Disinfection and disinfectants WORLD OF MICROBIOLOGY AND IMMUNOLOGY158•
form of diphtheria, causing the characteristic throat mem-
brane. The membrane often bleeds if it is scraped or cut. It is
important not to try to remove the membrane because the
trauma may increase the body’s absorption of the exotoxin.
Other signs and symptoms of pharyngeal diphtheria include
mild sore throat, fever of 101–102°F (38.3–38.9°C), a rapid
pulse, and general body weakness.
Laryngeal diphtheria, which involves the voice box or
larynx, is the form most likely to produce serious complica-
tions. The fever is usually higher in this form of diphtheria
(103–104°F or 39.4–40°C) and the patient is very weak.
Patients may have a severe cough, have difficulty breathing, or
lose their voice completely. The development of a “bull neck”
indicates a high level of exotoxin in the bloodstream.
Obstruction of the airway may result in respiratory compro-
mise and death.
The skin form of diphtheria, which is sometimes called
cutaneous diphtheria, accounts for about 33% of diphtheria
cases. It is found chiefly among people with poor hygiene.
Any break in the skin can become infected with diphtheria.
The infected tissue develops an ulcerated area and a diphthe-
ria membrane may form over the wound but is not always
present. The wound or ulcer is slow to heal and may be numb
or insensitive when touched.
The diagnosis of diphtheria can be confirmed by the
results of a cultureobtained from the infected area. Material
from the swab is put on a microscopeslide and stained using
a procedure called Gram’s stain. The diphtheria bacillus is
called Gram-positive because it holds the dye after the slide is
rinsed with alcohol. Under the microscope, diphtheria bacilli
look like beaded rod-shaped cells, grouped in patterns that
resemble Chinese characters. Another laboratory test involves
growing the diphtheria bacillus on Loeffler’s medium.
The most important treatment is prompt administration
of diphtheria antitoxin. The antitoxin is made from horse
serum and works by neutralizing any circulating exotoxin. The
physician must first test the patient for sensitivity to animal
serum. Patients who are sensitive (about 10%) must be desen-
sitized with diluted antitoxin, since the antitoxin is the only
specific substance that will counteract diphtheria exotoxin. No
human antitoxin is available for the treatment of diphtheria.
Antibioticsare given to wipe out the bacteria, to prevent
the spread of the disease, and to protect the patient from devel-
oping pneumonia. They are not a substitute for treatment with
antitoxin. Both adults and children may be given penicillin,
ampicillin, or erythromycin. Erythromycin appears to be more
effective than penicillin in treating people who are carriers
because of better penetration into the infected area. Cutaneous
diphtheria is usually treated by cleansing the wound thor-
oughly with soap and water, and giving the patient antibiotics
for 10 days.
Universal immunization is the most effective means of
preventing diphtheria. The standard course of immunization
for healthy children is three doses of DPT (diphtheria-tetanus-
pertussis) preparation given between two months and six
months of age, with booster doses given at 18 months and at
entry into school. Adults should be immunized at 10-year
intervals with Td (tetanus-diphtheria) toxoid. A toxoid is abacterial toxin that is treated to make it harmless but still can
induce immunityto the disease.
Diphtheria patients must be isolated for one to seven days
or until two successive cultures show that they are no longer
contagious. Because diphtheria is highly contagious and has a
short incubation period, family members and other contacts of
diphtheria patients must be watched for symptoms and tested to
see if they are carriers. They are usually given antibiotics for
seven days and a booster shot of diphtheria/tetanus toxoid.
Reporting is necessary to track potential epidemics, to
help doctors identify the specific strain of diphtheria, and to
see if resistance to penicillin or erythromycin has developed.
In 1990, an outbreak of diphtheria began in Russia and spread
within four years to all of the newly independent states of the
former Soviet Union. By the time that the epidemic was con-
tained, over 150,000 cases and 5000 deaths were reported. A
vast public health immunization campaign largely confined
the epidemic by 1999.See alsoBacteria and bacterial infection; Epidemics, bacterial;
Public health, current issuesDIRECT MICROSCOPIC COUNT •see
LABORATORY TECHNIQUES IN MICROBIOLOGYDISEASE OUTBREAKS• seeEPIDEMICS AND PAN-
DEMICSDDisinfection and disinfectantsISINFECTION AND DISINFECTANTS
Disinfection and the use of chemical disinfectants is one key
strategy of infection control. Disinfection refers to the reduc-
tion in the number of living microorganismsto a level that is
considered to be safe for the particular environment.
Typically, this entails the destruction of those microbes that
are capable of causing disease.
Disinfection is different from sterilization, which is the
complete destruction of all microbial life on the surface or in
the liquid. The steam-heat technique of autoclaving is an
example of sterilization.
There are three levels of disinfection, with respect to
power of the disinfection. High-level disinfection will kill all
organisms, except for large concentrations of bacterial spores,
using a chemical agent that has been approved as a so-called
sterilant by the United States Food and Drug Administration.
Intermediate level disinfection is that which kills mycobacte-
ria, most viruses, and all types of bacteria. This type of disin-
fection uses a chemical agent that is approved as a
tuberculocide by the United States Environmental Protection
Agency (EPA). The last type of disinfection is called low-level
disinfection. In this type, some viruses and bacteria are killed
using a chemical compound designated by the EPA as a hos-
pital disinfectant.
There are a variety of disinfectants that can be used to
reduce the microbial load on a surface or in a solution. Thewomi_D 5/6/03 2:09 PM Page 158