Airborne transmission involves infected microorganisms or dust particles that remain suspended in the air for long periods of time and can be dispersed widely by air currents. Depending on environmental factors, a susceptible host may inhale particles within the same room or over a longer distance from the source patient. Special air handling and ventilation are required to prevent airborne transmission. In addition to standard precautions, airborne precautions include patient placement in a negative pressure room, use of respiratory protection such as an N95 respirator, and limitation of patient transport.

Droplets can be transmitted from coughing, sneezing, and talking, and during certain procedures such as suctioning and bronchoscopy. Transmission is via the host’s conjunctivae, nasal mucosa, or mouth. Droplets do not remain suspended in the air and as such ventilation is not needed. Do not confuse droplet precautions with airborne transmission. In addition to standard precautions, droplet precautions include placement of the patient in a private room, use of a mask (especially when within 3 feet of the patient), and limited patient transport.

Contact is the most frequent mode of transmission of nosocomial infections and is divided into direct- and indirect-contact transmission.

Anthrax is a bacterial infection caused by Bacillus anthracis, an encapsulated, gram-positive, spore-forming bacterium. B. anthracis is present in both domestic and wild animals throughout the world and can be transmitted by their meat, wool, or hides. The spores are resistant to heat, UV light, microwave radiation, and many disinfectants. B. anthracis has been classified by the CDC as a category A bioterrorism agent because of its high lethality, hardiness, and ease of weaponization. In 2001 there were 22 cases of anthrax as a result of a bioterrorist attack. In 2002 the U.S. Department of Defense reintroduced the vaccination of military personnel and essential emergency civilians against anthrax.

There are three forms of anthrax:

Each is discussed separately on the following pages.

Although inhalational and gastrointestinal forms of anthrax exist, approximately 95% of all anthrax cases are cutaneous. Before 2001 there had not been a case of cutaneous anthrax reported in the United States since 1992. In the September 11, 2001 attacks, 11 of the 22 cases were cutaneous.

Cutaneous contact with aerosolized spores.

Cutaneous anthrax lesions evolve from pruritic papules to clusters of vesicles to ulcers within 1 to 2 days following exposure of abraded skin or wounds to the spores. The ulcers then develop into depressed black eschar over the next 2 to 5 days. The most common areas affected are the arms, face, and neck. Lymphangitis and painful lymphadenopathy are common.

With antibiotic treatment the death rate for cutaneous anthrax is approximately 1%. However, without treatment it may progress to a systemic form of anthrax with a death rate of approximately 20%. In these cases, the spores introduced into the body are eaten by macrophages and taken to regional lymph nodes, where they germinate into bacteria. Released into the lymph system, they enter the bloodstream, causing septicemia that results in a fatal toxemia.

See Table 6-3 for drug therapy.

Low risk to personal safety.

Standard precautions. Avoid direct contact with lesion(s) or lesion drainage.

Low: Cutaneous anthrax is not contagious.

Vaccine is available.

Gastrointestinal anthrax is rare; it is caused by consuming contaminated meat products and results in inflammation of the gastrointestinal (GI) tract.

For the purposes of biological warfare, GI anthrax would be placed in the food supply. Some countries have already experimented with this agent; both Japan and the former apartheid government of South Africa created anthrax-laced chocolates. The last reported case of GI anthrax in the United States was in 2000.

Contamination of food supply.

Symptoms of gastrointestinal anthrax include fever, anorexia, abdominal pain, ascites, bloody vomit, and diarrhea.

See Table 6-4 for drug therapy.

Low risk to personal safety.

Standard precautions.

Low: Gastrointestinal anthrax is not contagious.

Vaccine is available.

If anthrax were to be weaponized, the most likely method of dispersal would be by aerosol release, and although gastrointestinal and cutaneous forms of anthrax exist, inhalational anthrax would be the most likely to occur. In the 2001 terrorist attacks, 11 of the 22 cases were inhalational, resulting in 5 deaths. Before these attacks, the last reported case of inhalational anthrax was in 1976. A single case of inhalational anthrax may represent a bioterrorist threat and a public health emergency.

Extremely rare in normal circumstances, inhalational anthrax reaches a death rate of nearly 40% if treatment is not started in the prodromal phase.

Aerosol inhalation.

