EPIDEMIC
EPIGLOTTITIS
epidemic
A term applied to a disease
that for most of the time is rare in a
community but suddenly spreads rapid-
ly to affect a large number of people.
Epidemics of new strains of
influenza
are common. (See also
endemic.)
epidemiology
The branch of medicine
concerned with the occurrence and dis-
tribution of disease, including
infectious
diseases
and noninfectious diseases
such as cancer.
In epidemiological studies, the mem-
bers of a population are counted and
described in terms of such variables as
race, sex, age, social class, occupation,
and marital status. Then the
incidence
and
prevalence
of the disease of inter-
est are determined. These observations
may be repeated at regular intervals in
order to detect changes over time. The
result is a statistical record that may
reveal links between particular variables
and distribution of disease.
In comparative epidemiological stud-
ies, two or more groups are chosen. For
example, in a study of the link between
smoking and lung cancer, one group
may consist of smokers and the other of
nonsmokers; the proportion with cancer
in each group is calculated.
epidermis
The thin outermost layer of
the
skin.
epidermolysis
bullosa
A group
of
rare, inherited conditions, varying wide-
ly in severity, in which blisters appear
on the skin after minor injury or occur
spontaneously. The conditions can be
diagnosed by a skin
biopsy
. There is no
specific treatment. The outlook varies
from
gradual
improvement in
mild
cases to progressive serious disease in
the most severe cases.
epididymal cyst
A harmless swelling,
usually painless, that develops in the
epididymis.
Small cysts are common in
men over 40 and need no treatment.
Rarely, they become tender or enlarge
and cause discomfort, in which case
surgical removal may be necessary.
epididymis
A long, coiled tube that
runs along the back of the testis and
connects the vasa efferentia
(small
tubes leading from the testis) to the
vas
deferens
(the sperm duct leading to the
urethra). Sperm cells, which are pro-
EPIDIDYMIS
duced in the
testis
, mature as they pass
slowly along the epididymis and are
then stored in the
seminal vesicles
until
ejaculation
takes place.
Disorders of the epididymis include
epididymo-orchitis
and
epididymal cysts
.
Infection or injury can block the epidi-
dymis, which, if both testes are affected,
may result in
infertility
.
epididymitis
See
epididymo-orchitis
.
epididymo-orchitis
Acute
inflamma-
tion of a
testis
along with its associated
epididymis
. Epididymo-orchitis causes
severe pain and swelling at the back of
the testis, and, in severe cases, swelling
and redness of the
scrotum
.
The inflammation is caused by infec-
tion. Often, there is no obvious source
of infection, but sometimes the cause is
a bacterial
urinary tract infection
that
has spread via the
vas deferens
to the
epididymis. Treatment is with
antibiotic
drugs
.
If there is an underlying urinary
tract infection, its cause will be investi-
gated. (See also orchitis.)
epidural
anaesthesia
A method of
pain relief in which a local anaesthetic
(see
anaesthetic, local
) is injected into
the epidural space (the space around
the membranes surrounding the spinal
cord) in the middle and lower back to
numb the nerves that supply the chest
and lower body. Epidural anaesthesia is
used to relieve pain during and after
surgery and during
childbirth
.
epiglottis
The flap of
cartilage
lying
behind the tongue and in front of the
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