Emerging pathogens in nosocomial pneumonia

Nasal and perirectal colonization of vancomycin sensitive and resistant enterococci in patients of paediatrics ICU (PICU) of tertiary health care facilities

BACKGROUND

Enterococci normally inhabit the intestinal tract of humans and are also a potential pathogen in causing nosocomial infections. The increase in antibiotic resistance and transfer of antibiotic resistance gene to Staphylococcus aureus (S. aureus) due to co-colonization has increased its importance in research. The aim of the study was to evaluate local epidemiology of nasal and rectal colonization with Enterococcus faecalis (E. faecalis) and Enterococcus faecium (E. faecium) in patients of Paediatrics Intensive Care Unit (PICU) and correlation with clinical and socioeconomic factors.

METHODS

The nasal and perirectal swab samples were collected from 110 patients admitted in PICUs of three tertiary care hospitals of Rawalpindi Medical College, Pakistan. The identification of enterococci was done by biochemical tests and by PCR for ddl, vanA and vanB genes. Antibiotic susceptibility testing was performed by disc diffusion and MICs were determined for vancomycin, tetracycline, ciprofloxacin and oxacillin only.

RESULTS

Out of 220 nasal and perirectal samples, 09 vancomycin-resistant enterococci (VRE) and 76 vancomycin-susceptible enterococci (VSE), consisting of 40 E. faecalis and 45 E. faecium were isolated. PCR successfully identified both species with ddl primers and VRE with vanA primer. With disc diffusion method, all isolates were resistant to most of the antibiotics tested except linezolid, quinupristin/dalfopristin, teicoplanin and vancomycin. VRE showed resistance to teicoplanin and vancomycin both and none was resistant to linezolid and quinupristin/dalfopristin. Generally, E. faecium isolates were more resistant than E. faecalis. MICs of vancomycin for nasal and perirectal VRE were 512 mg/L and 64 to 512 mg/L respectively. VRE were more in patients with prolonged hospitalization, from urban localities and those having pneumonia.

CONCLUSION

Present study reveals high colonization and antibiotic resistance in enterococcal isolates from nasal and perirectal area. Nasal colonization by enterococci in PICU is more alarming as VRE may cause infection and can transfer this resistance gene to other microorganisms like S. aureus.

Prospective, randomized comparison of intravenous and oral ciprofloxacin with intravenous ceftazidime in the treatment of nosocomial pneumonia

OBJECTIVE

To compare the efficacy of intravenous and oral ciprofloxacin and intravenous ceftazidime in the treatment of nosocomial pneumonia.

DESIGN

Randomized, nonblinded, multicentre comparative trial.

SETTING

Seven Canadian university hospitals.

POPULATION

Adult patients with moderate to severe pneumonia developing 72 h or longer after hospitalization.

METHODS

After informed consent was obtained, patients were randomized to receive intravenous ciprofloxacin 300 mg every 12 h or ceftazidime 2 g every 8 h. After three days, patients in the ciprofloxacin arm could be switched to oral ciprofloxacin, 750 mg every 12 h. Concomitant clindamycin was allowed for three days in patients with syndromes consistent with Gram-positive or anaerobic infection. Erythromycin could be used if cultures revealed no pathogen.

RESULTS

A total of 149 patients were enrolled, of whom 124 were eligible for efficacy analysis. Of 119 pathogens identified in 87 patients, 84 were Gram-negative, and 35 Gram-positive. The mean duration of ciprofloxacin therapy was 12.1 days, of which 9.2 days were given intravenously. Ceftazidime was given for a mean of 9.8 days. There was eradication or reduction of pathogens in 75.7% of ciprofloxacin patients and 70.6% of the ceftazidime group. Clinical resolution or improvement occurred in 87.1% of ciprofloxacin recipients and 87.3% of the ceftazidime group. Eight ciprofloxacin and six ceftazidime patients died. Overall outcomes were considered to be successful in 85.2% of ciprofloxacin patients and 87.1% of ceftazidime recipients. Adverse events were mild.

