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2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings

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Table 3. Infection Control Considerations For High-Priority (Cdc Category A) Diseases That May Result From Bioterrorist Attacks Or Are Considered To Be Bioterrorist Threats

Disease Anthrax
Site(s) of Infection; Transmission Mode
Cutaneous and inhalation disease have occurred in past bioterrorist incidents
Cutaneous (contact with spores);RT (inhalation of spores);GIT (ingestion of spores - rare)
Comment: Spores can be inhaled into the lower respiratory tract. The infectious dose of B. anthracis in humans by any route is not precisely known. In primates, the LD50 (i.e., the dose required to kill 50% of animals) for an aerosol challenge with B. anthracis is estimated to be 8,000–50,000 spores; the infectious dose may be as low as 1-3 spores
Incubation Period Cutaneous: 1 to12 days; RT: Usually 1 to 7 days but up to 43 days reported; GIT: 15-72 hours
Clinical Features Cutaneous: Painless, reddish papule, which develops a central vesicle or bulla in 1-2 days; over next 3-7 days lesion becomes pustular, and then necrotic, with black eschar; extensive surrounding edema.
RT: initial flu-like illness for 1-3 days with headache, fever, malaise, cough; by day 4 severe dyspnea and shock, and is usually fatal (85%-90% if untreated; meningitis in 50% of RT cases.
GIT: ; if intestinal form, necrotic, ulcerated edematous lesions develop in intestines with fever, nausea and vomiting, progression to hematemesis and bloody diarrhea; 25-60% fatal
Diagnosis Cutaneous: Swabs of lesion (under eschar) for IHC, PCR and culture; punch biopsy for IHC, PCR and culture; vesicular fluid aspirate for Gram stain and culture; blood culture if systemic symptoms; acute and convalescent sera for ELISA serology
RT: CXR or CT demonstrating wide mediastinal widening and/or pleural effusion, hilar abnormalities; blood for culture and PCR; pleural effusion for culture, PCR and IHC; CSF if meningeal signs present for IHC, PCR and culture; acute and convalescent sera for ELISA serology; pleural and/or bronchial biopsies IHC.
GIT: blood and ascites fluid, stool samples, rectal swabs, and swabs of oropharyngeal lesions if present for culture, PCR and IHC
Infectivity Cutaneous: Person-to-person transmission from contact with lesion of untreated patient possible, but extremely rare.
RT and GIT: Person-to-person transmission does not occur.
Aerosolized powder, environmental exposures: Highly infectious if aerosolized
Recommended Precautions Cutaneous: Standard Precautions; Contact Precautions if uncontained copious drainage.
RT and GIT: Standard Precautions.
Aerosolized powder, environmental exposures: Respirator (N95 mask or PAPRs), protective clothing; decontamination of persons with powder on them (http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5135a3.htm)
Hand hygiene: Handwashing for 30-60 seconds with soap and water or 2% chlorhexidene gluconate after spore contact (alcohol handrubs inactive against spores [Weber DJ JAMA 2003; 289:1274]).
Post-exposure prophylaxis following environmental exposure: 60 days of antimicrobials (either doxycycline, ciprofloxacin, or levofloxacin) and post-exposure vaccine under IND
Disease Botulism
Site(s) of Infection; Transmission Mode GIT: Ingestion of toxin-containing food, RT: Inhalation of toxin containing aerosol cause disease.
Comment: Toxin ingested or potentially delivered by aerosol in bioterrorist incidents. LD50 for type A is 0.001 μg/ml/kg.
Incubation Period 1-5 days.
Clinical Features Ptosis, generalized weakness, dizziness, dry mouth and throat, blurred vision, diplopia, dysarthria, dysphonia, and dysphagia followed by symmetrical descending paralysis and respiratory failure.
Diagnosis Clinical diagnosis; identification of toxin in stool, serology unless toxin-containing material available for toxin neutralization bioassays.
Infectivity Not transmitted from person to person. Exposure to toxin necessary for disease.
Recommended Precautions Standard Precautions.
Disease Ebola Hemorrhagic Fever
Site(s) of Infection; Transmission Mode As a rule infection develops after exposure of mucous membranes or RT, or through broken skin or percutaneous injury.
Incubation Period 2-19 days, usually 5-10 days
Clinical Features Febrile illnesses with malaise, myalgias, headache, vomiting and diarrhea that are rapidly complicated by hypotension, shock, and hemorrhagic features. Massive hemorrhage in < 50% pts.
Diagnosis Etiologic diagnosis can be made using RT-PCR, serologic detection of antibody and antigen, pathologic assessment with immunohistochemistry and viral culture with EM confirmation of morphology.
Infectivity Person-to-person transmission primarily occurs through unprotected contact with blood and body fluids; percutaneous injuries (e.g., needlestick) associated with a high rate of transmission; transmission in healthcare settings has been reported but is prevented by use of barrier precautions.
