Impetigo is a contagious bacterial infection of the very superficial layers of the skin.
It is the third most common skin infection in children, affecting primarily children ages two to six years, but it can occur in persons of all ages.
Contents
What
Causes Impetigo?
How do
you get Impetigo?
When
should I be concerned that I might have impetigo?
What
else can look like impetigo?
Prevention:
How is
impetigo diagnosed?
Impetigo
in the Era of Superbugs:
Treatment:
Can I
get impetigo again?
Complications:
Impetigo is a contagious bacterial infection of the very superficial layers
of the skin. It is the third most common skin infection in children, affecting
primarily children ages two to six years, but it can occur in persons of all
ages. Impetigo is very contagious, since large numbers of infectious bacteria
are on the surface of the skin and can easily spread to others either by direct
person-to-person contact of the infected area, or by indirect contact when the
bacteria wind up on contaminated surfaces or objects.
This is especially a problem within families, in daycare centers, preschools,
and school classes.
What Causes Impetigo?
Impetigo is caused by two types of
bacteria. Virtually all cases in non-tropical climates are due toStaphylococcus
aureus (hereafter called “Staph”). In the tropics, Streptococcus
pyogenes (hereafter called “Strep”) is the most common
cause. In some patients both types of bacteria can be found. Since
Staph is increasingly resistant to commonly used antibiotics,
taking a bacterial culture may be an important part of evaluating a patient
with impetigo.
How do you get Impetigo?
Humans are the only carriers of Staph so
cases spread from one infected person to another, either directly or
indirectly. Humans carry Staph in the front part of their nose where the hair
is. This “carriage” can be asymptomatic. Carriage of Staph is very common with
10% to 20% of the population carrying Staph at any one time. Certain “risks”
increase the likelihood that people will be Staph “carriers.” Staph carriage is
increased in persons who get injections (allergy shots, insulin shots), in
persons who work in healthcare, and in persons with diseased skin, especially
eczema. HIV infection also increases the rate of Staph carriage.
Persons who carry Staph in their nose are at particular risk to get Staph impetigo.
Because people rub their noses regularly, the majority of persons who are Staph
carriers also have Staph on their hands. If they scratch their skin due to a
rash or irritation, they will inoculate the Staph onto that site. If an adult
or child who is a Staph carrier touches a person with broken skin, they could
inoculate Staph into that wound, resulting in a skin infection. This is how
Staph impetigo is spread in homes, schools and hospitals. Bacteria can live for
a while under scabs or crusts, which prevent them from being washed off the
surface. Picking at infected scabs of impetigo or infected skin rashes put
bacteria onto the hands. If these hands touch another area of that person’s
skin or another person, they could spread the impetigo.
Humans
can carry Strep asymptomatically in their throats, which can be the source of
spread to others. Strep can also be carried by dogs, so pets can be
the source of Strep-caused impetigo. Dogs with rashes or mange in the tropics
can be the source of impetigo and contact with dogs with rashes in the tropics
should be avoided. Houseflies in the tropics often land and feed on the Strep
in lesions of impetigo, and can be a way the bacteria are spread from person to
person.
Normal
skin usually prevents the bacteria causing impetigo from producing
infection. Healthy skin contains tiny molecules which kill bacteria.
They are called “antimicrobial peptides.” They are secreted onto the surface of
the skin in the oil layer that is present. Most cases of impetigo in healthy
persons occur when this normal skin barrier is “broken” by some minor trauma.
Scratching bug bites or other rashes in children and shaving the face or legs
in adults are the most common types of minor trauma that break the skin barrier.
Allergic rashes like eczema block the production of the normal “antimicrobial
peptides” creating the combination of broken skin and lack of local defense
which allows the bacteria to establish an infection.
Impetigo typically starts as a small bump
or pimple, often on skin that has been inflamed or broken. Once the bacteria
have broken through the person’s skin immune barrier, they begin to multiply
and spread across the skin surface. The bacteria secrete special chemicals that
do two things: 1) block the person’s local immune system, and 2) break apart
the skin to make it easier for the bacteria to get in. They can be spread to
other sites on the person by picking and scratching. Individual spots of
impetigo progress over one to a few days to a honey-colored crust, which may
become as big as two centimeters (about one inch) in diameter. This form of
impetigo is called non-bullous or non-blistering impetigo. It is the most
common form and can be due to either Staph or Strep. It usually affects exposed
areas such as the face, arms, or legs. It can spread on the body from the
initial affected area to other areas, especially the folds of the groin and the
armpits. Bug bites commonly become infected with Strep in the tropics, forming
lesions of impetigo.
