Infection Control Today - 05/2003: Fighting Nosocomial Pneumonia

Fighting Nosocomial Pneumonia

By John Roark

Nosocomial pneumonia, or Hospital-Acquired Pneumonia (HAP) is a serious illness associated with substantial morbidity and mortality rates. It is the second most common nosocomial infection, but the infection most frequently associated with a fatal outcome. The annual incidence is five to 10 cases per 1,000 admissions, but this can increase up to 20-fold in ventilated patients.1

Risk factors for nosocomial pneumonia include mechanical ventilation for more than 48 hours, residence in an intensive care unit (ICU), duration of hospital stay, severity of underlying illness and presence of co-morbidities. Optimum therapy for HAP should take into account severity of illness, demographics, specific pathogens involved, and risk factors for antimicrobial resistance. Previous antibiotic use before onset of nosocomial pneumonia raises the likelihood of infection with highly virulent organisms, such as Pseudomonas aeruginosa and Acinetobacter sp.

Antimicrobial resistance has escalated dramatically worldwide in the past two decades. The National Nosocomial Infections Surveillance System (NNIS), which incorporates data from community, university and municipal hospitals, clarified the major pathogens responsible for HAP in the United States since the 1970s. During this time, some pathogens have emerged as important opportunistic pathogens in ICUs (Acinetobacter, methicillin-resistant Staphylococcus aureus [MRSA] and Enterobacter), whereas the prevalence of other pathogens (Klebsiella pneumoniae and Pseudomonas aeruginosa) has remained stable or declined. S. aureus was implicated in 13 percent of HAP from 1981 to 1986, 16 percent from 1986 to 1989, and 19 percent from 1990 to 1996. During these intervals, Enterobacter was implicated in 7 percent, 11 percent, and 11 percent of cases of HAP, respectively.

The prevalence of K. pneumoniae during these time periods was 12 percent, 7 percent, and 8 percent, respectively. The prevalence of P aeruginosa remained constant, causing 17 percent of HAP during each of these time periods. The increasing prevalence of Enterobacter reflects selection pressure from heavy use of third-generation cephalosporins (particularly ceftazidime), which facilitates evolution of chromosomal inducible [Beta]-lactamases. S. aureus has also increased in frequency as a cause of nosocomial infections, bacteremias and pneumonias. An analysis of 112 ICUs from 97 National Nosocomial Infections Surveillance System hospitals from 1992 to 1997 cited S. aureus as a cause of 20 percent of HAPs and 13 percent of bacteremias. Liberal use of intravascular catheters and nasal carriage of S. aureus are major risk factors for pneumonia caused by this pathogen. Currently, more than 30 percent of nosocomial isolates of S. aureus in the United States are resistant to methicillin. 2

The Centers for Disease Control and Prevention's (CDC) Hospital Infection Control Practices Advisory Committee (HICPAC) revised its Guidelines for Prevention of Nosocomial Pneumonia in 1994. The guideline addresses common problems encountered by infection control practitioners regarding the prevention and control of nosocomial pneumonia in U.S. hospitals. Sections on the prevention of bacterial pneumonia in mechanically ventilated and/or critically ill patients, care of respiratory-therapy devices, prevention of cross contamination, and prevention of viral lower respiratory tract infections, such as respiratory syncytial virus (RSV) and influenza infections have been expanded and updated.

The study states, "Most patients with nosocomial pneumonia are those with extremes of age, severe underlying disease, immunosuppression, depressed sensorium and cardiopulmonary disease, and those who have had thoraco-abdominal surgery. Although patients with mechanically assisted ventilation do not comprise a major proportion of patients with nosocomial pneumonia, they have the highest risk of developing the infection."

Most bacterial nosocomial pneumonias occur by aspiration of bacteria colonizing the oropharynx or upper gastrointestinal tract of the patient. Intubation and mechanical ventilation greatly increase the risk of nosocomial bacterial pneumonia because they alter first-line patient defenses. Pneumonias due to Legionella spp, Aspergillus spp and influenza virus are often caused by inhalation of contaminated aerosols. RSV infection usually follows viral inoculation of the conjunctivae or nasal mucosa by contaminated hands.

Traditional preventive measures for nosocomial pneumonia include decreasing aspiration by the patient, preventing cross contamination or colonization via hands of personnel, appropriate disinfection or sterilization of respiratory-therapy devices, use of available vaccines to protect against particular infections, and education of hospital staff and patients. New measures under investigation involve reducing oropharyngeal and gastric colonization by pathogenic microorganisms.

Ventilator-Associated Pneumonia

In mechanically ventilated patients, the incidence of nosocomial pneumonia ranges from 9 to 68 percent, and mortality ranges from 33 to 71 percent. Despite the frequency of ventilator-associated pneumonia (VAP) and the threat it poses to patient survival, consensus on an appropriate diagnostic strategy for VAP has yet to be established.

