Anthrax, a serious infectious disease caused by the bacterium Bacillus anthracis, necessitates accurate and timely laboratory diagnosis for effective patient management and public health response. Culturing Bacillus anthracis from clinical specimens remains the cornerstone of anthrax diagnosis, considered the gold standard for definitive confirmation. The type of specimen required for bacillus anthracis lab diagnosis is contingent upon the clinical presentation of the disease. Samples suitable for culture include ascites fluid, biopsy tissue, blood, cerebrospinal fluid (CSF), pleural fluid, rectal swabs (in suspected gastrointestinal anthrax cases), and fluid from skin lesions.
In the United States, anthrax is a rare clinical entity for healthcare providers. To aid in the complex process of bacillus anthracis lab diagnosis, the Centers for Disease Control and Prevention (CDC) provides comprehensive clinical guidance and case definitions. These resources are invaluable for clinicians in diagnosing anthrax, meticulously documenting patient histories to ascertain potential exposure routes, and ordering the appropriate diagnostic evaluations. For expert consultation regarding anthrax testing, healthcare professionals are encouraged to contact the CDC’s Emergency Operations Center.
Comprehensive Specimen Collection Guidelines for Bacillus Anthracis Lab Diagnosis
Optimal bacillus anthracis lab diagnosis hinges on the collection of appropriate specimens, ideally before the initiation of antibiotic therapy. The specific types of samples required are determined by the patient’s exposure history and presenting symptoms. The following sections detail the recommended procedures for collecting various specimen types for anthrax testing.
Blood, Plasma, and Serum: Key Specimens for Systemic Anthrax Diagnosis
Blood specimens are particularly crucial in the bacillus anthracis lab diagnosis of inhalation and gastrointestinal anthrax, especially when patients exhibit signs of systemic infection. Real-time polymerase chain reaction (PCR) assay is employed to analyze blood samples, providing rapid confirmation of Bacillus anthracis presence.
For blood collection:
- Collect 10 mL of blood into EDTA or Sodium Citrate tubes (indicated by purple or blue tops, respectively) specifically for anthrax testing.
- In pediatric cases, collect the maximum allowable blood volume based on the child’s size and clinical condition.
- Blood culture and real-time PCR samples should be transported with cold packs to maintain sample integrity.
Plasma is the preferred specimen type for anthrax lethal factor (LF) toxin detection across all forms of anthrax. Specimen collection for LF toxin analysis can occur from the time of suspected exposure or symptom onset up to 18 days post-exposure/onset, with earlier collection being more advantageous.
For plasma collection for LF toxin testing:
- Collect 10 mL of plasma using EDTA purple top tubes.
- Immediately place the specimen on ice for 30 minutes, followed by centrifugation to separate plasma.
- Plasma samples must be shipped on dry ice to ensure preservation of toxin activity.
Serum serves a dual purpose in bacillus anthracis lab diagnosis, enabling both the assessment of the patient’s immune response to anthrax and the detection of anthrax LF toxin. For serological evaluation:
- Two serum samples are required: the first collected within seven days of symptom onset, and the second collected 14-35 days after symptom onset.
- Ideally, the second sample should be obtained two weeks after the first.
- Serum samples for toxin testing can be collected within the same timeframe as plasma samples (zero to 18 days post-exposure/onset), with earlier collection preferred due to potential toxin level reduction during antibiotic treatment.
It is imperative to label serum specimens appropriately to ensure laboratories can process them using Biosafety Level (BSL)-2 practices, as outlined in the CDC’s “Biosafety in Microbiological and Biological Laboratories” guidelines. Whole blood and blood culture bottles should not be submitted for serum testing.
Tissue Biopsies: Essential for Cutaneous and Inhalation Anthrax Diagnosis
Tissue biopsies are critical for the bacillus anthracis lab diagnosis of cutaneous and inhalation anthrax.
For cutaneous anthrax: A full-thickness biopsy of a papule or vesicle, including adjacent skin, is recommended for diagnosing cutaneous anthrax. Ideally, this biopsy should be performed before the patient commences antibiotic treatment.
If the patient is pre-antibiotic treatment or has received antibiotics for less than 24 hours:
- Obtain a full-thickness punch biopsy specimen for both culture and real-time PCR analysis.
- Collect a separate full-thickness punch biopsy sample from the papule or vesicle (including adjacent skin) for histopathology, special stains, and immunohistochemistry (IHC).
