Nosocomial pneumonia in the intensive care unit: mechanisms and significance

Proton pump inhibitor medication is associated with colonisation of gut flora in the oropharynx

BACKGROUND

The normal body exists in mutualistic balance with a large range of microbiota. The primary goal of this study was to establish whether there is an imbalance in the oropharyngeal flora early after hospital or ICU admittance, and whether flora differs between control, ward and critically ill patients. The secondary goal was to explore whether there are patient characteristics that can be associated with a disturbed oropharyngeal flora.

METHODS

Oropharyngeal cultures were obtained from three different study groups: (1) controls from the community, (2) ward patients and (3) critically ill patients, the two latter within 24 h after admittance.

RESULTS

Cultures were obtained from 487 individuals: 77 controls, 193 ward patients and 217 critically ill patients. Abnormal pharyngeal flora was more frequent in critically ill and ward patients compared with controls (62.2% and 10.4% vs. 1.3%, P < 0.001 and P = 0.010, respectively). Colonisation of gut flora in the oropharynx was more frequent in critically ill patients compared with ward patients or controls (26.3% vs. 4.7% and 1.3%, P < 0.001 and P < 0.001, respectively). Proton pump inhibitor medication was the strongest independent factor associated with the presence of gut flora in the oropharynx in both ward and critically ill patients (P = 0.030 and P = 0.044, respectively).

CONCLUSION

This study indicates that abnormal oropharyngeal flora is an early and frequent event in hospitalised patients and more so in the critically ill, compared to controls. Proton pump inhibitor medication is associated with colonisation of gut flora in the oropharynx.

A Stenotrophomonas maltophilia Strain Evades a Major Caenorhabditis elegans Defense Pathway

Stenotrophomonas maltophilia is a ubiquitous bacterium and an emerging nosocomial pathogen. This bacterium is resistant to many antibiotics, associated with a number of infections, and a significant health risk, especially for immunocompromised patients. Given that Caenorhabditis elegans shares many conserved genetic pathways and pathway components with higher organisms, the study of its interaction with bacterial pathogens has biomedical implications. S. maltophilia has been isolated in association with nematodes from grassland soils, and it is likely that C. elegans encounters this bacterium in nature. We found that a local S. maltophilia isolate, JCMS, is more virulent than the other S. maltophilia isolates (R551-3 and K279a) tested. JCMS virulence correlates with intestinal distension and bacterial accumulation and requires the bacteria to be alive. Many of the conserved innate immune pathways that serve to protect C. elegans from various pathogenic bacteria also play a role in combating S. maltophilia JCMS. However, S. maltophilia JCMS is virulent to normally pathogen-resistant DAF-2/16 insulin-like signaling pathway mutants. Furthermore, several insulin-like signaling effector genes were not significantly differentially expressed between S. maltophilia JCMS and avirulent bacteria (Escherichia coli OP50). Taken together, these findings suggest that S. maltophilia JCMS evades the pathogen resistance conferred by the loss of DAF-2/16 pathway components. In summary, we have discovered a novel host-pathogen interaction between C. elegans and S. maltophilia and established a new animal model with which to study the mode of action of this emerging nosocomial pathogen.

Nonfermenting Gram-negative Bacilli other than Pseudomonas aeruginosa and Acinetobacter Spp. Causing Respiratory Tract Infections in a Tertiary Care Center

Background:

Nonfermenting gram-negative bacilli have emerged as important healthcare-associated pathogens. It is important to correctly identify all clinically significant nonfermenting gram-negative bacilli considering the intrinsic multidrug resistance exhibited by these bacteria.

Materials and Methods:

A retrospective study was undertaken to identify the various nonfermenting gram-negative bacilli other than Pseudomonas aeruginosa and Acinetobacter spp. isolated from respiratory samples (n = 9363), to understand their clinical relevance and to analyze their antibiotic susceptibility pattern.

Results:

Nonfermenting gram-negative bacilli were isolated from 830 (16.4%) samples showing significant growth. Thirty-three (4%) isolates constituted nonfermenting gram-negative bacilli other than P. aeruginosa and Acinetobacter spp. Stenotrophomonas maltophilia (15, 45.5%) was the most common isolate followed by Burkholderia cepacia (4, 12.1%), Sphingomonas paucimobilis (3, 9.1%), and Achromobacter xylosoxidans (3, 9.1%). On the basis of clinicomicrobiological correlation, pathogenicity was observed in 69.7% (n = 23) isolates. Timely and correct treatment resulted in clinical improvement in 87.9% cases.