Bullous or blistering impetigo is always
caused by Staph. It also starts as a small bump, but rapidly forms a blister,
usually about 5-7 mm (¼ to 1/3 inch) in diameter. This blister fluid is
initially clear, but may become cloudy. The blisters break after 1-2 days and
form a honey colored crusted lesion, sometimes with a rim of blister around the
border. Only some Staph strains can cause bullous impetigo. To cause these
blisters, the bacteria must produce a specific toxin that breaks the glue that
holds the skin cells together.
Secondary impetigo (impetiginization):
If the skin is damaged by an injury or a
rash (especially atopic dermatitis or eczema), Staph or Strep can enter this
damaged skin and cause an infection. This is called as “secondary” infection,
since the injury or rash is the primary process. Dermatologists use the term
Secondary impetigo or “impetiginization” to describe this infection of damaged
skin. Secondary impetigo is one of the most common reasons a child with eczema
gets a bad flare-up of their eczema.
When should I be concerned that I might have impetigo?
Any inflamed area of the skin that
develops a crust or scab could represent impetigo. Impetigo is more likely if
the spot started as a blister, or if the area forms a honey-colored crust. If
spots appear at other sites, that could represent impetigo due to its
contagion. If other persons in a living situation develop spots, that could
suggest impetigo. Persons with diseased skin, especially eczema should be
particularly concerned that their eczema has impetiginized. In
persons with eczema, the formation of a crack where the earlobe attaches to the
neck is a sign that Staph is causing a problem. A flare of the eczema or
increased crusting of the surface of the eczema can all suggest impetigo.
What else can look like impetigo?
Not every crusted spot on the skin is
impetigo. The most common condition that is mistaken for impetigo is a local
area of skin allergy (allergic contact dermatitis). Poison
ivy and oak, topical antibiotics (especially neomycin and bacitracin), vitamin
E, and many other things can cause local areas of itchy, crusted skin. This
kind of allergy can be very hard to distinguish from impetigo, and many cases
are inappropriately treated with antibiotics because the diagnosis of allergic
dermatitis is not thought of. The features that favor the diagnosis of allergic
dermatitis are a lot of itching and the shape of the affected area. These
allergic rashes tend to come in straight lines (poison ivy and oak) or exactly
in the pattern in which the topical preparation was applied (usually a nice
round circle). Fever blisters or cold sores due to
herpes simplex also get crusted as they heal, and can look a lot like impetigo.
The diagnosis of herpes simplex is favored if the person has a history of cold
sores in that area, if there was tingling before the skin inflammation
appeared, and if the spot started as a group of small blisters. The skin
lesions of chickenpox or varicella heal as crusted
areas, but start as tiny blisters, not crusts. The blisters of chickenpox are a
bit smaller than those of impetigo and sit on top of a red area of skin
(described as a dewdrop on a rose petal). Chickenpox is usually widespread and
associated with fever and sores in the mouth (a location where impetigo doesn’t
appear). Bug bites from bed bugs, lice, scabies, and
other biting insects begin as red raised itchy bumps. As they progress, they
can form crusting, especially if they are scratched. At times this crusting may
represent impetigo, but at times can be the normal healing phase of the bite.
Other skin rashes that can be crusty and confused with impetigo include atopic
dermatitis (childhood eczema), ringworm on the body or scalp; bad scalp
dandruff, and even the early skin lesions of shingles.
Prevention of impetigo involves several
approaches. For all forms of impetigo the affected person should not share
towels or personal items with others. Hand washing in the house, schoolroom, or
healthcare facility is critical to prevent the spread. Alcohol gels or soap and
water are recommended. If there is an outbreak in a school, toys and surfaces
should be cleaned with antimicrobials such as bleach. Persons who have eczema
must be particularly careful to avoid acquiring these infections. Soaking for
15 minutes in a “bleach bath” with ½ to 1 cup of household chlorine bleach in a
tub with 20 liters (5 gallons) of water, can be very effective in keeping
eczematous skin from becoming infected by bacteria. Staph is most commonly
carried in the front part of the nose (where the hairs are). The groin, vagina,
and armpits are other areas where Staph can be carried without generating any
lesions, but be a source for impetigo. Carriage at the nose and other sites is
common. Standard antibiotics treatments do not eradicate carriage, so specific
treatment for this “nasal carriage” may be required if a person suffers from
recurrent episodes of impetigo. Topical mupirocin and oral rifampin or
clindamycin can be used to eradicate carriage of Staph. Rifampin and
clindamycin can also eradicate Strep carriage.