CONCLUSIONS

There were similar efficacy and safety of intravenous and oral ciprofloxacin and intravenous ceftazidime in the treatment of patients with hospital-acquired pneumonia. Physicians were reluctant to use oral therapy in patients.

Clinical practice guidelines for hospital-acquired pneumonia and ventilator-associated pneumonia in adults

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are important causes of morbidity and mortality, with mortality rates approaching 62%. HAP and VAP are the second most common cause of nosocomial infection overall, but are the most common cause documented in the intensive care unit setting. In addition, HAP and VAP produce the highest mortality associated with nosocomial infection. As a result, evidence-based guidelines were prepared detailing the epidemiology, microbial etiology, risk factors and clinical manifestations of HAP and VAP. Furthermore, an approach based on the available data, expert opinion and current practice for the provision of care within the Canadian health care system was used to determine risk stratification schemas to enable appropriate diagnosis, antimicrobial management and nonantimicrobial management of HAP and VAP. Finally, prevention and risk-reduction strategies to reduce the risk of acquiring these infections were collated. Future initiatives to enhance more rapid diagnosis and to effect better treatment for resistant pathogens are necessary to reduce morbidity and improve survival.

Enterococcus pneumonia complicated with empyema and lung abscess in an HIV-positive patient. Case report and review of the literature

This report describes the first case of vancomycin-resistant Enterococcus pneumonia complicated with empyema and lung abscess in an HIV patient and reviews previously published cases of Enterococcus pleuro-pulmonary infection. Our case highlights the rarity of this entity and reviews the risk factors for Enterococcus pleuro-pulmonary infections.

Etiology of Ventilator-Associated Pneumonia

This review focuses on the top ten causes of ventilator-associated pneumonia (VAP), updating an earlier study. These pathogens have specific risk factors, different patterns of clinical resolution, and a wide range of attributable mortality. The discussion herein analyzes these aspects, placing particular emphasis on risk factors, attributable mortality, resistance, and the implications for management.

Expression of type IV pili by Moraxella catarrhalis is essential for natural competence and is affected by iron limitation

Type IV pili, filamentous surface appendages primarily composed of a single protein subunit termed pilin, play a crucial role in the initiation of disease by a wide range of pathogenic bacteria. Although previous electron microscopic studies suggested that pili might be present on the surface of Moraxella catarrhalis isolates, detailed molecular and phenotypic analyses of these structures have not been reported to date. We identified and cloned the M. catarrhalis genes encoding PilA, the major pilin subunit, PilQ, the outer membrane secretin through which the pilus filament is extruded, and PilT, the NTPase that mediates pilin disassembly and retraction. To initiate investigation of the role of this surface organelle in pathogenesis, isogenic pilA, pilT, and pilQ mutants were constructed in M. catarrhalis strain 7169. Comparative analyses of the wild-type 7169 strain and three isogenic pil mutants demonstrated that M. catarrhalis expresses type IV pili that are essential for natural genetic transformation. Our studies suggest type IV pilus production by M. catarrhalis is constitutive and ubiquitous, although pilin expression was demonstrated to be iron responsive and Fur regulated. These data indicate that additional studies aimed at elucidating the prevalence and role of type IV pili in the pathogenesis and host response to M. catarrhalis infections are warranted.

Occurrence of ventilator-associated pneumonia in mechanically ventilated pediatric intensive care patients during stress ulcer prophylaxis with sucralfate, ranitidine, and omeprazole

PURPOSE

The purpose of the study was to evaluate the effects of sucralfate, ranitidine, and omeprazole use on incidence of ventilatory-associated pneumonia (VAP) and mortality in ventilated pediatric critical care patients.

