Congenital Pneumonia Workup

Updated: Mar 01, 2016
  • Author: Muhammad Aslam, MD; Chief Editor: Ted Rosenkrantz, MD  more...
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Workup

Approach Considerations

Diagnostic criteria for congenital pneumonia remain controversial in the absence of histopathologic specimens. Criteria range from very liberal (to minimize the probability of missing a case) to very stringent (to minimize the possibility of labeling some other condition inappropriately). An example of the former includes only respiratory difficulties and persistent radiographic evidence of infiltrates.

More stringent standards often also mandate the presence of respiratory support requirements, laboratory markers of systemic inflammation, and inflammatory respiratory secretions (using quantitative or semiquantitative threshold criteria). Diagnosis in the clinical setting is usually based on a combination of historical, physical, radiographic, microbiologic, and laboratory findings.

Go to Pneumonia, Pediatric and Afebrile Pneumonia Syndrome for more complete information on these topics.

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Radiography

Numerous radiographic patterns are consistent with neonatal pneumonia and a multitude of other pathologic processes. [26] (See the images below.) A synthesis of all available information and careful consideration of the differential diagnosis is essential to establishing the diagnosis, although empiric antimicrobial treatment usually cannot be deferred because of inability to prospectively exclude the diagnosis.

Anteroposterior chest radiograph in an infant born Anteroposterior chest radiograph in an infant born at 28 weeks' gestation was performed following apnea and profound birth depression. Subtle reticulogranularity and prominent distal air bronchograms were consistent with respiratory distress syndrome, prompting exogenous surfactant and antimicrobial therapy. Initial smear of endotracheal aspirate revealed few neutrophils but numerous, small, gram-negative coccobacilli. Culture of blood and tracheal aspirate yielded florid growth of nontypeable Haemophilus influenzae.
Full-term infant (note ossified proximal humeral e Full-term infant (note ossified proximal humeral epiphyses, consistent with full term) with progressive respiratory distress from birth following delivery to a febrile mother through thick, particulate, meconium-containing fluid and recovery of copious meconium from the trachea. Right clavicle is fractured without displacement. Note the coarse dense infiltrates obscuring the cardiothymic silhouette bilaterally with superimposed prominent air bronchograms. Listeria monocytogeneswas recovered from the initial blood culture.
Patchy infiltrates most prominent along left cardi Patchy infiltrates most prominent along left cardiothymic margin in a full-term infant (note proximal humeral ossific nuclei) born to an afebrile woman 18 hours after membranes ruptured. The infant was initially vigorous but developed gradual onset of progressive respiratory distress beginning at 2 hours and prompting endotracheal intubation and transfer to a tertiary center at age 10 hours. Note blunting of the right costophrenic angle, a thin radiodense rim along the lateral right hemithorax, and a fluid line in the right major fissure, all consistent with pleural effusion. Gram staining of pleural fluid recovered at thoracentesis indicated occasional gram-negative bacilli. Tracheal aspirate, pleural fluid, and blood all yielded Escherichia coliupon culture. The dense right upper lobe may appear to suggest lobar infiltrate, but upward bowing of the fissure is more suggestive of volume loss, as in atelectasis, than the bulging picture expected with dense pneumonic change. This lobe appeared normal and appropriately inflated on a subsequent film 2 hours later, also suggestive of atelectasis. Umbilical venous catheter and endotracheal tube were positioned properly on the follow-up film.

A well-centered, appropriately penetrated, anteroposterior chest radiograph is essential. Other views may also be warranted, to clarify anatomic relationships and air-fluid levels.

Be aware that any image reflects conditions only at the instant when the study was performed. Because neonatal lung diseases, including pneumonia, are dynamic, initially suggestive images may require reassessment based on subsequent clinical course and findings in later studies.

When considering pneumonia, devote particular attention to the following:

  • Costophrenic angles

  • Pleural spaces and surfaces

  • Diaphragmatic margins

  • Cardiothymic silhouette

  • Pulmonary vasculature

  • Right major fissure

  • Air bronchograms overlying the cardiac shadow

  • Lung expansion

  • Patterns of aeration

Diffuse relatively homogeneous infiltrates that resemble the ground-glass pattern of respiratory distress syndrome are suggestive of a hematogenous process, although aspiration of infected fluid with subsequent seeding of the bloodstream cannot be excluded.

Patchy irregular densities that obscure normal margins are suggestive of antepartum or intrapartum aspiration, especially if such opacities are distant from the hilus. Patchy irregular densities in dependent areas that are more prominent on the right side are more consistent with postnatal aspiration.