Conclusion:

Any nonfermenting gram-negative bacilli isolated from respiratory tract infection should not be ignored as mere contaminant, but correlated clinically for its pathogenic potential and identified using standard methods so as to institute appropriate and timely antibiotic coverage.

Do cultures contribute to optimisation of antibiotic therapy in the intensive care unit?

Obtaining diagnostic microbiological cultures before initiating empirical antimicrobial therapy is part of the diagnostic work-up of intensive care patients with a clinical suspicion of infection. However, it is unknown to what extent these cultures provide a microbiological cause of infection and to what extent antimicrobial therapy is influenced. During a 6-month period, all episodes of suspected clinical infection were analysed and categorised as non-microbiologically proven infection (non-MPI) or MPI. Effects of culture results on antibiotic therapy were analysed for episodes of respiratory tract infection. Invasive diagnostic techniques were not routinely used for diagnosis of respiratory tract infections. Among 212 patients admitted, 147 episodes of clinical suspicion of infection were recorded (104 for respiratory tract infection) and 1147 microbiological cultures were obtained (0.64 culture per patient day). Antibiotics were administered on 1111 (62%) of 1803 patients days. Of the respiratory tract infections, 571 cultures resulted in 49 (47%) MPI. Cover with empirical antibiotics was inappropriate in 7 of 104 cases (8%) of respiratory infections. In 12 cases (11.5%) empirical therapy could have been changed based on culture results. Negative cultures were never followed by cessation of therapy, but the duration of treatment was significantly shorter for non-MPI. Forty-seven percent of respiratory tract infections were microbiologically confirmed and, based on culture results, empirical antimicrobial therapy could have been influenced in 11.5% of cases of respiratory tract infections. These findings provide aspects to evaluate and improve the diagnostic work-up of infections in the ICU.

Antibiotic Resistance of Bacterial Ventilator-Associated Pneumonia in Surgical Intensive Care Units

Ventilator-associated pneumonia (VAP) is the most common infection in intensive care units. It is caused by prolonged hospitalization and results in high mortality rates. This retrospective clinical study, of 140 patients in a surgical intensive care unit, aimed to identify the bacterial agents responsible for VAP infection, and determine antibiotic resistance rates in VAP. Antibiotic sensitivity was evaluated by culturing and testing tracheal aspirates from patients with clinical and radiological findings of VAP. The bacteria isolated most frequently were Pseudomonas aeruginosa (33.9%), Staphylococcus aureus (30.0%), Acinetobacter baumannii (26.1%), and Enterobacter species (4.3%). A. baumannii was more prevalent than in previous years. The results of antibiotic sensitivity testing suggested sulbactam/cefoperazone as the most appropriate drug for treating these patients. We suggest, however, that when staphylococcal pneumonia is suspected, a glycopeptide (vancomycin or teicoplanin) or combined trimethoprimsulfamethoxazole is used as first-line therapy until sensitivity results are obtained. In conclusion, development of antibiotic policies for individual hospitals can reduce high antibiotic resistance rates due to VAP.

Staphylococcus aureus rectal carriage and its association with infections in patients in a surgical intensive care unit and a liver transplant unit

BACKGROUND

The role of rectal carriage of Staphylococcus aureus as a risk factor for nosocomial S. aureus infections in critically ill patients has not been fully discerned.

METHODS

Nasal and rectal swabs for S. aureus were obtained on admission and weekly thereafter until discharge or death from 204 consecutive patients admitted to the surgical intensive care unit and liver transplant unit

RESULTS

Overall, 49.5% (101 of 204) of the patients never harbored S. aureus, 21.6% (44 of 204) were nasal carriers only, 3.4% (7 of 204) were rectal carriers only, and 25.5% (52 of 204) were both nasal and rectal carriers. Infections due to S. aureus developed in 15.7% (32 of 204) of the patients; these included 3% (3 of 101) of the non-carriers, 18.2% (8 of 44) of the nasal carriers only, 0% (0 of 7) of the rectal carriers only, and 40.4% (21 of 52) of the patients who were both nasal and rectal carriers (P - .001). Patients with both rectal and nasal carriage were significantly more likely to develop S. aureus infection than were those with nasal carriage only (odds ratio, 3.9; 95% confidence interval, 1.18 to 7.85; P= .025). By pulsed-field gel electrophoresis, the infecting rectal and nasal isolates were clonally identical in 82% (14 of 17) of the patients with S. aureus infections.