Recommended Precautions Hemorrhagic fever specific barrier precautions: If disease is believed to be related to intentional release of a bioweapon, epidemiology of transmission is unpredictable pending observation of disease transmission. Until the nature of the pathogen is understood and its transmission pattern confirmed, Standard, Contact and Airborne Precautions should be used. Once the pathogen is characterized, if the epidemiology of transmission is consistent with natural disease, Droplet Precautions can be substituted for Airborne Precautions. Emphasize: 1) use of sharps safety devices and safe work practices, 2) hand hygiene; 3) barrier protection against blood and body fluids upon entry into room (single gloves and fluid-resistant or impermeable gown, face/eye protection with masks, goggles or face shields); and 4) appropriate waste handling. Use N95 or higher respirators when performing aerosol-generating procedures. In settings where AIIRs are unavailable or the large numbers of patients cannot be accommodated by existing AIIRs, observe Droplet Precautions (plus Standard Precautions and Contact Precautions) and segregate patients from those not suspected of VHF infection. Limit blooddraws to those essential to care. See text for discussion and Appendix A for recommendations for naturally occurring VHFs.
Disease Plague2
Site(s) of Infection; Transmission Mode RT: Inhalation of respiratory droplets.
Comment: Pneumonic plague most likely to occur if used as a biological weapon, but some cases of bubonic and primary septicemia may also occur. Infective dose 100 to 500 bacteria
Incubation Period 1 to 6, usually 2 to 3 days.
Clinical Features Pneumonic: fever, chills, headache, cough, dyspnea, rapid progression of weakness, and in a later stage hemoptysis, circulatory collapse, and bleeding diathesis
Diagnosis Presumptive diagnosis from Gram stain or Wayson stain of sputum, blood, or lymph node aspirate; definitive diagnosis from cultures of same material, or paired acute/convalescent serology.
Infectivity Person-to-person transmission occurs via respiratory droplets risk of transmission is low during first 20-24 hours of illness and requires close contact. Respiratory secretions probably are not infectious within a few hours after initiation of appropriate therapy.
Recommended Precautions Standard Precautions, Droplet Precautions until patients have received 48 hours of appropriate therapy. Chemoprophylaxis: Consider antibiotic prophylaxis for HCWs with close contact exposure.
Disease Smallpox
Site(s) of Infection; Transmission Mode RT Inhalation of droplet or, rarely, aerosols; and skin lesions (contact with virus).
Comment: If used as a biological weapon, natural disease, which has not occurred since 1977, will likely result.
Incubation Period 7 to 19 days (mean 12 days)
Clinical Features Fever, malaise, backache, headache, and often vomiting for 2-3 days; then generalized papular or maculopapular rash (more on face and extremities), which becomes vesicular (on day 4 or 5) and then pustular; lesions all in same stage.
Diagnosis Electron microscopy of vesicular fluid or culture of vesicular fluid by WHO approved laboratory (CDC); detection by PCR available only in select LRN labs, CDC and USAMRID
Infectivity Secondary attack rates up to 50% in unvaccinated persons; infected persons may transmit disease from time rash appears until all lesions have crusted over (about 3 weeks); greatest infectivity during first 10 days of rash.
Recommended Precautions Combined use of Standard, Contact, and Airborne Precautionsb until all scabs have separated (3-4 weeks).
Only immune HCWs to care for pts; post-exposure vaccine within 4 days.
Vaccinia: HCWs cover vaccination site with gauze and semi-permeable dressing until scab separates (>21 days). Observe hand hygiene.
Adverse events with virus-containing lesions: Standard plus Contact Precautions until all lesions crusted
Disease Tularemia
Site(s) of Infection; Transmission Mode RT: Inhalation of aerosolized bacteria. GIT: Ingestion of food or drink contaminated with aerosolized bacteria.
Comment: Pneumonic or typhoidal disease likely to occur after bioterrorist event using aerosol delivery. Infective dose 10-50 bacteria
Incubation Period 2 to 10 days, usually 3 to 5 days
Clinical Features Pneumonic: malaise, cough, sputum production, dyspnea;
Typhoidal: fever, prostration, weight loss and frequently an associated pneumonia.
Diagnosis Diagnosis usually made with serology on acute and convalescent serum specimens; bacterium can be detected by PCR (LRN) or isolated from blood and other body fluids on cysteine-enriched media or mouse inoculation.
Infectivity Person-to-person spread is rare.
Laboratory workers who encounter/handle cultures of this organism are at high risk for disease if exposed.
Recommended Precautions Standard Precautions

