21.08%) and prevalence was related to age and race. Of the positive cultures, 1110 were classified as untreated. The untreated group demonstrated a significant increase in the incidence of premature rupture of the membranes and low birth weight and a decrease in survival when compared with either those with positive cultures who received treatment (N = 1323) or those with negative cultures (N = 9111). Screening of populations at high risk of chlamydia is recommended and treatment of chlamydia-positive patients may improve pregnancy outcome.

Treatment of chlamydial infections of the cervix during pregnancy.

Chlamydia trachomatis infections in pregnancy are associated with a high rate of transmission to the newborn and may be associated with poor obstetrical outcome including low birth weight, premature delivery, stillbirth and neonatal death. This prospective study of 99 chlamydia infected women assessed the clinical efficacy of treating chlamydial infections diagnosed at the initial obstetrical visit. Twelve women had concomitant gonococcal and/or urinary tract infections. Seven day regimens of erythromycin 1 gm per day and erythromycin 2 gm per day appear to be equally effective (95.1% and 92.3% respectively) in the treatment of chlamydial infections in pregnancy. Successive therapy did not vary with gestational age when treated. Four of 91 erythromycin treated women discontinued therapy due to gastrointestinal distress. Eight women received sulfisoxazole 4 gm per day and all responded to therapy. Additional controlled studies are needed to determine the most efficacious treatment for chlamydial infections in pregnancy.

Indwelling umbilical arterial catheter: a preferred sampling site for blood culture.

Indwelling umbilical arterial catheter was evaluated prospectively as an alternative site for blood culture sampling. In 282 infants, 318 paired blood cultures were obtained from the peripheral vein and from the indwelling umbilical arterial line. Duration of umbilical catheter placement ranged from 0.5 to 196 hours; in 17% of the infants, catheters were in place for between 24 and 196 hours. In 13 blood culture pairs the same pathogens were found and had been obtained from the peripheral vein and the umbilical arterial line. Two pairs were positive for discrepant organisms. A total of 11 pairs were positive in one site only, with five positive from peripheral vein only and the other six from the umbilical arterial catheter. However, most of these single-site positive blood cultures were apparently true positives based on supporting laboratory data for infection. Contamination rates were 1.3% and 0.9% for peripheral vein and umbilical arterial catheter blood cultures, respectively. Thus, in sick neonates, the indwelling umbilical arterial line was an alternative and perhaps a preferred site for blood culture sampling.

Pneumonia due to Aeromonas hydrophila-complex: epidemiologic, clinical, and microbiologic features.

Review of published data examining the various types of infections produced by strains of the Aeromonas hydrophila-complex demonstrates a paucity of information on lower respiratory tract infections due to this organism. Although it is rarely cited as a cause of pneumonitis, we have been able to collect epidemiologic, clinical, and microbiologic data on eight patients who have had evidence of Aeromonas pneumonia. Interestingly, seven of the eight patients were male, and the average age for the group was 54.3 years. In contrast to reports showing a prevalence of other types of A hydrophila infections during the summer months, five of the pneumonitis cases occurred during late fall and early winter. Infections were both community-acquired and nosocomial. A proven or suspected history of aspiration was present in six patients. Preexisting medical conditions were noted in all patients, the majority having multiple predisposing factors, which included alcohol abuse and alcoholic liver disease, cardiovascular and cerebrovascular disease, and chronic lung disease. Three patients died of their acute pulmonary infection. Based on in vitro antimicrobial susceptibility testing, aminoglycoside therapy would seem appropriate in the treatment of these infections.

A comparison of nonculture-dependent methods for detection of Chlamydia trachomatis infections in pregnant women.

Two nonculture-dependent methods for the detection of Chlamydia trachomatis in endocervical samples from obstetric patients were compared with routine isolation in McCoy cell cultures. When compared with culture, the sensitivities and specificities of the methods were: direct fluorescent antibody staining (MicroTrak [Syva Co.]) 98.1 and 95.4%, and enzyme immunoassay (Chlamydiazyme [Abbott Laboratories]) 96.3 and 92.9%, respectively. In 89% of apparent false-positive direct fluorescent antibody cases and 64% of enzyme immunoassay cases, an additional positive nonculture result was considered to indicate infection missed by culture. Considering these data, revised sensitivities were 84.4% for culture, 95.2% for direct fluorescent antibody, and 95.3% for enzyme immunoassay. Revised specificities were 99.5% for direct fluorescent antibody and 97.3% for enzyme immunoassay. Both nonculture tests appear acceptable for screening high-risk obstetric patients, and may be more sensitive than routine cell culture.

An evaluation of two rapid bacteriuria screening procedures.

Two commercially available rapid bacteriuria screening procedures were evaluated for routine screening for 10(4) or more colony forming units per milliliter of pathogenic bacteria in two female patient populations. In 694 obstetric patients with 56 cases of significant bacteriuria, the sensitivity, specificity, positive predictive, and negative predictive values, respectively, were as follows: for Chemstrip LN, 69.6, 83.4, 26.9, and 96.9%; and for Bac-T-Screen, 96.4, 56.0, 16.1, and 99.4%. In 143 nonpregnant females with 32 cases of significant bacteriuria, these values were: for Chemstrip LN, 71.9, 75.7, 46.0, and 90.3%; and for Bac-T-Screen, 84.4, 65.8, 41.5, and 93.6%. These results indicate that the LN strip did not have acceptable sensitivity in either patient group. The Bac-T-Screen had better sensitivity, particularly for obstetric patients; however, a high false-positive rate and high cost per test may restrict its use in those clinical settings where culture is available and cost-effective.