Generalized hyperinflation with patchy infiltrates suggests partial airway obstruction from particulate or inflammatory debris. However, the contribution of positive airway pressure from respiratory support must also be considered.

Pneumatoceles (especially with air-fluid interfaces) and prominent pleural fluid collections also support the presence of infectious processes.

Single or multiple prominent air bronchograms 2 or more generations beyond the mainstem bronchi reflect dense pulmonary parenchyma (possibly an infiltrate) highlighting the air-filled conducting airways.

A well-defined dense lobar infiltrate with bulging margins is unusual.

Lateral or oblique projections may help to better define structures whose location and significance are unclear.

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Ultrasonography

Ultrasonography may be helpful in selected circumstances. Ultrasonography is particularly useful for identifying and localizing fluid in the pleural and pericardial spaces. However, the presence of air within the lungs limits the use of ultrasonography.

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Computed Tomography or Magnetic Resonance Imaging

CT or MRI may be helpful for evaluating the following:

  • Suspected tumors

  • Aberrant vessels

  • Sequestered lobes

  • Other primary pulmonary anomalies

CT or MRI is also helpful for establishing the presence of infiltrate, atelectasis, or other acquired processes. Such studies may be particularly useful for localizing infiltrates, abscesses, or infected fluid before percutaneous sampling attempts

Go to Imaging in Pediatric Pneumonia for more complete information on this topic.

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Cultures

The most useful laboratory tests for congenital pneumonia facilitate the identification of an infecting microorganism. Results can be used for therapeutic decisions as well as prognostic and infection control considerations.

Conventional bacteriologic culture is used most widely and is currently most helpful. Aerobic processing is sufficient for recovery of most responsible pathogens. Although the foul smell of amniotic fluid in the setting of maternal chorioamnionitis is often attributable to anaerobes, these organisms are seldom shown to be causative.

Culture of fungi, viruses, U urealyticum,U parvum, and other nonbacterial organisms often requires different microbiologic processing but may be warranted in suggestive clinical settings.

A number of factors may interfere with the ability to grow a likely pathogen, including (but not limited to) the following:

  • Pretreatment with antibiotics that limit in vitro but not in vivo growth

  • Contaminants that overgrow the pathogen

  • Pathogens that do not replicate in currently available culture systems

  • Presence of a process that is inflammatory but not infectious, such as meconium aspiration

Techniques that may help overcome some of these limitations include antigen detection, nucleic acid probes, PCR-based assays, or serologic tests. Although once widely used, tests such as latex agglutination for detection of group B streptococcal antigen in urine, serum, or other fluids have fallen into disfavor because of poor predictive value; however, new generations of non–culture-based technologies continue to undergo development and may be more accurate and widely available in the future.

Blood culture

Blood culture with at least 1 mL of blood from an appropriately cleaned and prepared peripheral venous or arterial site is essential because many neonatal pneumonias are hematogenous in origin and others serve as a focus for secondary seeding of the bloodstream. Blood culture samples drawn through freshly placed indwelling vascular catheters may be helpful, but the possibility of contamination rises the longer the catheter is in place. Contemporary automated microbiologic processing systems facilitate differentiation of true pathogens from contaminants, since the former are usually recovered within 12-24 hours, while the latter frequently take much longer.

Multiple cultures of blood from different sites and/or those drawn at different times may increase culture yield, but limited circulating blood volume precludes this as the standard of care in neonates on the first day of life.

Cerebrospinal fluid culture

Routine culture and analysis of cerebrospinal fluid (CSF) in infants in whom congenital pneumonia is suspected is controversial because the yield is low and many infants with respiratory support requirements do not tolerate lumbar puncture well. However, CSF may yield a pathogen when blood does not, especially following maternal antibiotic pretreatment. [27] In addition, the presence of a pathogen in the CSF may indicate the need for alteration in the selection, dosage, and duration of antibiotic therapy even if cultures from other sites yield the same organism.

Culture of specimens from endotracheal aspiration

Culture and Gram stain of an endotracheal aspirate obtained by aseptic technique as soon as possible after intubation may be useful. Under typical circumstances, airway commensals take as long as 8 hours to migrate down the trachea. At least one study demonstrated that culture of endotracheal aspirates obtained within 8 hours of birth correlates very well with blood culture results and probably reflects aspirated infected fluid. [28]

The longer the endotracheal tube has been in place, the greater the likelihood that recovered organisms represent colonizing organisms rather than invasive pathogens. Nonetheless, recovery of a single recognized pathogen in large quantities may be helpful in the selection of antibiotic therapy, especially if culture results from normally sterile sites are negative.