The diagnosis of impetigo is usually made
by looking at the skin. If a blister is present (bullous impetigo), the blister
fluid can be put on a slide and stained for bacteria with a Gram stain.
This is quick and can sometimes be done in a doctor’s office or clinic. The
standard way to diagnose impetigo is to perform a bacterial culture.
This is obtained by swabbing the surface of the skin. If a blister is present,
the blister is broken and a sample of the blister fluid is collected on a swab
and submitted to the laboratory. A bacterial culture takes 24-48 hours. After
one day the laboratory can tell whether specific infectious bacteria are
present (Staph or Strep). Another day is required to tell what antibiotics will
kill the bacteria (this is called “sensitivity” testing). If the diagnosis of
impetigo is being considered and a Gram stain can’t be done, the patient and
healthcare provider can choose one of three options: 1) Culture the lesion AND
treat for impetigo, 2) Culture the lesions and wait for the result of the
culture to decide if treatment is required, or 3) Treat for impetigo but do not
perform a bacterial culture. In the last case, laboratory tests are performed
if the skin does not heal. All of these approaches are acceptable, and the
choice is made based on several factors: the likelihood the correct diagnosis
is impetigo, the availability of laboratory services, community standards,
local rates and causes of impetigo, and certain features of the patient. If the
patient has a suppressed immune system, if the infection is recurrent, or if
the patient works with children or is in healthcare, a bacterial culture should
probably be performed.
Impetigo in the Era of Superbugs:
Staphylococcus has always been known to be
capable of developing resistance to antibiotics. Soon after penicillin began to
be used to treat infections, Staph but not Strep, developed resistance to
penicillin. Special semisynthetic penicillins were developed and for several
decades effectively treated most Staph infections. Within the last decade, more
resistant Staph strains began to appear, first in hospitals, and over the last
few years in the general community. These Staph strains are resistant to the
semisynthetic penicillins and are called MRSA, or methicillin resistant S.
aureus. They now represent a significant proportion of the strains of Staph
causing skin infections both in patients in hospitals and in the community.
These MRSA strains have created a major healthcare problem. Not only are
infections by these bacteria resistant to antibiotics, but they also are more
aggressive than the previously common Staph strains. While the superficial
infections due to these superbugs do not look different from regular impetigo,
impetigo caused by these MRSA strains is more likely to progress to a deeper
and more serious infection, such as cellulitis. Serious infections by these
MRSA strains are more likely to require hospitalization. For all of these
reasons, identifying and eradicating superficial infections caused by these
“superbugs” is critical. In communities where MRSA, is common, bacterial
cultures and sensitivity testing may be required to choose the optimal
antibiotic to treat the impetigo. If an MRSA strain is isolated from a
superficial skin infection, the treatment should be adequate to eradicate the
infection, and the patient should be followed to be sure the infection is
completely eliminated. Treatment of the person’s presumed nasal carriage of
this MRSA strain could be considered, especially if they work in a school, a
residential institution (prison, long-term care facility), or in healthcare.
Treatment for impetigo can be either with topical
agents or oral antibiotics. Topical treatment (the application of
creams to the infection) is only recommended if the area of infection is
limited to one or two places, AND the infected person has a normal immune
system and normal skin. Cleansing the area with soap and water to remove the
crust may be helpful. At times there are collections of pus and bacteria below
the crusts and uncovering these may accelerate healing. Everyone who has
eczema, atopic dermatitis, or a compromised (reduced) immune system should be
treated with oral antibiotics.
Topical
Treatment: For small areas of impetigo, topical mupirocin,
fusidic acid (not available in the USA), or less ideally, topical bacitracin or
neomycin can be used. Allergy to neomycin and bacitracin is common,
making these treatments less favored.