If the patient is already receiving antibiotics at the time of presentation:
- Collect a full-thickness punch biopsy sample from the papule or vesicle (including adjacent skin) for histopathology, special stains, and IHC.
- Immerse the sample in 10% buffered formalin for fixation. Freezing is contraindicated.
Analysis of these biopsies may encompass histopathology, special stains, and IHC, providing comprehensive diagnostic information.
For inhalation anthrax: Bronchial or pleural biopsies are necessary for patients presenting with symptoms suggestive of inhalation anthrax.
Formalin-fixed biopsy samples should be shipped to the CDC at room temperature, avoiding freezing. Fresh-frozen biopsy samples require storage at -70°C and shipment on dry ice. Accompanying documentation for biopsy specimens should include:
- A concise clinical history and detailed description of the lesion.
- A chronological account of the lesion’s progression.
- A description of the treatment regimen, including duration and dosage of antibiotics.
- The biopsy date in relation to antibiotic treatment initiation.
- A photograph, digital image, or diagram illustrating the biopsy site(s).
Diagnostic testing on these biopsies may include histopathology, special stains, and IHC. Further guidance on pathology testing is available on the Infectious Diseases Pathology Branch website.
Lesion Swabs: Crucial for Cutaneous and Gastrointestinal Anthrax Diagnosis
Lesion swabs are fundamental for bacillus anthracis lab diagnosis in both cutaneous and gastrointestinal anthrax. For both forms, always collect two distinct swabs: one for real-time PCR and another for culture. The specific swabbing technique varies based on the lesion stage.
For cutaneous anthrax:
- Vesicular stage: Using sterile technique, collect vesicular fluid from intact vesicles with sterile dry swabs.
- Eschar stage: Carefully lift the outer edge of the eschar and insert a sterile moist swab (pre-moistened with sterile saline). Rotate the swab gently for 2-3 seconds beneath the eschar edge before removal to collect eschar material.
- Ulcer stage: If neither vesicle nor eschar is present, swab the ulcer base using a sterile moist swab (pre-moistened with sterile saline).
For gastrointestinal anthrax:
- Oropharyngeal: Employ a swab pre-moistened with sterile saline to aseptically swab the surface and edges of suspected lesions in the oropharynx, buccal cavity, tongue, tonsils, or posterior pharyngeal wall.
- Rectal: Utilize a sterile dry swab to collect a rectal swab.
Samples intended for culture or both culture and real-time PCR should be shipped with cold packs and stored at 2 to 8°C. Samples solely for real-time PCR testing require shipment on dry ice and storage at -70°C.
Pleural and Ascites Fluid Collection: Diagnostic Samples for Inhalation and Gastrointestinal Anthrax
Pleural and ascites fluid collections are valuable specimens in the bacillus anthracis lab diagnosis of inhalation or gastrointestinal anthrax.
- Collect more than 1 mL of pleural fluid into a sterile container for culture, real-time PCR, and anthrax LF toxin testing.
- For optimal test outcomes, pleural fluid specimens should be stored at 2-8°C for no longer than 24 hours.
- Ascites fluid can be obtained from patients exhibiting symptoms of gastrointestinal or inhalation anthrax.
- Collect an appropriate volume of ascites fluid, adhering to local hospital protocols, and ensuring sufficient volume for culture, PCR, and anthrax LF toxin testing.
Specimen Submission Procedures for Bacillus Anthracis Lab Diagnosis
Pre-Shipment Consultation is Mandatory
Prior to shipping any specimens potentially containing B. anthracis, it is crucial to consult with and obtain authorization from your state health department. Furthermore, contact the CDC Emergency Operations Center for an anthrax testing consultation.
The Laboratory Response Network (LRN) plays a vital role in supporting clinical care providers and health departments by offering diagnostic testing services to confirm anthrax, facilitating rapid bacillus anthracis lab diagnosis.
The CDC accepts specimens exclusively from state public health laboratories and federal agencies. Private healthcare providers and institutions must submit specimens to their local state or territorial health department laboratory for initial processing. Contact information for these laboratories can be found on the CDC website.
Guidelines for Shipping Samples
Packaging and shipping specimens that may contain B. anthracis must adhere to stringent guidelines to guarantee safe, intact, and uncontaminated arrival. Detailed instructions are available in the “Anthrax Specimen Packaging and Shipping” document.
Further Reading: Anthrax Specimen Packaging and Shipping
Resources for Bacillus Anthracis Lab Diagnosis
For additional information and resources related to bacillus anthracis lab diagnosis, please refer to the CDC website and relevant publications.