The absence of significant inflammatory cells in an endotracheal aspirate or other respiratory specimen suggests that organisms recovered from that site are unlikely to be truly invasive (unless the infant is markedly leukopenic). In such cases, the organism represents colonization of the respiratory tract and not infection.

Culture from other respiratory sites

In certain situations, culture of pleural fluid, bronchoscopic alveolar lavage fluid, nonbronchoscopic protected specimen brush samples, or specimens obtained by lung puncture may be valuable.

Culture from extrapulmonary lesions

Detection of microorganisms at inflamed extrapulmonary sites may be helpful because concurrent involvement of the lungs is not rare. Studies of abscesses, conjunctivitis, skin lesions, and vesicles may be fruitful.

Take care to ensure that the specimen submitted is as free of contamination as possible. Tests such as organism-specific DNA probe or polymerase chain reaction (PCR)–based assay are less likely to be affected by such factors.

Urine culture

During the first 3 days of life, urine culture is unlikely to be helpful because most urinary tract infections at this age are hematogenous.

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Serologic Tests

Serologic tests have limited use but may offer some insights in congenital pneumonia secondary to cytomegalovirus or toxoplasmosis. Serologic tests for syphilis may suggest or confirm the presence of pneumonia alba, particularly in high-risk populations.

Giacoia and colleagues espoused the value of assessing antibody responses in acute and convalescent sera from infants using flora recovered from endotracheal aspirates. [29] This usually permits diagnosis only retrospectively, but may be useful in infants who fail to adequately respond to empiric therapy or for epidemiologic purposes. Concerns persist regarding the specificity of such tests in distinguishing invasion from colonization.

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Markers of Inflammation

The use of markers of inflammation to support a diagnosis of suspected infection, including pneumonia, remains controversial.

Various indices derived from differential leukocyte counts have been used most widely for this purpose, although noninfectious causes of such abnormal results are numerous. Many reports have been published regarding infants with proven infection who initially had neutrophil indices within reference ranges.

Quantitative measurements of C-reactive protein, procalcitonin, cytokines (eg, interleukin-6), interalpha inhibitor proteins, [30] and batteries of acute-phase reactants have been touted to be more specific but are limited by suboptimal positive predictive value. There is a lag time from infection to the development of abnormal values. Serial measurements are often necessary, but do offer a high negative predictive value.

These tests may be useful in assessing the resolution of an inflammatory process, including infection, but they are not sufficiently precise to establish a diagnosis without additional supporting information. Decisions about antimicrobial therapy should not be based on inflammatory markers alone.

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Thoracentesis

In neonates with radiographically visible pleural fluid, careful positioning of the infant and thoracentesis after sterile preparation of the sampling site may provide specimens that yield diagnostic findings on Gram stain, direct microscopy, and/or culture. Ultrasonography may reveal smaller fluid pockets and facilitate safer sampling under direct visualization. Although data from studies in neonates are insufficient to draw conclusions, studies in older populations suggest a very high correlation with culture of lung tissue and blood.

The risk of pneumothorax or laceration of intercostal vessels is real but can be minimized by the use of proper technique, including use of the Z-technique (stretching the skin down over the entry site, so that release after the procedure will permit the return of tissues to their usual location with occlusion of the path of the needle), entry over the superior rib margin (to minimize inadvertent puncture of intercostal vessels) at a dependent site where fluid is most likely to collect, continuous aspiration once the skin is penetrated, and no further advancement once fluid is obtained. Sonographic guidance may facilitate performance.

This procedure may be therapeutic as well as diagnostic if the pleural fluid is impinging on lung or cardiac function.

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Bronchoscopy

Transbronchial biopsy and guided aspiration or brush specimens obtained via direct bronchoscopy may be advantageous in some circumstances. [31] Direct rigid bronchoscopy may be used in larger infants; fiberoptic technique is occasionally possible in smaller infants or infants in whom the site is not easily reached using the rigid technique. Both this technique and protected brush tracheal aspirate sampling may not be well tolerated in infants with significant lung disease and poor gas exchange who are very dependent on continuous positive pressure ventilation.

Quantitative culture of bronchoscopic alveolar lavage fluid has been assessed in non-neonatal populations and reported to offer a specificity of greater than 80%, depending on the threshold selected (values from >100 to 100,000 cfu/mL have been used). [32, 33] Data from studies of neonates with suspected congenital pneumonia are lacking.

