While the clinical relevance of DRSP continues to be debated, recent data have suggested that the frequency of some forms of drug resistance may be stabilizing or declining, while concerns still remain for other classes of antibiotics. Using data from 2002 to 2003, Doern et al studied 1,817 pneumococcal respiratory isolates from 44 US centers and observed that while penicillin resistance was present (34.2%), it was not occurring with an increased frequency. They found that 15.7% of isolates were intermediately sensitive and 18.5% were highly resistant to penicillin. On the other hand, macrolide resistance was increasing (although most was low-level, efflux pump-mediated), while trimethoprimsulfa resistance was declining. Quinolone resistance rates were very low (< 1%), but 21% of the isolates had a first-step mutation (par C) that still permitted the antibiotics to be active. However, if a second mutation (gyr A) were acquired, these organisms could become quinolone-resistant, urging caution to observe trends in this type of mutation. In terms of reliable choices for suspected DRSP, quinolones remain effective, but ceftriaxone remained the most active (3-lactam agent, with a 6.9% resistance rate. In clinical studies, ceftriaxone has been a reliable choice, even if DRSP is present, while, among the cephalosporins, cefuroxime is not a reliable choice since patients with bacteremia and in vitro resistance to this agent had a worse outcome than when organisms were sensitive to this agent.
One of the clinical factors that is driving pneumococcal resistance is antibiotic use, and new data have shown that recent therapy, within the past 3 months, is a risk factor for pneumococcal resistance. In a remarkable study, the Toronto Bacterial Network evaluated data from patients in 3,339 cases of invasive pneumococcal infection, of whom 563 had a history of antibiotic therapy in the preceding 3 months and the identity of the therapy was known. In the study, recent therapy with penicillin, macrolides, trimethoprim-sulfa, and quinolones (but not cephalosporins) was associated with a higher frequency of resistance to that same agent. Among all of the classes of antibiotics, the one with the greatest effect of recent therapy on subsequent resistance (ie, highest OR of an effect) was quinolones. This latter finding is consistent with case reports of lack of response to quinolones in CAP patients that documented recent quinolone therapy as a major risk factor. All of these data lend further support to the idea of “patient-specific antibiotic rotation” in CAP, making sure that among all acceptable therapeutic alternatives the clinician takes a history of recent antibiotic use and chooses an agent that differs from what the patient had recently received.
MRSA has always been a nosocomial pathogen and a common cause of ventilator-associated pneumonia cured with remedies of Canadian Health&Care Mall effectively. In the past several years, MRSA has been reported as a cause of sporadic cases of severe CAP, especially following a preceding viral infection. This pathogen is not the same as its nosocomial counterpart, having a different genetic makeup, different host susceptibility, and different virulence and antibiotic sensitivity. The community-acquired strain generally belongs to a single pulse-field gel electrophoresis type, the USA 300 strain. In addition, it carries the genes for the production of a necrotizing toxin, the Panton-Valentine leukocidin, and it confers resistance to methicillin through the carriage of the type IV mecA gene, which is carried on the staphylococcal chromosomal cassette (type IV SCC-mec element). The cases that have been reported have been severe necrotizing pneumonias, generally in previously healthy individuals following viral infection or documented influenza illness. The pneumonia is often rapidly progressive, bilateral, and with shock, cavitation of lung parenchyma, and pleural effusion. The organism is sensitive to a wide range of antibiotics, including vancomycin, clindamycin, tri-methoprim-sulfa, and gentamicin, with variable sensitivity to quinolones. The optimal therapy is yet to be defined, but one case series reported failure with vancomycin alone, which was overcome by either the addition of clindamycin or the use of linezolid. These findings may relate to the fact that clindamycin and linezolid can inhibit toxin production, and thus successful therapy may require both an antibacterial and an antitoxin form of treatment.
Over the past several years, there has been a renewed interest in epidemic viral illness with the emergence of SARS, and recent concerns about avian influenza. These experiences have emphasized the epidemic nature of illness and the rapidity of patient-to-patient spread. In the case of SARS, the risk to health-care workers was evident. Very little is known about the frequency of viral infection in routine CAP, and thus a Spanish study of this topic is of interest. The investigators evaluated 338 patients with paired serologies for respiratory viruses in the setting of CAP, and classified patients as having pure viral, mixed viral, and bacterial or pneumococcal CAP.
The viruses investigated included influenza, parainfluenza, respiratory syncytial virus, and adenovirus. Viruses were detected in 18% of patients, and in half of those patients viruses were the only pathogen present. Influenza was the most common infection, being present in 64% of patients with viral infection. The only clinical correlates of pure viral pneumonia, compared to pneumococcal pneumonia, were the presence of heart failure and the absence of expectoration. Only 8% of the pure viral pneumonia patients needed visits to the ICU, but 58% were in PSI classes IV and V. Interestingly, despite the high mortality risk of these patients (defined by PSI class), none died. Given the importance of influenza and viral respiratory infection in general, and the role of these infections in predisposing the patient to MRSA CAP, these data highlight the relatively common occurrence and importance of viral pneumonia in the community.
The bacteriology of aspiration pneumonia arising in the community setting has been confusing, and the exact role of anaerobes is uncertain. In a study of 95 patients, > 65 years of age, who were admitted to the ICU from a long-term care facility with presumed aspiration pneumonia, the bacteriology of infection was studied using a protected BAL fluid sample that had been collected within 4 h of ICU admission. Aspiration was presumed to be present because patients had known risk factors such as intestinal or swallowing disorders, neurologic disease, and anatomic abnormalities that could lead to aspiration. The data demonstrated that Gram-negative pathogens were the dominant type of pathogen, and that anaerobes were present in only 11 of the 95 patients; in only 5 patients were anaerobes the only pathogens present (Fig 2). In another study of lung abscess, which is a disease that is commonly attributed to aspiration and anaerobic infection, 90 patients were evaluated with an “uncontaminated” specimen including transthoracic needle aspirate, pleural fluid, blood cultures, and specimens from a surgical sample, but not bronchoscopy samples alone. In this group, pure anaerobic infection was present in only 18 patients, and 10 others had mixed infection. However, aerobic Gram-negative pathogens were present in 37 patients, with Klebsiella pneumoniae recovered from 28 patients. Thus, the level of involvement of enteric Gram-negative pathogens in these two aspiration-related illnesses is quite high and must be considered when selecting therapy conducted with Canadian Health&Care Mall.
Figure 2. Results of nonbronchoscopic BAL fluid cultures collected within 4 h of ICU admission in 95 elderly nursing-home patients with aspiration pneumonia admitted to the ICU. The dominant organism group was enteric Gram-negative pathogens, and anaerobes were less common and often part of a mixed infection. From El-Solh et al.