CONCLUSIONS

Rectal carriage represents an underappreciated reservoir for S. aureus in patients in the intensive care unit and liver transplant recipients. Rectal plus nasal carriage may portend a greater risk for S. aureus infections in these patients than currently realized.

Nosocomial infections

Nosocomial infections and antimicrobial resistance are topics that have been intensely studied in human medicine because of their significant impact on human health. In recent years, concerns have been raised that the use of antibiotics in veterinary medicine, animal husbandry, and agriculture may be contributing to the development of resistance in common bacterial species affecting human beings. Although there is inadequate proof at this time that the resistance is transmitted from animals to people, if antibiotics continue to be used indiscriminately in veterinary medicine, veterinarians may find themselves facing regulations restricting the use of some antibiotics. Nosocomial infections have been reported in veterinary medicine and are likely to increase in prevalence with the increase in intensive care practices in many hospitals. Prolonged hospitalization and the use of invasive devices and procedures increase the risk of nosocomial disease. As in human medicine, organisms isolated in the nosocomial infections reported in veterinary patients have an increasingly broad spectrum of antimicrobial resistance. Despite these findings, the use of empiric and prophylactic antibiotic therapy is still widespread in veterinary medicine. Nosocomial infections and antimicrobial resistance may have a serious impact on the future of [table: see text] veterinary medicine, because the cost and ability to treat our patients may be affected by the loss of access to or effectiveness of antimicrobial drugs. Despite the millions of dollars spent on research to reduce the incidence of nosocomial infections in human patients, the strategies that have consistently proven successful are simple and inexpensive to implement. The most important factor in preventing nosocomial infections is improving the hygiene practices of health care providers. Hand-washing or the use of disposable gloves can dramatically reduce the transmission of bacteria between patients. Aseptic technique should be used in the placement and management of all invasive devices. All staff members should be educated on the risks and symptoms associated with nosocomial infections so that cases can be detected early and treated appropriately. We in the veterinary profession have the opportunity to learn from the experiences of the human medical profession and can take steps to prevent the escalation of nosocomial infections and their impact on our profession.

Prevalence of lower respiratory tract infections in hospitalized patients in the United Kingdom and Eire--results from the Second National Prevalence Survey

During 1993 and 1994, the Hospital Infection Society conducted its Second National Prevalence Survey of infections in patients in British hospitals. The prevalence rates for hospital-acquired (HA) and community-acquired (CA), lower respiratory tract infections (LRTIs) were 2.4% and 6.1%, respectively; this shows an increase over that reported in the First National Prevalence Study. The prevalence rate of HA infections for ventilated patients was 18.6%. The prevalence was greater in males, odds ratio (OR, 95% CI) for HA-LRTIs (1.4, 1.1-1.6) and CA-LRTIs (1.2, 1.1-1.3) than in females. In the case of both HA-LRTIs and CA-LRTIs, there was an increase in prevalence in patients with age >75 years, (HA-LRTIs 1.7, 1.3-2.2; CA-LRTIs 1.7, 1.0-2.7). Results of multivariable logistic regression analysis showed an increased risk of HA-LRTIs in patients who had a nasogastric tube (3.6, 2.3-3.6), were ventilated (2.3, 1.6-3.2), trauma patients (2.2, 1.5-3.0), chronic obstructive airway disease (COAD), (1.9, 1.5-2.3), a tracheostomy (1.9, 1.3-2.7), prior blood transfusion (1.5, 1.2-1.8), smokers (1.4, 1.1-1.6) or on systemic corticosteroid therapy (OR 1.3, 1.1-1.6). Community-acquired LRTIs were positively associated with cystic fibrosis (33.7, 19.1-59.3), HIV (9.8, 6.5-14.8), COAD (4.8, 3.8-4.8), systemic corticosteroid therapy (2.5, 2.2-2.8), tracheostomy (1.8, 1.1-2.9), males (1.2, 1.1-1.3) and smoking (1.2, 1.1-1.4).