MATERIALS AND METHODS

This prospective study was conducted at the pediatric intensive care unit (PICU) between August 2000 and February 2002. A total of 160 patients who needed mechanical ventilation were randomized into 4 groups according to the computer-generated random number table: group (S), (n = 38) received sucralfate suspension 60 mg/kg/d in 4 doses via the nasogastric tube that was flushed with 10 mL of sterile water; group (R), (n = 42) received ranitidine 2 mg/kg/d intravenously in 4 doses; group (O), (n = 38) received omeprazole 1 mg/kg/d intravenously in 2 doses; and group (P), (n = 42) did not receive any medication for stress ulcer prophylaxis. Treatment was begun within 6 hours of PICU admission.

RESULTS

Seventy patients (44%) developed VAP. VAP rate was 42% (16 of 38) in the sucralfate group, 48% (20 of 42) in the ranitidine group, 45% (17 of 38) in the omeprazole group, and 41% (17 of 42) in the nontreated group. Overall mortality rate was 22% (35 of 160); it was 21% (8 of 38) in the sucralfate group, 23% (10 of 42) in the ranitidine group, 21% (8 of 38) in the omeprazole group, and 21% (9 of 42) in the nontreated group. Our results did not show any difference in the incidence of VAP and mortality in mechanically ventilated PICU patients treated with ranitidine, omeprazole, or sucralfate, or nontreated subjects (P =.963, confidence interval [CI] = 0.958-0.968; P =.988, CI = 0.985-0.991, respectively). Nine patients (5.6%) had macroscopic bleeding. There was no statistically significant difference in macroscopic bleeding between groups.

CONCLUSIONS

Our results did not show any difference in the incidence of VAP, macroscopic stress ulcer bleeding, and mortality in the mechanically ventilated PICU patients treated with ranitidine, omeprazole, or sucralfate, or nontreated subjects. None of the treatment regimens increased VAP compared with the nontreated group. Because there is insufficient data about stress ulcer prophylaxis and VAP in the pediatric age group, more studies with larger numbers of patients are needed.

Moraxella catarrhalis: from emerging to established pathogen

Moraxella catarrhalis (formerly known as Branhamella catarrhalis) has emerged as a significant bacterial pathogen of humans over the past two decades. During this period, microbiological and molecular diagnostic techniques have been developed and improved for M. catarrhalis, allowing the adequate determination and taxonomic positioning of this pathogen. Over the same period, studies have revealed its involvement in respiratory (e.g., sinusitis, otitis media, bronchitis, and pneumonia) and ocular infections in children and in laryngitis, bronchitis, and pneumonia in adults. The development of (molecular) epidemiological tools has enabled the national and international distribution of M. catarrhalis strains to be established, and has allowed the monitoring of nosocomial infections and the dynamics of carriage. Indeed, such monitoring has revealed an increasing number of B-lactamase-positive M. catarrhalis isolates (now well above 90%), underscoring the pathogenic potential of this organism. Although a number of putative M. catarrhalis virulence factors have been identified and described in detail, their relationship to actual bacterial adhesion, invasion, complement resistance, etc. (and ultimately their role in infection and immunity), has been established in a only few cases. In the past 10 years, various animal models for the study of M. catarrhalis pathogenicity have been described, although not all of these models are equally suitable for the study of human infection. Techniques involving the molecular manipulation of M. catarrhalis genes and antigens are also advancing our knowledge of the host response to and pathogenesis of this bacterial species in humans, as well as providing insights into possible vaccine candidates. This review aims to outline our current knowledge of M. catarrhalis, an organism that has evolved from an emerging to a well-established human pathogen.

Prevalence and risk factors for nosocomial lower respiratory tract infections in German hospitals

The prevalence and risk factors for nosocomial lower respiratory tract infections (LRTI) in Germany were determined as part of a national survey on nosocomial infections. The study included 14,966 patients in 72 representatively selected hospitals with departments of general medicine, surgery, obstetrics, gynecology, and intensive care units (ICU). Surveillance was carried out by four previously validated medical doctors who strictly applied the CDC-criteria for diagnosis of nosocomial infections. The overall prevalence of hospital-acquired LRTI was 0.72% with the highest rate in hospitals with more than 600 beds (1.08%) and among the patients on intensive care units (9.00%). Ventilator-associated pneumonia rates were highest in patients on ICUs (13.27). Polytrauma, impaired consciousness, chronic airway disease, prior surgery, and cardiovascular disease were significantly related to the occurrence of nosocomial LRTI. P. aeruginosa was the predominant organism causing nosocomial LRTI. Nosocomial LRTI remain a problem mainly on ICUs. Patients at risk should be monitored with extra care.

