Approach Considerations
Detection of adenovirus is most practical, cost-efficient, and desirable in the setting of epidemics and immunosuppressed populations, in which the diagnosis impacts public health and decisions to treat with antivirals.
All specimens are best collected within 1 week of symptom onset for optimal yield.
Laboratory Studies
Culture
Adenovirus is stable in routine viral transport medium. Appropriate samples include nasopharyngeal swabs or aspirates, throat swabs or washes, sputum, tracheal aspirates, bronchoalveolar lavage (BAL) fluid, conjunctival swabs or scrapings, stool or rectal swabs, urine, blood, cerebrospinal fluid (CSF), and unfixed tissue samples. Culture of viruses is not practical nor readily available in many hospital and some commercial laboratories, having been supplanted by antigen and polymerase chain reaction (PCR) assays.
Detection is enhanced if specimens are collected early in the clinical course and promptly shipped cold or frozen to the appropriate laboratory. Many adenovirus serotypes can be isolated in cell culture lines commonly used in diagnostic virology laboratories; a few, such as types 40 and 41, fail to grow (“noncultivatable” serotypes). Primary human embryonic kidney cells support growth of many fastidious adenovirus serotypes, but their additional cost may be prohibitive in some settings. Other cell lines may not support the growth of ocular strains well, may be less sensitive, or may not be maintainable to support slower-growing strains.
Serology
Seroreactivity to adenovirus is common. As a result, serology is available through commercial laboratories, but is less useful in the acute clinical setting. By age 4 years, approximately half of all children have positive adenovirus titers. If a serologic diagnosis is pursued, serum should be obtained as early as possible in the clinical course, followed by a second titer 2-4 weeks later. A 4-fold rise in acute titers to convalescent titers is diagnostic.
Antigen tests
Adenoviral antigen assays include direct fluorescent antigen (DFA) and enzyme immunoassay (EIA), and are available via commercial laboratories. Typical applications for antigen assays is in the diagnosis of epidemic keratoconjunctivitis, adenoviral respiratory disease, pharyngo-conjunctivitis, and enteritis. Antigen assays are the test of choice for the detection of the fastidious adenovirus types 40 and 41 in stool samples. These enteric adenoviruses are generally “noncultivatable” and an important cause of diarrhea in infants.
Indirect immunofluorescence assays may be used for direct examination of tissue specimens and are available through commercial laboratories
Polymerase chain reaction
Polymerase chain reaction (PCR) is being used with high specificity on various specimens (eg, respiratory, tissue, urine, blood) to identify adenovirus and is available through commercial laboratories. Common adenoviral serotypes are included in commercial respiratory viral PCR arrays. A positive result from upper respiratory tract or stool samples is more difficult to interpret as it may represent virus shedding rather than symptomatic infection. Therefore, PCR results must be interpreted in the context of pre-test probability and the clinical findings of adenovirus disease.
Detection of adenovirus DNA in the blood by quantitative PCR is increasingly utilized for the evaluation of adenovirus infections in immunocompromised patients. Studies have demonstrated an association between rising or high-level viremia and the risk of both invasive disease and mortality. [5, 28] [29]
Serotyping
Serotyping is generally in the domain of epidemiology and research and is not typically used in clinical practice. However, as specific syndromes are associated with specific serotypes, tests can be performed in a reference laboratory.Serotyping is available via Submitting Specimens to CDC | Infectious Diseases Laboratories | CDC.
Certain serotypes of enteric adenovirus have been seen in stool specimens using electron microscopy, but they have been difficult to isolate in routine tissue culture. These “noncultivatable” enteric adenoviruses are best detected by antigen assay. Adenovirus has been identified using electron microscopy and immunohistochemistry techniques. The isolation of enteric adenovirus infection in recipients of small bowel transplants in whom allograft damage is a risk may warrant stool cultures, antigen assays, or biopsy.
Transmission electron micrograph of adenovirus. Image courtesy of the US Centers for Disease Control and Prevention.
Syndrome-specific testing
The following laboratory studies are suggested in the given syndromes, both to diagnose adenoviral infections and to evaluate for other diagnoses in the differential diagnoses of each syndrome.