Implications of oral infections on systemic diseases in the institutionalized elderly with a special focus on pneumonia

Systemic infection in the elderly patient living in a chronic care setting presents a significant burden to the health care system. The extent to which oral organisms cause systemic infections through hematogenous dissemination in the institutionalized elderly is still unknown. A more likely and common route of systemic infection by oral microorganisms is through aspiration of oropharyngeal fluids containing oral pathogenic microorganisms, which colonize the lower respiratory tract and cause pneumonia. Respiratory pathogens emerge in the dental plaque of elderly patients with very poor oral hygiene and severe periodontal disease. In the chronic care setting, aspiration of oropharyngeal fluids contaminated with these bacteria occurs in patients with diminished host defenses, resulting in bacterial pneumonia. This is also a problem in intensive care units in the hospital setting. In one study, pre-rinsing with a 0.12% chlorhexidine gluconate mouthwash significantly lowered the mortality rate from postsurgical pneumonia in patients undergoing open heart surgery. Selective digestive decontamination, a technique involving the topical application of antimicrobials to reduce the risk of colonization of the respiratory tract, has been used to reduce the incidence of nosocomial pneumonia in the acute care setting of hospitals. This technique has not been employed in the nursing home setting. Whether improving oral hygiene would also lower the risk in either of these settings has not been studied. A number of obstacles must be overcome in designing studies to investigate the relationship between oral infections and lung infections in the institutionalized elderly. Ethical issues must be addressed, and full collaboration of the medical team is required. Future studies should establish whether reducing the risk for pneumonia in the institutionalized elderly is possible through improved oral health.

Microbiological and clinical aspects of infection associated with Stenotrophomonas maltophilia

The gram-negative bacterium Stenotrophomonas maltophilia is increasingly recognized as an important cause of nosocomial infection. Infection occurs principally, but not exclusively, in debilitated and immunosuppressed individuals. Management of S. maltophilia-associated infection is problematic because many strains of the bacterium manifest resistance to multiple antibiotics. These difficulties are compounded by methodological problems in in vitro susceptibility testing for which there are, as yet, no formal guidelines. Despite its acknowledged importance as a nosocomial pathogen, little is known of the epidemiology of S. maltophilia, and although it is considered an environmental bacterium, its sources and reservoirs are often not readily apparent. Molecular typing systems may contribute to our knowledge of the epidemiology of S. maltophilia infection, thus allowing the development of strategies to interrupt the transmission of the bacterium in the hospital setting. Even less is known of pathogenic mechanisms and putative virulence factors involved in the natural history of S. maltophilia infection and this, coupled with difficulties in distinguishing colonization from true infection, has fostered the view that the bacterium is essentially nonpathogenic. This article aims to review the current taxonomic status of S. maltophilia, and it discusses the laboratory identification of the bacterium. The epidemiology of the organism is considered with particular reference to nosocomial outbreaks, several of which have been investigated by molecular typing techniques. Risk factors for acquisition of the bacterium are also reviewed, and the ever-expanding spectrum of clinical syndromes associated with S. maltophilia is surveyed. Antimicrobial resistance mechanisms, pitfalls in in vitro susceptibility testing, and therapy of S. maltophilia infections are also discussed.

Bacterial keratitis in the critically ill

BACKGROUND

In the 4 year period (1988-91 there were nine cases of bacterial keratitis in five critically ill patients on an intensive care unit ('unit A'), all except one due to Pseudomonas aeruginosa. Many of these patients had serious ocular complications requiring surgery and all surviving patients were left with significant visual deficits. One further case of keratitis due to P aeruginosa occurred on unit A in April 1993. The problem of keratitis in ventilated patients is not unique to this unit as a further four cases in three patients from additional units in this area have been treated.

METHODS

Predisposing factors in unit A were established through subsequent investigations. It was found, in particular, that all the ocular infections were preceded by colonisation of the respiratory tract with the pathogenic organism. Recommendations concerning eye care and tracheal suctioning were adopted by unit A in 1991.