Risk factors for infection by Acinetobacter baumannii in intubated patients with nosocomial pneumonia

STUDY OBJECTIVE

To investigate the epidemiology of infection by Acinetobacter baumannii in patients with ventilator-associated pneumonia (VAP).

DESIGN

Prospective clinical study.

SETTING

Three medical-surgical ICUs in teaching hospitals.

PATIENTS

We followed up 707 mechanically ventilated patients and 148 episodes of VAP with etiologic diagnosis.

RESULTS

A baumannii was isolated in 12 (8.1%) episodes in 148 patients. Five of these episodes were directly responsible for death. Using logistic regression analysis, the risk of VAP due to A baumannii was found to be high in patients with neurosurgery (odds ratio [OR]=10.03; 95% confidence interval [CI]=1.55 to 64.90), ARDS (OR=9.73; 95% CI=1.60 to 59.24), head trauma (OR=5.17; 95% CI=0.88 to 30.34), and large-volume pulmonary aspiration (OR=2.90; 95% CI=0.80 to 10.53).

CONCLUSIONS

Intubated patients who develop pneumonia and have any of the above factors are at an increased risk of Acinetobacter infection.

Colonization and infection with Enterococcus faecalis in intensive care units: the role of antimicrobial agents

We studied the influences of antimicrobial agents on the colonization of the respiratory tract and infection with Enterococcus faecalis in intensive care unit (ICU) patients receiving mechanical respiration for at least 3 days. In a matched-cohort analysis, patients receiving topical antimicrobial prophylaxis (TAP) of the oropharynx and stomach with antimicrobial agents not treating E. faecalis were compared with patients not receiving TAP. Patients were matched with controls on the basis of their duration in the ICU, their use of systemic antibiotics treating and not treating E. faecalis, the administration of TAP, their APACHE II score, and surgical procedures they had undergone. In all, 276 patients were analyzed. The colonization of the oropharynx and/or trachea by E. faecalis at admission was demonstrated for 43 patients (16%). Twenty patients (9%) acquired tracheal colonization and 91 patients (40%) acquired oropharyngeal colonization with E. faecalis. In the matched-cohort analysis, 43 patients receiving TAP were matched in two controls each. TAP patients more frequently acquired tracheal colonization (15 of 43 versus 2 of 86 patients, P < 0.00001) and infections with E. faecalis (6 of 43 versus 1 of 86 patients, P < 0.01). The use of topical antibiotics and treating E. faecalis increased the risk for colonization and infection with E. faecalis.

Risk factors for adverse outcome in persons with pneumococcal pneumonia

OBJECTIVE

To identify risk factors for death and respiratory failure in persons with penicillin-sensitive pneumococcal bacteremia and pneumonia from data available at initial clinical evaluation.

DESIGN

Retrospective chart review of persons with pneumococcal bacteremia and pneumonia.

SETTING

Tertiary care medical center (University of California Davis Medical Center, Sacramento).

PATIENTS

One hundred two consecutive adults admitted to the hospital for treatment of pneumococcal pneumonia with bacteremia.