Acute respiratory disease
Nasopharyngeal swab for culture of respiratory viruses (eg, influenza virus, adenovirus, respiratory syncytial virus, rhinovirus) is suggested.
Consider Monospot assay for Epstein-Barr virus.
Consider rapid group A Streptococcus throat swab and culture.
Pharyngoconjunctival fever
Nasopharyngeal swab for culture or PCR of respiratory viruses (eg, influenza virus, adenovirus) is suggested.
Consider Monospot assay.
Consider rapid group A Streptococcus throat swab and culture.
Epidemic keratoconjunctivitis
Viral and bacterial swab cultures of conjunctival secretions and scrapings are suggested. It is best to obtain conjunctival swabs for both viral culture and adenovirus-specific ELISA or polymerase chain reaction (PCR) assay to make a diagnosis of EKC, since subgroup D isolates, which are frequently implicated, can take two to four weeks to grow in tissue culture.
Acute hemorrhagic cystitis or nephritis
Urinalysis and cultures for bacterial and viral pathogens are suggested.
Gastroenteritis
Consider stool Wright stain; ova and parasites examination; culture for bacterial enteric pathogens; assays for norovirus, rotavirus, and Cyclospora; and Clostridium difficile toxin assay.
In immunocompromised hosts, early identification of patients at risk for adenovirus disease by monitoring for viremia by PCR is beneficial; thus, some centers have adopted routine weekly surveillance measures for pediatric recipients of allogeneic hematopoietic stem cell transplants. If viremia is detected, then patients should be carefully evaluated for evidence of disease. Although viremia is self-limited in some patients, a rising viral load has been associated with invasive disease. [30]
Imaging Studies
Pneumonia
Plain radiography or CT scanning demonstrates typically diffuse and reticulonodular infiltrates. High-resolution CT scanning may show "crazy-paving" patterns in immunocompromised patients. [31] Occasionally, findings are lobar.
Hepatitis
Liver ultrasonography may be helpful to exclude obstructive causes of transaminitis or hyperbilirubinemia.
Nephritis
Renal ultrasonography is helpful to exclude obstructive causes of renal insufficiency or renal swelling that may indicate infection.
Other Tests
Urine cytology
Urine cytology should be considered to exclude other causes if hemorrhagic cystitis does not resolve within 5 days.
Procedures
Biopsy
Biopsy may be considered in the setting of pneumonia, hepatitis, nephritis, enteritis, or other suspected end-organ involvement in immunocompromised patients, particularly in transplant recipients.
Histologic Findings
Pneumonia
Obliterative bronchiolitis is seen; viral intranuclear and intracytoplasmic inclusions with positive immunohistochemical staining specific for adenovirus are noted. The intranuclear inclusions during late infection are surrounded by a clear halo, which may obstruct visualization of the nuclear membrane, resulting in a smudged appearance. These "smudged" cells are classically seen in adenovirus infection.
Enteritis
Denudation of the gastrointestinal mucosa with edema may be seen. Also, acute and chronic inflammatory infiltrate involving the full thickness of the bowel wall may be noted. Viral intranuclear and intracytoplasmic inclusions with positive immunohistochemical staining specific for adenovirus are noted within infected cells.
Hepatitis
Viral intranuclear and intracytoplasmic inclusions with positive immunohistochemical staining specific for adenovirus are noted within infected cells.
Nephritis
Viral intranuclear and intracytoplasmic inclusions with positive immunohistochemical staining specific for adenovirus are noted within infected cells. Tubular epithelium is typically involved until late; extension may occur thereafter to the Bowman capsule and the glomerulus.
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A virus image from the International Committee on Taxonomy of Viruses, in The Big Picture Book of Viruses, available at http://www.virology.net/Big_Virology/BVDNAadeno.html.
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Transmission electron micrograph of adenovirus. Image courtesy of the US Centers for Disease Control and Prevention.
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Pseudomembranes and conjunctival inflammation due to adenovirus epidemic keratoconjunctivitis. Courtesy of Steve Tuft, Moorfields Eye Hospital, and Community Eye Health Journal.
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Subepithelial infiltrates characteristic of adenoviral keratoconjunctivitis. Courtesy of Wikimedia Commons (author Imrankabirhossain).
