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COMMENTARY |
Departments of Pediatrics and of Epidemiology and Public Health
Yale University School of Medicine
New Haven, CT 06520-8064
Abbreviations: VAP, ventilator-associated pneumonia • CDC, Centers for Disease Control and Prevention • NNIS, National Nosocomial Infections Surveillance System
The diagnosis of pneumonia in intubated, ventilated patients is difficult to confirm. This relates to the lack of specificity of physical examination findings, diagnostic imaging, cultures, and other laboratory tests. Organisms recovered from the upper airway or by suction through an endotracheal tube may be colonizers and not represent lower respiratory flora. Even bronchoscopic specimens may be contaminated by pharyngeal flora. Advances have been made in diagnosing adult ventilator-associated pneumonia (VAP) by quantitating the number of organisms recovered in bronchoalveolar lavage fluid. Organisms recovered in large numbers are the presumed etiologic agent.1,2
This problem is more challenging for diagnosing the intubated newborn because of the lack of specimens other than secretions suctioned through an endotracheal tube and the ease with which the neonate is colonized by organisms transmitted from the environment or from caretakers.3 For the purpose of performing surveillance, the Centers for Disease Control and Prevention (CDC) published recommendations in 1988 that included special criteria for the infant <1 year old.4 Recently this was updated for CDC-sponsored surveillance studies such as National Nosocomial Infections Surveillance System (NNIS).2 The problem with these recommendations is the lack of a "gold standard" with which to compare any of the surveillance studies. The diagnostic value of the CDC surveillance recommendations for infants is unknown other than for following year-to-year trends. For these reasons (difficulty of diagnosis and lack of validations of the standards), there have been few studies of VAP in neonates. Treatment of VAP is generally with antibiotics used for neonatal sepsis, because there is a great deal known about the organisms causing neonatal bloodstream infections.5
In this issue, Apisarnthanarak et al6 bravely look at VAP in preterm neonates in the neonatal intensive care unit. The authors examine the epidemiologic features of premature infants with VAP, analyze putative risk factors, and enumerate the organisms presumably responsible for VAP. They state that "the CDC/NNIS definitions for infants 
12 months were used for nosocomial infections, specifically bloodstream infections and ventilator-associated pneumonia."6 Later they state that "associated organisms were designated as those organisms recovered from tracheal aspirates or bronchoalveolar lavage." The first problem is that, although the CDC definitions paper is a frequently used reference for epidemiologic surveillance, it is not validated for microbial diagnosis or descriptive clinical research. Second, although this reference contains criteria for the diagnosis of pneumonia, there is nothing specifically about VAP, although this is addressed in the newer criteria where endotracheal aspirates are specifically considered unsuitable.2
Although it is true that the 1988 NNIS guidelines allow for the diagnosis of nosocomial pneumonia in an infant to be made on the basis of a new or progressive infiltrate and isolation of a respiratory pathogen, an infiltrate in the chest radiograph of an intubated premature neonate may represent hyaline membrane disease, progression of meconium aspiration, early development of bronchopulmonary dysplasia, or atelectasis. Apisarnthanarak et al6 state that expert review of the cases ruled out other conditions, but we must accept this on faith. Thus, some or many of the organisms recovered from tracheal aspirates may represent colonization rather than causes of VAP. Therefore the interesting data presented by Apisarnthanarak et al should be a first step in discovering the causes of VAP in premature infants, but more research is needed in developing criteria for diagnosing VAP in the newborn.
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FOOTNOTES |
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Address correspondence to Robert S. Baltimore, MD, Department of Pediatrics, Yale University School of Medicine, Box 208064, New Haven, CT 06520-8064. E-mail: robert.baltimore{at}yale.edu
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REFERENCES |
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This article has been cited by other articles:
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  D. Kaufman and K. D. Fairchild Clinical Microbiology of Bacterial and Fungal Sepsis in Very-Low-Birth-Weight Infants Clin. Microbiol. Rev., July 1, 2004; 17(3): 638 - 680. [Abstract] [Full Text] [PDF]
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