Case 5
1. Describe the modes of adenoviral transmission.
Adenoviruses causing respiratory tract infection usually are transmitted
by respiratory tract secretions through person-to-person contact, fomites,
and aerosols. Because adenoviruses are stable in the environment, fomites
may be important in their transmission. The conjunctiva can provide a portal
of entry. Community outbreaks of adenovirus-associated pharngonconjunctival
fever have been attributed to exposure to water from contaminated swimming
pools and fomites, such as shared towels. Epidemic keratoconjunctivitis
often has been associated with nosocomial transmission in ophthalmologists’
offices. Enteric strains of adenoviruses are transmitted by the fecal-oral
route. Nosocomial spread often has resulted from exposure to contaminated
hands of health care workers and infected equipment, including
pneumotonometers and opthalmologic solutions.
2. Describe the clinical manifestations of adenoviral infections.
The most common site of adenovirus infection is the upper respiratory
tract. Manifestations include symptoms of the common cold, pharyngitis,
pharyngoconjunctival fever, tonsillitis, otitis media, keratoconjunctivitis,
often associated with fever. Life-threatening disseminated infection, severe
pneumonia, meningitis, and encephalitis occasionally occur, especially among
young infants and immunocompromised hosts. Adenoviruses are infrequent
causes of acute hemorrhagic conjunctivitis, a pertussis-like syndrome,
croup, bronchiolitis, hemorrhagic cystitis, and genitourinary tract disease.
In children, the best described syndrome attributed to adenoviruses is
the so-called pharyngoconjunctival fever. This disease occurs in small
outbreaks and seen by physicians at children’s summer camps. It is
characterized by conjunctivitis, pharyngitis, rhinitis, cervical adenitis,
and temperatures to 380C. The onset is acute, and the fever and
other symptoms last 3-5 days. Bulbar and palpebral conjunctivitis may be the
only finding, and the palpebral conjunctivae usually have a granular
appearance.
A few adenovirus serotypes, types 40 and 41, have been associated with
gastroenteritis, and are responsible for about 4% of serious diarrhea in
infants and children.
The predominant cause of exudative tonsillitis in infants and toddlers is
of adenoviral etiology.
3. What is known about the pathogenesis of adenoviral infections?
The oropharyngeal and nasopharyngeal mucous membranes are the tissues
primarily affected early in acute infection.
Adenoviruses appear to be capable of at least three types of interaction
with cells.
1) The first is a lytic infection in which the virus goes through an
entire replicative cycle. Lytic infection occurs in human epithelial cells
and results in cell death and in the production of 10,000 – 1 million
progeny viruses per cell, of which 1-5 percent are infectious.
2) The second interaction is a latent or chronic infection. This usually
involves lymphoid cells. During latent infection, only small numbers of
viruses may be released, and cell death may be outstripped by cell
multiplication, thereby resulting in inapparent infection. The mechanisms
are not clearly established.
3) The third significant virus – cell interaction occurring with
adenoviruses is that of oncogenic transformation. In this situation, only
the early steps in virus replication occur. The viral DNA is apparently
integrated into and replicated with the cell’s DNA, but no infectious
virions are produced. In all three types of infection, virus-specific
proteins (T antigens) are synthesized. These antigens give evidence of
adenoviral presence even in the absence of infectious virus. The T antigens
are detected either by complement fixation or by immunofluorescence assays
using serum from hamsters bearing tumors induced by adenovirus.
4. What type of isolation should the patient be in while in the hospital?
For young children with respiratory tract infection, contact and droplets
precautions are indicated for the duration of hospitalization. For patients
with conjunctivitis, contact precautions in addition to standard precautions
are recommended. For diapered and incontinent children with adenoviral
gatroenteritis, contact precautions in addition to standard precautions are
indicated for the duration of the illness.
5. How is the viral infection detected?
Detection of adenovirus infection by culture or antigen is the preferred
diagnostic method.
Adenoviruses associated with respiratory tract disease can be isolated
from pharyngeal secretions, eye swabs, and feces by inoculation of specimens
into a variety of cell cultures. A pharyngeal isolate is more suggestive
of recent infection than is a fecal isolate, which may indicate either
prolonged carriage or recent infection.
Adenovirus antigens can be detected in body fluids of infected persons by
immunoassay techniques, which are especially useful for diagnosis of
diarrheal disease, because enteric adenovirus types 40 and 41 usually cannot
be isolated in standard cell cultures. Enteric adenoviruses also can be
identified by electron microscopy of stool specimens. Multiple methods to
detect group-reactive hexon antigens in body secretions and tissue have been
developed. Also, detection of viral DNA can be accomplished with genomic
probes, synthetic oligonucleotide probes, or gene amplification by
polymerase chain reaction. Serodiagnosis is based on detecting a 4-fold or
greater rise in antibodies to a common adenovirus antigen (eg, hexon).
Serodiagnosis is used primarily for epidemiologic studies.
6. Describe the measures for prevention of the spread of adenoviral
infection.
Adequate chlorination of swimming pools is recommended to prevent
pharyngoconjunctival fever. Epidemic keratoconjunctivitis associated with
ophthalmologic practice can be difficult to control and requires use of
single-dose medication dispensing and strict attention to hand washing and
instrument sterilization procedures. Effective disinfection can be
accomplished by immersion of contaminated equiment in a 1% solution of
sodium hypochlorite for 10 minutes or by steam autoclaving.
Health care personnel with known or suspected adenoviral conjunctivitis
should avoid direct patient contact for 14 days after the onset of disease
in their second eye. Because adenoviruses are particularly difficult to
eliminate from skin, fomites, and environmental surfaces, assiduous
adherence to hand washing and use of disposable gloves when caring for
infected patients are recommended.
Children who participate in group child care, particularly children from
6 months through 2 years of age, are at increased risk of adenoviral
respiratory tract infections and gastroenteritis. Measures for preventing
spread of adenovirus infection in this setting have not been determined, but
frequent hand-washing is recommended.