RESULTS

In the subsequent 4 years (1991-5), the frequency of isolation of pseudomonas from the respiratory tract per patient treated in unit A remained relatively high at 3.8% (153/4032). However, the conjunctival pseudomonas isolation rate has decreased significantly (p < 0.001) from 0.8% (19/2430) to 0.05% (2/4032).

CONCLUSIONS

Ventilated patients may be at risk from inoculation of pathogens into the eyes. The principal risk factor for bacterial keratitis in this series was corneal exposure secondary to conjunctival chemosis or lid damage. The adoption of simple preventative measures on unit A had a significant impact on the incidence of eye infections due to pseudomonas, despite the high proportion of patients whose respiratory tracts were colonised with the same organism. There is a need for additional research into the most effective method of eye care for ventilated patients in order to reduce the frequency of this avoidable condition.

An analysis of two prevalence surveys of nosocomial infection in German intensive care units

In 1995, the results of two extensive prevalence studies on hospital-acquired infections were published. Both studies included a prevalence component for German intensive care units (ICUs), but provided very different infection rates. A comparison of the methods used revealed that the data from the ICUs included in the German section of EPIC (European Prevalence of Infection in Intensive Care), reflected the situation in the ICUs of large hospitals. The situation in ICUs with fewer than 600 beds was quite different, and led to the lower overall rate of infection as seen in the NIDEP (Nosocomial Infections in Germany-Surveillance and Prevention) study. Additionally, the NIDEP data permitted the calculation of device-associated, device-day, infection rates for urinary tract infections, pneumonia and bacteraemia. The differences between the ICUs in the two hospital groups were mainly due to a lower use of patient devices with regard to urinary catheters, central venous lines and respiratory ventilators.

Ventilator-associated pneumonia due to Pseudomonas aeruginosa

OBJECTIVE

Ventilator-associated pneumonia (VAP) caused by Pseudomonas aeruginosa has been associated with higher case fatality rates than VAP caused by other bacterial etiologies. The causes of this excess mortality are unclear.

DESIGN

Retrospective review of 38 consecutive ventilated patients with Pseudomonas pneumonia, documented by highly reliable methods. Charts of five additional patients were unavailable for review.

SETTING

Medical ICUs of a university-affiliated Veterans Affairs Medical Center and a university-affiliated municipal hospital.

MEASUREMENTS

Prospectively collected hospital admission acute physiologic and chronic health examination (APACHE) II scores and cause of ICU admission. Retrospectively calculated organ failure and APACHE scores, VAP score. Clinical and microbiologic variables. Antibiotic treatment and outcome. Direct cause of death by standard definitions.

RESULTS

Overall mortality was 69% (26/38), significantly higher than the APACHE II predicted mortality of 42.6% (p=0.037). At least 38% (10/26) of deaths were directly attributable to Pseudomonas VAP. Multivariate analysis of factors associated with death found infectious cause for ICU admission (odds ratio [OR]=8.67; 95% confidence interval [CI], 0.86 to 85.94) and number of organ dysfunctions on the day of diagnosis (OR=1.73, 95% CI, 1.02 to 2.92) were significant. Septic shock from Pseudomonas VAP, septic shock from subsequent infection, and multiple organ dysfunction syndrome were the most common immediate causes of death. Mortality increased linearly with increasing APACHE III score on the day of diagnosis. Of initial antibiotic regimens, 67% (26/36) were considered failures. Persistent pneumonia occurred in 35% of patients while recurrent pneumonia was unusual (1/38).

CONCLUSIONS

Development of Pseudomonas pneumonia results in a mortality rate in excess of that due to the presenting illness. The attributable mortality determined by several means appears to approach 40%. The excess mortality appears to be related to the host defense response to the pneumonia rather than any characteristic of the pneumonia. Even standard antibiotic regimens fail frequently and do not prevent the excess mortality. Since at least 38% of deaths can be directly attributable to the Pseudomonas pneumonia, improvement in therapy is needed.

