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| EPIDEMIOLOGY |
Parvovirus B19 infection is common and occurs world wide.
The disease is not notifiable in the UK and surveillance relies on
laboratory-confirmed cases. These show a 3-4 year epidemic cycle with a
seasonal peak in the first half of each year. Recent epidemic years have
been 1989-1990, 1993-1994 and 1997- 1998.
Infection is most common in children aged 6-10 years, but can
occur at any age. Antibody prevalence studies have shown that
approximately 60 per cent of adults in the UK have serological evidence
of past infection with parvovirus B19. One attack is thought to confer
lifelong immunity.
Respiratory secretions are involved in transmission. In human
volunteers, serum and respiratory secretions become positive for B19 DNA
5-10 days after intranasal inoculation. The virus is transmitted
effectively after close contact. Patients with TAC have an intense
viraemia and are highly infectious. The virus can also be transmitted
parenterally by some blood products (but not intramuscular
immunoglobulins) and vertically from mother to fetus. Faecal-oral
transmission has not been documented.
| INCUBATION |
For clinical cases the incubation period is 13-18 days, but can be as long as 20 days. Once the rash is present, the subject is no longer infectious.
| PREVENTION AND TREATMENT |
Immunisation and control policies
There is no vaccine available for the prevention of parvovirus
B19 infection, although a recombinant preparation is at an early
stage of development. The value of post-exposure prophylaxis with
normal immunoglobulin has not been assessed. There are no clear
guidelines at present on the control of parvovirus Bl9 infection.
For most individuals, parvovirus B19 infection causes a
mild, self-limiting illness and no intervention is required. Some
of the management approaches that have been adopted in other situations
are described below.
Outbreaks
in the home, school and the workplace
When outbreaks of parvovirus B19 infection occur in environments
where close contact occurs (e.g. at home or in day care centres),
options for preventing transmission are limited. This is because
the greatest risk of transmission occurs before the rash appears.
Identification and exclusion of those with symptoms cannot therefore
prevent spread in parvovirus B19 outbreaks. The efficacy
of decontaminating toys and environmental surfaces has not been
studied. In the USA, the
Centers for Disease Control (CDC) have recommended hand washing
as a simple procedure that may reduce the risk of transmission.
When outbreaks occur in schools or in the workplace, parents and
employees should be advised of the risks both of transmitting and
acquiring infection, and about the groups of people at risk of serious
complications. The decision to avoid a school environment or workplace
should be made by the individual after discussion and advice from
his or her family members, general practitioner, occupational or
public health doctor and employer.
Hospital outbreaks
In hospital outbreaks, strategies for limiting spread have centred
upon reducing the risk of infection in people in high-risk groups,
such as susceptible persons with haematological diseases or immunodeficiency,
and susceptible pregnant woman. Normal immunoglobulin has been given
prophylactically to high-risk patients in one hospital outbreak
but its efficacy was not assessed.
Other control measures that have been used include respiratory isolation of patients with TAC or chronic infection, exclusion of susceptible pregnant staff, patients and visitors from affected wards, testing of healthcare workers and allowing only B19 IgG positive staff to care for high-risk patients.
An investigation of a nosocomial outbreak of parvovirus B19 in 1992 by the PHLS suggested that rigorous hand-washing procedures could be effective in limiting the spread of infection.
Pregnancy
Pregnant women should be given information about parvovirus
B19, and those who have had recent exposure should have access
to advice and serological tests. Blanket decisions on exclusions
from work or transfer to a lower-risk area are not appropriate.
Serial fetal ultrasound is used for the diagnosis of hydrops fetalis. Intrauterine fetal transfusion, which requires specialist clinical
expertise, is used for the treatment of hydrops fetalis in some
centres and has been shown to improve survival. The specific management
of gestational parvovirus B19 infection in individual cases
is arrived at after consultation between the mother and her obstetrician. There is no indication for therapeutic termination of pregnancy
or routine antenatal screening for maternal parvovirus B19
infection.
Treatment
For most individuals, no specific treatment is required for
parvovirus B19 infection. Severe symptoms and complications
may require appropriate measures. Joint pain may require analgesia,
and severe anaemia in immunodeficient or haematological patients
may require blood transfusion. Intravenous normal immunoglobulin
has been successfully used in the treatment of chronic infection
in immunodeficient patients.