(www.bt.cdc.gov) a

a Abbreviations used in this table: RT = respiratory tract; GIT = gastrointestinal tract; CXR = chest x-ray; CT = computerized axial tomography; CSF = cerebrospinal fluid; and LD50 – lethal dose for 50% of experimental animals; HCWs = healthcare worker; BSL = biosafety level; PAPR = powered air purifying respirator; PCR = polymerase chain reaction; IHC = immunohistochemistry

bTransmission by the airborne route is a rare event; Airborne Precautions is recommended when possible, but in the event of mass exposures, barrier precautions and containment within a designated area are most important 204, 212.

c Vaccinia adverse events with lesions containing infectious virus include inadvertent autoinoculation, ocular lesions (blepharitis, conjunctivitis), generalized vaccinia, progressive vaccinia, eczema vaccinatum; bacterial superinfection also requires addition of contact precautions if exudates cannot be contained 216, 217.

2 Pneumonic plague is not as contagious as is often thought. Historical accounts and contemporary evidence indicate that persons with plague usually only transmit the infection when the disease is in the end stage. These persons cough copious amounts of bloody sputum that contains many plague bacteria. Patients in the early stage of primary pneumonic plague (approximately the first 20–24 h) apparently pose little risk [1, 2]. Antibiotic medication rapidly clears the sputum of plague bacilli, so that a patient generally is not infective within hours after initiation of effective antibiotic treatment [3]. This means that in modern times many patients will never reach a stage where they pose a significant risk to others. Even in the end stage of disease, transmission only occurs after close contact. Simple protective measures, such as wearing masks, good hygiene, and avoiding close contact, have been effective to interrupt transmission during many pneumonic plague outbreaks [2]. In the United States, the last known cases of person to person transmission of pneumonic plague occurred in 1925 [2].

1. Wu L-T. A treatise on pneumonic plague. Geneva: League of Nations, 1926. III. Health.

2. Kool JL. Risk of person to person transmission of pneumonic plague. Clinical Infectious Diseases, 2005; 40 (8): 1166-1172

3. Butler TC. Plague and other Yersinia infections. In: Greenough WB, ed. Current topics in infectious disease. New York: Plenum Medical Book Company, 1983.

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