Hospital-Acquired Pneumonia (HAP): A Growing Concern

Pneumonia is an important cause of morbidity and mortality in adults with about 5 million cases reported annually in the United States itself. Hospital-acquired pneumonia (HAP) occurs in 0.5-5% of hospitalized patients, with a higher incidence in certain groups like postoperative patients and patients in ICU. It is also called “Nosocomial Pneumonia” or “Health care-associated pneumonia”. It is defined as pneumonia developing more than 48 hours after admission to a health care facility.

The diagnosis of Hospital-acquired pneumonia may be difficult as the clinical features of pneumonia are non-specific and many non-infectious conditions like atelectasis, pulmonary embolus, aspiration, heart failure and cancer, can cause infiltrates on a CXR mimicking a consolidation. This is made more tricky by the difficulty in identifying the organism responsible for the pneumonia due to the high incidence of oropharyngeal colonisation by Gram-negative bacteria. Only 6% of cases of nosocomial pneumonia exhibit a positive blood culture. Ventilator-associated pneumonia (VAP) is a type of nosocomial pneumonia arising >48-72 hours after intubation. It is associated with a higher incidence of multidrug-resistant organisms.

Pathogenesis

Nosocomial pneumonia most likely occurs due to microaspiration of bacteria colonising the upper respiratory tract. Other routes of infection include microaspiration of gastric contents, inhaled aerosols, haematogenous spread, spread from pleural space and direct inoculation from Hospital/ICU personnel.

Clinical Diagnosis

The diagnosis of Nosocomial pneumonia is based on the time of onset i.e. it develops more than 48 hours after admission to a health care facility, CXR changes, clinical features and simple laboratory investigations or the result of quantitative microbiology.

Clinically, HAP is diagnosed by the finding of a new infiltrate or a change in an infiltrate on CXR and growth of pathogenic organisms from sputum plus one of the following:

• WBC count: > 12 x 10⁵/Litre
• Core body temperature: ≥ 38.3°C
• Sputum Gram stain Scores: more than 2 on a scale of 4 of polymorphonuclear leukocytes and bacteria.

Investigations

A parallelism exists in the investigations required for the diagnosis of HAP and CAP.

• CXR: Most definitions of nosocomial pneumonia require the presence of new persistent infiltrates on a CXR.
• Respiratory secretions: Certain organisms are always pathogenic and are indicative of an infection when found in tracheal aspirates.
• Blood cultures: This helps in identifying the aetiological agent in 8-20% of patients. Bacteraemia is associated with a worse prognosis. In 50% of patients with severe hospital-acquired pneumonia and positive blood cultures, there is another source of sepsis.

Management

The initial selection of antibiotics is made on the basis of epidemiological clues until quantitative microbiology results are obtained. It is important that antibiotics should be instituted within 1 hour of diagnosis. The microbiological investigations are used to narrow down the microbial cover based on sensitivity. Treatment should be reassessed after 2-3 days or sooner if the patient deteriorates.

Recommended Initial Empiric Treatment for Nosocomial Pneumonia

• No risk factors for multidrug-resistant pathogens : Cefotaxime or Levofloxacin, Moxifloxacin or Ciprofloxacin or Ampicillin/Sulbactam or Ertapenem
• Antimicrobial therapy in previous 90 days or Current hospitalisation for ≥ 5 days or High frequency of antibiotic resistance in the specific hospital unit or Hospitalisation for 2 days or more in previous 90 days or Residence in nursing home or extended-care facility or Home infusion therapy (including antibiotics) or Chronic dialysis within 30 days or Home wound care or Family member with multidrug-resistant pathogen or Immunosuppression or Bronchiectasis : One of: Antipseudomonal cephalosporin (Cefepime or Ceftazidime) or Antipseudomonal Carbapenem (Meropenem or Imipenem-Cilastatin) or β-lactam/β-lactamase inhibitor (Piperacillin-Tazobactam or Cefoperazone-Sulbactam) plus one of: Aminoglycoside or Antipseudomonal quinolone (Levofloxacin or Ciprofloxacin) plus one of the following for patients at high risk of methicillin-resistant Staphylococcus aureus (MRSA) infection: Linezolid or Vancomycin or Teicoplanin

Duration of Therapy

Current ATS guidelines recommend 7 days’ treatment provided the aetiological agent is not P. aeruginosa and the patient has a good clinical response with resolution of clinical features of infection. There is no significant difference in the clinical outcome of those who receive treatment for 8 days or 14 days for ventilator-associated pneumonia.

Response to Therapy

At least 48-72 hours of therapy should have elapsed to notice any clinical improvement. Interestingly, the CXR is of limited value for assessing response as there is an initial deterioration and improvement in CXR often lags behind clinical response. However, a rapidly deteriorating CXR pattern with a > 50% increase in size of infiltrate in 48 hours, new cavitation or a significant new pleural effusion should raise concern.

If the patient fails to respond reconsider the diagnosis, host factors and therapeutic factors. Review the antibiotics and repeat cultures. It may be useful to broaden the antibiotic coverage while waiting for the results of the investigations. Consider invasive sampling of respiratory secretions, CT or ultrasonography of the chest to look for an empyema or abscess, another source of infection, open-lung biopsy to establish diagnosis and aetiology, or administration of steroids.

Prevention

Measures recommended by the Centers for Disease Control (CDC) include:

• hand-washing, nursing patients in a 30° head-up position
• subglottic aspiration of secretions
• orotracheal rather than nasotracheal intubation
• changing the breathing circuit only when visibly soiled or mechanically malfunctioning
• preferential use of non-invasive ventilation.

Last Words

Hospital-Acquired or Nosocomial Pneumonia has been of primary importance in most tertiary health-care facilities due to the rampant use of high-end antibiotics which could otherwise have been avoided. The rampant use of antibiotics has resulted in “superbugs” that are resistant to all existent antibiotics and this has created a growing awareness among health care professionals. We ought to be judicious in our use of antibiotics and should follow recommended guidelines to avoid any more damage that might result out of our complacency.