RESULTS

Of 102 persons, 25 (25%; 95% confidence interval [CI], 17 to 34%) died and 17 (16%; 95% CI, 10 to 25%) survived mechanical ventilation for respiratory failure. In univariate analyses, persons with preexisting lung disease (relative risk [RR], 2.0; 95% CI, 1.3 to 3.1), initial body temperature < 38 degrees C (RR, 2.1; 95% CI, 1.3 to 3.6), or nosocomial infections (RR, 2.5; 95% CI, 1.8 to 3.6) or who were > or = 48 years old (RR, 2.7; 95% CI, 1.5 to 4.8) were at greater risk for adverse outcomes than persons without these risk factors. Of 25 persons without these risk factors, only one (4%; 95% CI, 0 to 20%) died, and the remaining 24 persons did not require intensive care. Using these risk factors in a multivariate logistic model, death or respiratory failure would have been predicted in 67% of persons and better outcome predicted in 83% of the persons. In multivariate analysis, nosocomial infection was the greatest risk factor (adjusted odds ratio, 17.3; 95% CI, 3.1 to 98).

CONCLUSIONS

Risk factors identified at hospital admission can predict the outcome in persons with pneumococcal pneumonia and bacteremia. Identifying these factors may allow earlier use of intensive care or more aggressive treatment. Independent of age, nosocomially acquired infections were the greatest risk factor for death or respiratory failure.

Risk factors for infection by Pseudomonas aeruginosa in patients with ventilator-associated pneumonia

OBJECTIVE

to investigate the epidemiology of infection by Pseudomonas aeruginosa in patients with ventilator-associated pneumonia (VAP).

DESIGN

prospective clinical study.

SETTING

a medical-surgical ICU in a university hospital.

PATIENTS

we followed-up 568 mechanically ventilated patients and 83 episodes of VAP with etiologic diagnosis in 72 patients were retained for analysis.

RESULTS

Ps. aeruginosa was isolated in 22 (26.5%) episodes in 18 patients. Of these episodes 7 were directly responsible for death. Using logistic regression analysis, the risk of VAP due to Ps. aeruginosa was increased in patients with chronic obstructive pulmonary disease (relative risk (RR) = 29.9, 95% confidence interval (CI) = 4.86-184.53), a mechanical ventilation period longer than 8 days (RR = 8.1, 95% CI = 1.01-65.40) and prior use of antibiotics (RR = 5.5, 95% CI = 0.88-35.01).

CONCLUSIONS

patients with VAP and these factors have a greater risk of infection by Ps. aeruginosa and empirical therapy for these episodes should include anti-pseudomonal activity until etiologic diagnosis is established.

The role of salivary function on oropharyngeal colonization

Aspiration of oropharyngeal flora is the most common route of acquiring Gram-negative pneumonia, a major nosocomial infection. Epidemiologic studies indicate that the elderly are at increased risk for developing these life-threatening pneumonias. The primary objective of this study was to determine the effects of salivary oral defenses against Gram-negative colonization. The study population consisted of 41 male outpatients, age 70 and older, seen at the Denver VAMC. The group included subjects with both diminished and normal salivary flow. Each subject answered a questionnaire regarding overall health, medication use, and symptoms of salivary dysfunction. We then collected whole saliva, unstimulated and stimulated parotid saliva, and performed a throat swab on each patient. For each throat culture, analysis was done to identify Gram-negative bacteria. Flow rates between colonized (n = 6) and noncolonized subjects (n = 34) were compared. While there were no significant differences in the flow rates between the two groups, a trend was noticed in that flow rates were lower for all three flow measures in the colonized group (whole, 22% decrease; unstimulated, 22% decrease; and stimulated, 28% decrease). These preliminary findings suggest that subjects with diminished salivary flow may possibly be at increased risk for oropharyngeal Gram-negative colonization. Research on the role that saliva plays in oropharyngeal bacterial colonization is continuing.