Look for nonspecific, flulike symptoms (e.g., low-grade fever, sweats, dry cough, headache, malaise, fatigue, dyspnea, and myalgias) in the first 24 to 48 hours with early chest radiography or computer tomography (CT) demonstrating a widened mediastinum and (often) pleural effusions. Infiltrates may also be present.

Initial symptoms are followed by a sudden onset of high fever and severe respiratory distress along with cyanosis, hypotension, shock, respiratory failure, and sudden death.

See Table 6-5 for drug therapy.

Low risk to personal safety.

Standard precautions.

Low: Inhalational anthrax is not contagious.

Vaccine is available.

Botulism is caused by a group of paralytic neurotoxins produced by the spore-forming, anaerobic, gram-positive bacillus Clostridium botulinum. Intoxication can occur naturally from contaminated foods or rarely as a result of wound or intestinal colonization in humans. There are seven types of botulinum toxins, A through G, although only A, B, E, and F have been implicated in the poisoning of humans. When used as a biological weapon, botulinum toxin is most likely to be dispersed as an aerosol for inhalation, although it could be added to the food or water supply. Botulinum toxins are, by weight, the most toxic agents known, with an LD50^∗ of only 0.001 mcg/kg. Botulinum toxin irreversibly binds to the presynaptic cholinergic neuromuscular junction, blocking acetylcholine release and manifesting as a symmetrical, progressive, descending flaccid paralysis after an 18- to 36-hour incubation period (occasionally up to several days). Multiple cranial nerve palsies are evident early in the course of the disease. Botulinum toxins are odorless and colorless in solution. Five minutes of heating the toxin above 85° C will inactivate the toxin. All materials suspected of containing toxin must be handled with caution. Before the shipment of any botulism-associated specimen, the designated laboratory must be notified and approved by the state health department.

The hallmark symptoms of botulism are difficulty speaking, seeing, and/or swallowing in combination with ptosis on exam. Also look for dilated (enlarged) and/or fixed pupils, diminished gag reflex, tongue weakness, and arm/leg weakness. The mouth may appear dry (xerostomia). The patient is afebrile.

Sensitivity testing: brain scan, spinal fluid examination, nerve conduction test, and Tensilon test for myasthenia gravis (rules out similar diseases, such as Guillain-Barré syndrome).

Low risk to personal safety.

Standard precautions.

Low: Botulism is not contagious.

Equine botulinum antitoxin.

Brucellosis is a systemic infection characterized by an undulant (intermittent) fever pattern. Typically a zoonotic infection of farm animals, the disease is produced in humans by infection with the gram-negative coccobacilli of the genus Brucella. Only four species of Brucella cause infection in humans: B. melitensis (goats and sheep), B. ovis (sheep and goats), B. suis (pigs), B. abortus (cattle), and rarely B. canis (dogs). B. suis and B. melitensis are the most common cause of brucellosis in humans. Weaponization of brucella is likely because of its ease of transmission by aerosol, and it is known to have been weaponized by several countries. During World War II the United States developed brucellosis as a biological weapon and dispersed it via bombs. Aerosolized brucella is highly infectious. In naturally occurring cases, human infection usually is caused by ingestion of contaminated dairy foods or infected animals (e.g., sheep, cattle, goats, or hogs) or through skin wounds.

Aerosol inhalation.

Brucellosis produces both an acute and a debilitating chronic illness. Typical acute systemic symptoms are nonspecific and flulike, and include undulant (intermittent) fevers, headache, chills, profuse sweating, malaise, myalgias, arthralgias, back pain, fatigue, anorexia, and irritability. GI symptoms are common and include nausea, vomiting, diarrhea, ileitis, colitis, and hepatitis. Other findings include bone pain caused by focal infection, pleuritic chest pain, and cough. Adenopathy, pharyngitis, and rash occur more commonly in children. Infection may progress to include the central nervous system (CNS) (meningitis) or the heart (endocarditis). Osteoarticular infections of the spine with paravertebral abscesses are common.

Medium and large joints are also commonly infected. Genitourinary involvement can lead to pyelonephritis, cystitis, and epididymo-orchitis. Infection with Brucella can lead to chronic painful symptoms lasting months. Death rates are less than 2%, and are often associated with endocarditis.

See Table 6-6. Continue therapy for 6 weeks.

Low risk to personal safety.

Standard precautions.

Low: Brucellosis is not contagious.

None available.