In a1988 study of 147 mechanically-ventilated patients, a clinical diagnosis of bacterial pneumonia was strongly suggested by the presence of fever, leukocytosis, pulmonary infiltrates and purulent sputum. Yet less than half of these patients had positive cultures from specimens obtained bronchoscopically by protected catheter brushing (PCB). In the 10 years following this report, numerous studies have evaluated the performance characteristics of a variety of techniques for obtaining and culturing specimens. Nevertheless, the utility of these techniques in directing appropriate patient care remains controversial.3

Slashing Pneumonia Rates

When HAP rates escalated at St. Luke's Episcopal Hospital in Houston, quality improvement leaders knew it was time to find a solution. After soliciting ideas from a multidisciplinary team, the hospital achieved an astounding 50 percent reduction in its nosocomial pneumonia rates without any major expenditures or complicated changes in clinical care.

Though the project itself was intensive, the actual solutions to the nosocomial pneumonia problem turned out to be as simple as handwashing and suctioning. In addition, the hospital developed a tool for determining which patients are at high risk so they can receive preventive care as early as possible. After five years, the quality improvement project has been a major success, says Rosemary Luquire, RN, PhD, senior vice president for patient care and chief quality officer.

Luquire worked with Susan Houston, RN, PhD, CNAA, FAAN, assistant vice president of clinical management and outcomes research, to develop the quality improvement project. Nosocomial pneumonia rates began to increase significantly in 1994, when the rate was 4.7 per 1,000 patient days per year. In 1996, the rate had reached 6.5.

"In 1996 we saw that we would top off the year at a high rate. Although we do a lot of work with infections, we had the greatest opportunity to reduce nosocomial pneumonia because it was increasing at a faster rate than the others," Houston says. "We got together a multidisciplinary practice collaborative team with nurses, physicians, pharmacists, infection control practitioners, administrators and (many) others."

The team created a fishbone diagram listing the different causes of nosocomial pneumonia. With brainstorming and educated guesses, many potential causes were identified, from hand-washing practices to reuse of disposables, patient location, and the retaping and rotating of endotracheal tubes. The team sought verification that those causes actually led to nosocomial pneumonia infections, but found that there was no literature to support many of those supposed causes.

"We found that many of the things we think cause pneumonia are just gut thinking, hypothetical and not actually supported by any data," Houston says. "Our literature review also revealed that most of the research has been done on patients with emphysema, chronic obstructive pulmonary disease (COPD) and asthma. But most of our cases are in cardiovascular surgery patients."

The team conducted a case-control study of 240 medical records and plotted the causes of nosocomial pneumonia on their fishbone diagram. Their study revealed that four particular factors were most strongly associated with the patients who developed infections:

  • Renal failure
  • Use of intra-aortic balloon pumps
  • Reintubation
  • Total intubation time

The analysis showed that those four factors were strongly associated with infections, so the team hoped they could be used to identify patients at risk and also develop a protocol to address those issues.

Based on their findings, the team developed and implemented a nosocomial pneumonia prevention protocol, which caused rates to drop from 6.5 to 4.6 in a year. They knew it was working, so they focused on some other factors as well.

The quality improvement team studied the hand washing and suctioning practices at the hospital and found ample room for improvement. The team updated the policies and procedures for both, then sent observers periodically to monitor how well staff followed them. The hospital still conducts in-person monitoring every so often to keep staff aware of the need for good handwashing and suctioning techniques, and there is discussion about implementing video monitoring.

"People always do it better when they know someone is watching," Houston says. "Then it drops off slowly as people become complacent, so we come back and stand there again, looking over their shoulders as they wash their hands. It raises the awareness level again."

The quality initiatives have been in place for about five years now, and Houston and Luquire say the project is a major success. The nosocomial pneumonia infection rate dropped from 6.5 per 1,000 patient days in 1996 to 2.8 in 2001, putting the hospital in about the 15th percentile of the infection rates collected by the CDC.

Those good results came with very little investment. Houston says the hospital spent roughly $20,000 on the project itself, and the pneumonia prevention protocol costs about $30 per patient. A single nosocomial pneumonia infection costs the hospital about $8,000, so Houston says the project's costs were recovered once it prevented only a few infections. With the lowered infection rates, she estimates the hospital avoids about 100 pneumonia infections per year.3

Potential Prevention

Promising preventive modalities for nosocomial pneumonia include use of a semi-recumbent position (elevating the head of the bed 45 degrees), endotracheal tubes that allow continuous aspiration of secretions, and heat and moisture exchangers.

Rita McCormick, RN, senior infection control practitioner for the University of Wisconsin Hospitals and Clinics, cautions that the semi-recumbent approach may be easier said than done.