Systemic antibiotic treatment of nosocomial pneumonia

Nosocomial pneumonia continues to represent a significant cause of morbidity and mortality in hospitalized patients. Bacteria are responsible for greater than 90% of the pneumonias, the most common isolates being aerobic Gram-negative bacilli and S. aureus. Cornerstones of treatment are intravenous antibiotics and supportive care. In the individual case the true etiology is usually unknown; therefore empiric broad spectrum treatment is commonly used based on the prevalence of local pathogens, their antibiotic sensitivity pattern and on host factors. Combination antibiotic regimens, including beta-lactams and aminoglycosides, are considered as standard therapy and are associated with clinical success rates of greater than 80%. Monotherapy with broad spectrum antibiotics, such as third generation cephalosporins, imipenem and fluoroquinolones, can be considered as equally effective in non-neutropenic patients and in the absence of P. aeruginosa infection. More active and less toxic antibiotics are still needed for problematic pathogens such as methicillin-resistant S. aureus strains, multiresistant Enterobacteriaceae and Pseudomonas species. Because further improvement in morbidity and mortality may be limited with antibiotics alone, new emphasis should be placed on prevention of infection and the use of immunotherapy.

Drug treatment of pneumonia in the hospital. What are the choices?

Mortality and morbidity of nosocomial pneumonia remain high. Successful treatment of pulmonary infections depends on several factors including type of infection, offending pathogen, status of host defences, and adequate choice of antibiotic therapy. The physician's decision should aim at achieving antibiotic concentrations beyond the MIC at the site of infection. Gram-negative bacilli, notably Pseudomonos aeruginosa, Klebsiella pneumoniae and Escherichia coli, remain the most frequent agents in nosocomial pneumonia. Staphylococcus aureus and Streptococcus pneumoniae predominate among the Gram-positive cocci. Pneumocystis carinii predominates in immunocompromised patients. Protected sample bronchoscopy associated with quantitative cultures of samples, and quantification of intracellular microorganisms in cells recovered by broncho-alveolar lavage are two promising procedures which might replace previous, more aggressive methods. Penetration of antibiotics into lung tissue depends on physicochemical properties of the drug and the degree of inflammation of lung tissue. Quinolones, macrolides, tetracyclines and trimethoprim penetrate well into bronchial secretions. Penetration is moderate to low for aminoglycosides and beta-lactams. Fluoroquinolones and new beta-lactam agents, including third-generation cephalosporins imipenem, aztreonam and ticarcillin-clavulanate, showed comparative clinical efficacy in treatment of nosocomial pneumonia, with an efficacy rate close to 80%. Aminoglycosides should not be used alone. Combination therapy reduces but does not eliminate the risk of selection of Gram-negative resistant mutants. It should not be used routinely except for P. aeruginosa, Enterobacter cloacae and Serratia marcescens infections.

Empiric therapy of severe infections in adults

The third-generation cephalosporins are useful for empiric therapy of most of the severe infections in adults as a result of their broad spectrum of antimicrobial activity (particularly against clinically important gram-negative bacteria), good tissue penetration, and lack of serious adverse effects. This review examines their use in respiratory tract infections, bacterial meningitis, skin-structure infections, and urinary tract infections in adult patients. Penicillin G remains the optimal therapy for severe community-acquired pneumonia, since Streptococcus pneumoniae still accounts for the majority of cases. However, for empiric treatment of nosocomial pneumonia, therapy must ensure coverage both of aerobic gram-negative bacilli and Staphylococcus aureus. The choice of empiric antibiotic therapy in the treatment of urinary tract infections depends on the pattern of resistance in the patient's environment. At present, the treatment of bacterial meningitis in otherwise healthy adults does not constitute a major problem provided that penicillin resistance among pneumococci and meningococci (responsible for at least 80 percent of cases) does not become a clinical problem. However, in meningitis in which gram-negative bacilli are suspected and where specific problems include antibiotic resistance among these organisms and the inadequate penetration of many antibiotics into the cerebrospinal fluid, third-generation cephalosporins are the drugs of choice, and they have markedly improved the clinical outcome. Most skin-structure infections are due to S. aureus and are best treated by an anti-staphylococcal penicillin or an older cephalosporin. Nevertheless, the third-generation cephalosporins have proved to be highly effective agents for infections of skin and soft-tissue infections associated with both gram-positive and gram-negative pathogens in patients at risk from these organisms or in the elderly.