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Protected Brush Tracheal Aspirate Sampling

Nonbronchoscopic protected specimen brush can be used to obtain culture material through endotracheal tubes 3 mm or greater in internal diameter. [34] Specimens may have an increased risk of contamination with oral or airway commensals compared with bronchoscopic sampling but are thought to be more accurate than a conventional endotracheal aspirate.

Data from neonates are sparse at present. Unlike bronchoscopically obtained specimens, ensuring sampling from a particular involved site is more difficult. Sites distant from the larger bronchi often cannot be sampled.

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Lung Aspiration

If a prominent infiltrate can be adequately localized in multiple planes, direct aspiration of the infected lung may be performed for culture or biopsy. [35] Lung CT may facilitate such localization.

Lung aspiration usually requires a larger-bore needle than is used to obtain pleural fluid and is associated with a greater risk of postprocedural air leak than thoracentesis.

Lung aspiration is used much less frequently than in previous decades. This is a high-risk procedure, with potential complications that include pneumothorax, bronchopleural fistula, hemothorax, and sampling a nondiagnostic site.

Lung aspiration should not be considered a routine aspect of the diagnosis or treatment of pneumonia in the neonate. Rather, this technique is usually reserved for circumstances in which empiric therapy is failing, less invasive cultures and detection tests are unrewarding, and/or the infant continues to deteriorate. With advances in surgical techniques and increased experience, many clinicians prefer to seek open surgical biopsy or thoracoscopic sampling in such circumstances, especially because success and specimen size are greater and the ability to deal directly with any complication is enhanced.

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Histologic Findings

Tissue samples of lung tissue in human infants have typically been obtained from an unrepresentative population. The sample population usually includes only infants with severe pulmonary disease that results in death or threatens to do so or infants who die of other causes and have coincidental sampling of the lung.

Consequently, direct observations regarding histologic changes in mild or moderate pneumonia are sparse and are often supplemented by extrapolation from animal disease models, human adults with similar diseases, or more severe cases in human infants that resulted in death or biopsy. Despite these limitations, certain observations in congenital pneumonia recur, whether or not a specific pathogen is implicated. [36]

Macroscopically, the lung may have diffuse, multifocal, or very localized involvement with visibly increased density and decreased aeration. Frankly hemorrhagic areas and petechiae on pleural and intraparenchymal surfaces are common. Airway and intraparenchymal secretions may range from thin and watery to serosanguineous to frankly purulent and frequently are accompanied by small-to-moderate pleural effusions that display variable concentrations of inflammatory cells, protein, and glucose.

Frank empyema and abscesses are unusual in newborn infants. Particulate meconium or vernix may be visible, especially in the more proximal airways, following aspiration episodes. Superimposed changes, such as air leak, emphysema, and sloughed airway mucosa, may be seen as a consequence of volutrauma, pressure-related injury, oxygen toxicity, and other processes that reflect the vigorous respiratory support often provided to these infants in an attempt to manage derangements of gas exchange caused by the underlying illness.

With conventional microscopy, inflammatory cells are particularly prominent in alveoli and airways. Mononuclear cells (macrophages, natural killer cells, small lymphocytes) are usually noted early, and granulocytes (eosinophils, neutrophils) typically become more prominent later. Microorganisms of variable viability or particulate debris may be observed within these cells. If systemic neutropenia is present, the number of inflammatory cells may be reduced. Alveoli may be atelectatic from surfactant destruction or dysfunction, partially expanded with proteinaceous debris (often resembling hyaline membranes), or hyperexpanded secondary to partial airway obstruction from inflammatory debris or meconium.

Microscopic examination of tissue following immunohistochemical staining or other molecular biologic techniques can identify the herpes virus and an increasing number of other organisms.

Hemorrhage in the alveoli and in distal airways is frequent. Vascular congestion is common; vasculitis and perivascular hemorrhage are seen less frequently. Inflammatory changes in interstitial tissues are less common in newborns than in older individuals.

Examination of the placenta may be useful. An unusually large placenta with a thick umbilical cord or necrotizing funisitis is suggestive of congenital syphilis, with an increased risk of congenital pneumonia alba. Although results of early maternal serologic screening may have been negative, false-negative results from the prozone phenomenon or infection later in pregnancy may occur. Careful microscopic examination for trophozoites may establish a diagnosis of congenital toxoplasmosis long before other confirmatory tests become available. Other evidence of inflammation or infection derived from gross inspection, microscopy, or specific microbiologic testing may also be useful.

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