Prophylactic use of the new quinolones for prevention of nosocomial infection in the intensive care unit

The new quinolone antimicrobial agents, particularly those with less activity against anaerobes, selectively prevent colonisation of the alimentary tract by Gram-negative bacilli and staphylococci without substantially affecting the normal anaerobic flora, which preserve the colonisation resistance of the gut. These properties ideally position this class of antibacterial agent for selective decontamination of the digestive tract (SDD) in the prevention of nosocomial infection. The rationale for this procedure is based on the presumption that a significant proportion of infections in compromised patients are endogenous in origin, arising from the host's own microbial flora. If this colonisation by potentially pathogenic microflora within the normal flora can be significantly reduced without being replaced by other more pathogenic microorganisms, the risk of endogenous infection should be minimised. The quinolones have proved to be ideal agents for use in preventing infection in bone marrow transplant and other neutropenic patients. They have been used for SDD in the general intensive care unit population, although the technique has not received widespread acceptance. There have been only 4 reported randomised studies using quinolones as part of SDD regimens and only 301 patients have been evaluated. Although the incidence of ventilator-associated pneumonia has been significantly reduced from 36 to 15%, no effect has been shown on mortality. The cost of using SDD is significantly less with the quinolones than with other regimens, and induction of resistance has not been noted. The new quinolones, and in particular the more recently developed agents with extended Gram-positive activity, appear to be ideally suited for SDD, and their careful evaluation in further large, well designed trials is warranted.

Epidemiology of infection in ICUs

Patients admitted to ICUs are at the greatest risk of acquiring nosocomial infections, partly because of their serious underlying disease, but also by exposure to life-saving invasive procedures. Nosocomial infections increase patient morbidity, increase the length of hospital stay and hospital costs, and may increase mortality rates. When serious infections are suspected, treatment must be commenced immediately to increase the likelihood of a satisfactory outcome for the patient. Empirical knowledge, to select appropriate antibiotics, must be used so that the most likely infecting organisms are treated. In the past this has meant that antibiotics with activity against Gram-negative pathogens were most likely to be selected. However, infections where Gram-positive pathogens are responsible (e.g. Staphylococcus aureus, Staphylococcus epidermidis and enterococci) are increasingly being found. The European Prevalence of Infection in Intensive Care Study (EPIC), the largest point-prevalence study of infection in ICUs in Western Europe was carried out on 28 April 1992. Data on 10,038 patients in 1417 adult ICU departments from 17 countries was collected and analysed. Of the ICU patients surveyed, 21% had at least one infection acquired in an ICU. The most common infections acquired in an ICU were pneumonia (47%), other infections of the lower respiratory tract (18%), infections of the urinary tract (18%) and infections of the blood-stream (12%). The bacterial isolates were equally divided between Gram-negative and Gram-positive species. The commonly reported bacteria were Enterobacteriaceae (34%), S. aureus (30%), Pseudomonas aeruginosa (29%), coagulase-negative staphylococci (19%) and enterococci (12%).

Infections in critically ill patients: experience in MICU at a major teaching hospital

During a one-year period 105 patients suffering a total of 134 infectious episodes were studied prospectively in the medical intensive care unit (MICU). These patients included 54 male and 51 female patients, age ranging from 14 to 100 years (median = 54 years). The overall incidence of infection was 46.7%. Infections acquired in medical wards accounted for 47.8% of the total, followed by community-acquired infections in 27.0%, and MICU-acquired infections in 25.2% of the cases. The most frequent infections were pneumonia and septicaemia accounting for 88% of the total, whereas urinary tract (4.4%), gastrointestinal tract (5.0%), skin and wound infections (2.5%) constituted only 11.5%. The pathogens mainly involved were gram-negative rods, Staphylococcus spp. and Streptococcus pneumoniae. However, in community-acquired pneumonia, the major pathogens were gram-negative rods. In addition, Mycobacterium tuberculosis was an important cause of pneumonia in these patients. The majority of patients had a monoinfection; multiple pathogens were isolated in 11.9% of the episodes. The overall mortality was 46.7%. Several factors that influenced the mortality in these patients were analyzed. Early recognition of these factors may reduce morbidity and mortality.

Overwhelming respiratory failure associated with Legionella pneumophila

Four patients were admitted to the medical intensive care unit at King Khalid University Hospital (KKUH) with overwhelming respiratory failure. Extensive investigations revealed serological evidence of Legionella infection. Three patients required intubation and mechanical ventilation. All patients received erythromycin; rifampin was added to two patients. Two patients survived and two patients died. We report, for the first time in Saudi Arabia, four cases of Legionella pneumophila with severe respiratory failure.

