Laboratory Confirmation of Diseases Resulting From Biological Weapons
Two crucial facts are apparent to those of us who work on preparation for a possible attack by biological weapons: 1) The diseases considered the most likely in this setting are rarely if ever seen in medical practice; and 2) Time to identification and characterization of the agent is vital to marshalling the appropriate resources to defend the population at risk. Defensive measures in the form of antibiotics, vaccines, and various public health measures are useless unless we know how and when to deploy them.
Many laboratory tests are currently available in San Diego County to aid in the diagnosis of some of the more severe biological weaponry. Close communication between the laboratory staff and the clinician is essential if early and accurate diagnosis is to be achieved. All suspected cases of the diseases listed below require immediate reporting by telephone to the community Epidemiology Department of Public Health at (619) 515-6620 or at (858) 565-5255 after hours.
Inhalation Anthrax: Even though the initial site of infection is the lungs, pneumonia is not characteristic and sputum or bronchial washings are not helpful. An enlarged mediastinum on X-ray usually takes days to develop and is often seen only in retrospect. Blood culture is the single best test for identifying cases, but it is important for the laboratory and the clinician to realize that the possibility of anthrax exists because Bacillus spp in blood cultures are usually considered contaminants. If a patient presents with an unexplained severe illness and blood cultures yield large Gram-positive rods in chains of three or more organisms in fewer than 16 hours of incubation, the diagnosis of anthrax should be considered. Typically, the blood culture broth is sub-cultured to plated media after it shows growth, and another overnight incubation is needed to grow the organism for identification. But if anthrax is a possibility, the positive blood culture bottle itself can be sent to the San Diego Public Health Laboratory for direct polymerase chain reaction (PCR) and direct fluorescent antibody (DFA) tests, which are specific for Bacillus anthracis. Results are generally available in just a few hours, and public health laboratory technologists are available around the clock if needed. Testing can also be done on bacterial isolates.
Smallpox (Variola): Smallpox typically has an incubation period of 12–14 days, and patients may be infectious during the two-day prodromal period preceding viremia and formation of skin lesions. The virus prefers the cooler, exposed parts of the body, and lesions typically appear first on the face and hands. Diagnosis during the incubation phase is not possible; lab specimens must be obtained directly from the pox lesions to detect the virus.
To a trained, experienced observer, the lesions may be identifiable, and the Centers for Disease Control and Prevention (CDC) recommends that a digital photo of the lesions be transmitted to their facility in Atlanta, Georgia. Suspect cases should be reported to community epidemiology immediately. Local, state, and federal resources are available to assist in the diagnosis.
It is also recommended that, in an initial case, Varicella zoster virus (VZV) and herpes simplex virus (HSV) be ruled out. For low-risk cases, immunofluorescent stains for VZV and HSV take just a few hours and are done at several local labs such as UCSD and Scripps Clinic. Specimens from higher-risk cases should be sent to the San Diego County Public Health Laboratory. Pending results, the patient should be kept under quarantine in a negative-pressure room, if available, and standard airborne and skin contact precautions instituted. Only persons who have been recently vaccinated should be allowed to care for the patient. If a non-immunized healthcare worker comes into contact with a smallpox patient, the vaccine can still be administered effectively up to four days following exposure. Healthcare givers taking care of the patient should not have a contraindication to receiving vaccinia vaccine.
If smallpox is still being considered, the San Diego Public Health Laboratory can perform a PCR for orthopox viruses, which includes Variola, Vaccinia, and monkeypox viruses, as well as VZV PCR directly on vesicle material. Collect by swab, double wrap in biohazard bags, and have the lab send safely to the public health lab. Testing can be done around the clock and results available within hours.
Brucellosis: While usually not deadly, Brucella is very easy to transmit either by food, water, or aerosol; as few as 10 organisms may cause infection. Symptoms are usually protean, and diagnosis may be difficult. Routine blood culture is the best diagnostic tool, and, since most hospital microbiology labs now use semi-automated blood culture instrumentation, it is not necessary to incubate for extended periods to isolate Brucella. The organism poses a biosafety hazard for lab personnel, so, if brucellosis is suspected, the laboratory should be notified.
The organism is distinctive, and microbiology labs routinely send specimens to the San Diego Public Health Laboratory for PCR confirmatory testing, which takes only a few hours. Serology may also be helpful; a combination of acute and convalescent sera is best.
Botulism: While not a communicable infectious disease, botulism is often discussed in that context with respect to bioterrorism. Symptoms often begin with slurred speech and bilateral cranial neuropathy. Emergency room physicians should be especially suspicious if more than one case presents in a short time frame. Laboratory confirmation is laborious and time consuming. The inoculation of mice with patients’ serum or an emulsion of the suspected food is still the test of choice. Antitoxin can only be released after consultation with Community Epidemiology and the California State Department of Health. Any physician ordering the test must personally contact both of these agencies to discuss the possibility of botulism. Community Epidemiology can facilitate the process. Specimens are best sent directly to the San Diego Public Health Laboratory, which will then forward them to the State Microbial Diseases Laboratory.
Pneumonic Plague (Black Death): Yersinia pestis can be spread by aerosol to produce a fulminating form of pneumonia that is potentially transmissible. Routine sputum and blood cultures are usually best for isolating the bacteria, and the San Diego Public Health Laboratory can perform PCR and DFA on the isolated organism. Organisms can be seen on Gram stain directly on clinical material as small bipolar staining Gram-negative rods, but if not suspected may not be immediately considered by the lab.
Tularemia: Like Brucella, Francisella tularensis is not usually deadly but can be transmitted easily with just a few organisms. Aerosol release would usually result in pleuropneumonitis, but eye and ulceroglandular disease might also be seen. Routine blood and sputum cultures are the preferred tests, but the organism is slow growing and may be missed on initial examination of cultures. The San Diego Public Health Laboratory is equipped to make an immediate confirmation by PCR and direct FA once the organism is suspected.
Summary
Unfortunately, it is not possible to predict each and every bioterrorism scenario and every organism possible for use as a biological weapon. Any healthcare professional at any time might be the one to have the first encounter with a bioterrorism victim post attack. At that moment we all become public health workers, using every tool we have to defend the population. Stay alert.