"When it comes right down to it, it's difficult. You would like to keep the patient elevated at about 30 degrees. For some, that will be contraindicated because of other injuries. It's one thing to lie on your back and have someone put your head up 30 degrees. But they want to get you off your back, so they turn you on your side. Now put their head up 30 degrees and they're cranked in the middle. That's not very comfortable. Other people say you can get around that by doing a reverse-Trendelenburg. You lower the feet, you raise the head, so they're lying on their side on a straight plane. But now they're going to slide down to the end of the bed. Then you have shirring forces of the skin and soft tissue. On some patients, that will result in significant tissue damage."

Most nosocomial pneumonias are caused by organisms that have been aspirated from the upper airway or through the endotracheal tube. Thus, measures that minimize the risk of aspiration of orogastric material into the tracheobronchial tree may reduce the incidence of pneumonia. Although a cuffed endotracheal tube is commonly thought to prevent aspiration, in fact secretions tend to pool above the cuff and leak between the cuff and tracheal wall, permitting seeding of the airway. The semirecumbent position appears to reduce the volume of aspirated secretions compared with the supine position. In one study, the simultaneous culture of the same microorganisms from gastric, pharyngeal, and endotracheal aspirates was observed in 68 percent of samples taken from 19 patients while they were supine and 32 percent of samples taken while these same patients were semirecumbent. Valles and colleagues reasoned that if the secretions pooled above the endotracheal tube cuff represent an important reservoir of colonizing bacteria, then removing this pool may decrease the incidence of VAP. They described an ingenious endotracheal tube design with an additional lumen ending above the cuff through which secretions above the cuff (subglottic) could be aspirated and removed. On studying 153 patients randomized to either a standard endotracheal tube (control subjects) or one through which subglottic secretions could be continuously aspirated, they found a significantly decreased incidence of VAP in the continuous aspiration vs. control group.4

"The point, in terms of preventive measures, has been to do some things like making the nurses chart every four hours on a patient that is being ventilated -- are they in the right position?" says McCormick. "They might be at that moment, but a couple of minutes later they put them flat and they do something else. The whole reason you're doing this is so that the fluid that may be in their GI track and belly doesn't retrograde up and slip down into the respiratory tract. Bottom line is, it's easier said than done."

SARS and Global Surveillance

By John Roark

The recent outbreak of severe acute respiratory syndrome (SARS) has been a wake-up call to the importance of being prepared for the unexpected. Complacency in the United States and other countries regarding infectious diseases as being in a state of control has given way to an awareness of the responsibility of public health systems at a local, state, national and global level to address and control infectious diseases.

The World Health Organization (WHO), of which the Centers for Disease Control and Prevention (CDC) is a member, is leading an international effort to address this threat. The Institute of Medicine's recently released "Report on Microbial Threats to Health" is a follow-up to a 1999 report that the Institute of Medicine issued titled, "Emerging Infections: Microbial Threats to Health in the United States."

SARS is a dramatic example of the importance of global surveillance and response, and the importance of good working relationships between WHO, WHO regional offices, country offices and ministries of health.

In a March 18, 2003 press teleconference, James Hughes, MD, assistant surgeon general and director of the CDC's National Center for Infectious Diseases, addressed issues of concern, including SARS.

"The SARS experience reinforces the need to strengthen global surveillance, to have prompt reporting, to have it linked to adequate and sophisticated diagnostic laboratory capacity," Hughes said. "It's a reminder that we need better capacities to move diagnostic specimens from remote settings where these diseases often appear to get them to reference laboratories."

Hughes cited the WHO's need to access information on outbreaks or clusters of unexplained illnesses, regardless of where they occur. "People need to recognize that these clusters can have global implications, and this is a dramatic example of that. The idea of creating databases for local hospitals to track symptoms that might be suspicious is something that I think people are saying would be especially useful with SARS, which does start with some fairly nonspecific symptoms."

Hughes sees clinicians as important partners in surveillance of naturally occurring and purposely caused disease. Sentinel surveillance networks collaborate with the Infectious Diseases Society of America (IDSA) to provide updated information, and the CDC also hears from patients, clinicians, doctors and travel clinics, and has set up a 24 hour hotline to handle clinician calls.

Lin Chen, MD, director of the Travel Resource Center at Mt. Auburn Hospital in Cambridge, Mass., credits the availability of up-to-date information as an invaluable tool.

"When the SARS outbreak was first reported, the first thing that struck me was that our communication channels are so much better now because of the networks of communication where reports of the outbreak are posted very quickly," she said. "I received information about the travel advisories that were going to be released even before they went to press from some of these networks. As a result of the new networks that have been set up through Web sites or emails, the dissemination of information has been very rapid, all the way down to the primary care physicians; most people who are taking care of patients are aware of the events."

Chen credits GeoSentinel, a network of travel/tropical medicine clinics initiated in 1995 by the International Society of Travel Medicine (ISTM) and the CDC as a vital information tool. GeoSentinel is based on the concept that clinics are ideally situated to effectively detect geographic and temporal trends in morbidity among travelers, immigrants and refugees.

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