Oral
Antibiotics: In developed countries, the majority of patients with
impetigo are treated with oral antibiotics. This is largely because most cases
are due to Staph and it is harder to clear than Strep. First-line antibiotics
would be a first generation cephalosporin (Cephalexin/Keflex) or semisynthetic
penicillin (Dicloxacillin/Dynapen). These antibiotics are cheap,
easy to take, safe, and highly effective. In generic form they are cheaper than
mupirocin topical treatment.
In
communities where antibiotic-resistant Staph, including MRSA, is common, a
bacterial culture may be more important in selecting the appropriate antibiotic
treatment for impetigo. For penicillin-allergic persons and for MRSA, a
combination of a sulfa drug and trimethoprim
(trimethoprim/sulfamethoxazole/Bactrim/Septra) or a tetracycline derivative
such as doxycycline can be effective. These antibiotics are economical and
available as generics. Treatment of superficial infections due to these MRSA
strains may be continued for longer periods to be sure the infection has been
eradicated. In addition, eradication of nasal carriage could be considered to
prevent recurrence in the affected patient or spread of the MRSA to another
person. Aggressive treatment for “carriage” could be considered for persons
working or living in institutions (prisons, long-term care facilities, etc) and
for persons who teach school or work in healthcare.
Impetigo can occur in the same person over
and over, if the underlying cause is not treated. The most common cause of a
second episode of impetigo in a healthy person is that they are a Staph carrier
and the Staph carriage has not been eradicated from their nose. Also, another
person in the home may be an asymptomatic Staph carrier and repeatedly
infecting others in the household, giving them impetigo. Persons
with eczema carry lots of Staph on their skin and may spread this to others, causing
secondary cases of impetigo in the home. To treat recurrent cases of impetigo,
the first step is to eradicate Staph from the nose—eradicate the nasal
carriage. This can be done with topical antibiotics such as mupirocin or with
special oral antibiotics such as rifampin or clindamycin. If this does not
prevent the impetigo from coming back, then others in the household should be
treated for nasal Staph carriage.
Rarely,
recurrent impetigo may be a sign of an impaired immune system. HIV infection,
and in the certain parts of the world HTLV-1 infection (caused by another
retrovirus related to HIV) can be found in persons who get recurrent Staph
impetigo. People with congenital deficiencies of the immune system
usually present with infections at a very young age. Extensive evaluations of
the immune system rarely reveal a cause for recurrent impetigo in older
children or adults.
Impetigo is so superficial in the skin
that it should heal without scarring. If the bacteria continue to multiply
on the surface of the skin, they can produce molecules that further damage the
skin’s resistance and can invade deeper into the skin. If they simply dig a
deeper hole in the skin, this is called ecthyma, and usually remains as a
chronic ulcer that doesn’t heal. If the infection penetrates down a hair
follicle, it can form a localized area of pus and infection, which is painful.
This is called an abscess or boils. If the infection goes through
the surface of the skin and begins to spread under the skin, it creates a red
tender area called a cellulitis. Cellulitis can spread rapidly through the skin
and may go into the blood stream causing “blood poisoning” or septicemia. These
more serious forms of Staph or Strep infection cannot be treated topically, and
require either oral antibiotics (ecthyma), intravenous antibiotics
(cellulitis), or surgical drainage (abscess or boil).
Streptococcal impetigo may be complicated
by kidney damage, if it is caused by certain, special strains of Strep. These
episodes of kidney disease may occur as “outbreaks” or “epidemics” of kidney
disease in a community. Kidney disease following Streptococcal impetigo is
caused by the person’s own immune system. The antibodies produced to kill the
Strep collect in the kidneys, causing them to fail. This form of kidney disease
presents with dark urine (due to blood in the urine) and retention of fluid
(weight gain and swelling of the hand, feet and face). It occurs 7-10 days
after the skin infection, lasts for several weeks to months, and usually goes
away without any specific
treatment. Treatment of the
Strep impetigo does not prevent the kidney disease. If these kidney-damaging
strains of Strep are causing impetigo in a community, aggressive treatment and
isolation of impetigo cases and public health measures can prevent new cases of
impetigo and more cases of kidney damage. As noted above, if dogs with skin
disease are felt to be carrying these kidney-damaging Strep strains, removing
these dogs from the community may be important.