Re-evaluation of pneumonia requiring admission to an intensive care unit: a prospective study

BACKGROUND

Appropriate treatment of severe community and hospital acquired pneumonias requiring admission to a medical intensive care unit depends on knowledge of the likely aetiological agents in any community. Little is known about the pattern and outcome of patients with such pneumonias in Saudi Arabia.

METHODS

In a prospective study 113 patients with pneumonia were investigated in the medical intensive care unit at King Khalid University Hospital, Riyadh, Saudi Arabia between September 1991 and December 1992. The diagnosis was established by microscopy and culture of sputum, blood culture, or serological examination. A standard proforma was used to collect demographic, clinical, and laboratory data.

RESULTS

A microbiological diagnosis was made in 80% of the cases with a single pathogen accounting for 69% of the isolates and multiple pathogens for 11%. Pseudomonas aeruginosa was the most common infecting agent (16%), followed by Streptococcus pneumoniae (12%), Staphylococcus aureus (9%), and Mycobacterium tuberculosis (8%). Pneumonia due to Legionella pneumophilia was diagnosed in three patients and infection due to Mycoplasma pneumoniae in two. These five cases were identified by serological examination. Gram negative rods were the predominant pathogens in both community and hospital acquired pneumonia. The aetiology of pneumonia was not identified in 20% of cases. The overall mortality was 37%. Patients with hospital acquired pneumonia had a higher mortality than those with a community acquired pneumonia. Similarly, a high mortality was found in patients who had a serious underlying disease, abnormal mental state, diastolic blood pressure < 60 mm Hg, blood urea > 7 mmol/l, abnormal liver function tests, serum albumin < 30 g/l, those who required mechanical ventilatory support, and those with APACHE II scores > 20.

CONCLUSIONS

This study highlights two major findings which differ from previous reports on the aetiology of pneumonia. Firstly, Gram negative rods were the predominant pathogens in community acquired pneumonia and secondly, M tuberculosis was an important cause of pneumonia in these patients, indicating that tuberculous pneumonia should be considered in the differential diagnosis of pneumonia in Saudi Arabia.

Impact of previous antimicrobial therapy on the etiology and outcome of ventilator-associated pneumonia

OBJECTIVE

To define the influence of prior antibiotic use on the etiology and mortality of ventilator-associated pneumonia (VAP).

SETTING

A university hospital medical-surgical ICU.

DESIGN

Prospective clinical study.

METHODS

Over a 35-month period, we prospectively studied 129 consecutive episodes of VAP. Etiologic diagnosis was established using a protected specimen brush and quantitative culture techniques. We examined prognostic factors by univariate and multivariate analyses using a statistical software package (SPSS).

RESULTS

The rate of VAP caused by Gram-positive cocci or Haemophilus influenzae was statistically lower (p < 0.05) in the patients who had received antibiotics previously, while the rate of VAP caused by Pseudomonas aeruginosa was statistically higher (p < 0.01). Patients died of causes directly related to the infection in 18 (14.0 percent) episodes, P aeruginosa being isolated in 9 of these fatal cases. Indeed, we found that 27.7 percent (15/54) of patients who had received prior antimicrobial therapy before the onset of pneumonia died, compared with only 4.0 percent (3/75) of those who did not. In the univariate analysis, the variables significantly associated with attributable mortality were age older than 45 years, use of corticosteroids, presence of shock, hospital day of VAP over 9, antecedent COPD, and a prior antibiotic use. A step-forward logistic regression analysis defined only prior antibiotic use (p < 0.0001, OR = 9.2) as significantly influencing the risk of death from VAP. The same result was obtained when severity was included in the model. However, prior antibiotic use entirely dropped out as a significant risk factor when the etiologic agent was included in the regression equation.

CONCLUSIONS

Distribution of infecting microorganisms responsible for VAP differs in patients who received prior antimicrobial therapy, and this factor determines a higher mortality rate. We suggest a restrictive antibiotic policy in mechanically ventilated patients with the purpose of reducing the risk of death from VAP.