Microbial forensic data must hold up to the scrutiny of scientists as well as judges and juries. Source: Microsoft Images.
Editor’s Note: This article is comprised of excerpts from a comprehensive, original paper on microbial forensics by Abigail A. Salyers. The paper is also provided on this website as a supplement to this article.
What is microbial forensics?
You have probably heard of commonly used forensic methods such as the analysis of striations on bullets to identify the gun used to commit a crime. But what if a microbe is the weapon of choice, as can occur if a bioterrorist comes to town? Microbes as weapons is not a new topic. There have been reported cases, for example of HIV-infected people intentionally infecting others.
Moreover, microbes can be involved in cases of medical negligence in which a surgeon or nurse causes a patient to contract a post-surgical or other hospital-acquired infection due to inadequate hygiene. There is currently a lawsuit making its way through the Scottish courts against a hospital alleging that inadequate hygiene resulted in the death of a patient.1 It is also conceivable that outbreaks of foodborne disease could spawn lawsuits alleging either negligence or intentional contamination. Tracing the infecting microbe to the company and person(s) of origin will be critical in such cases.
Microbial forensics is the term that is applied to this new type of forensic analysis. Molecular techniques have been used for years to trace outbreaks of microbial diseases, a practice called molecular epidemiology. In fact, there are currently surveillance systems that store and make available DNA fingerprints for microbes that are likely to be involved in hospital-acquired infections and foodborne infections (e.g., PulseNet of the U.S. Centers for Disease Control [CDC], a surveillance system for tracking infections such as Salmonella).2 Although these surveillance systems are still only a few years old, they are rapidly growing in sophistication.
What distinguishes microbial forensics from molecular epidemiology is that microbial forensic data must hold up not only to the scrutiny of scientists in the health care community, but also to the scrutiny of judges and juries. Nonetheless, work done to date on microbial epidemiology will provide an invaluable starting point for the additional work that needs to be done to make microbial forensics ready for its day in court.
The bioterrorism connection
A good example of the problems that need to be solved is provided by the response to the anthrax attack of 2001, in which spores of the bacterium Bacillus anthracis, the cause of anthrax, were disseminated via the mail.3 The effects of this crime extended far beyond the deaths of the 5 people who died of inhalation anthrax.
If a suspect is ever arrested and charged with perpetrating the anthrax attack, spores will be an important part of the physical evidence.
- Prosecutors will have to prove that spores isolated from the suspect’s home or laboratory are in fact THE spores, the ones introduced into the envelopes and mailed.
- The problem with making such a case is that spores of B. anthracis are found widely in soil, especially farm soil in the southern U.S. So the prosecution will have to prove that any spores submitted as evidence were the spores used in the attack and not simply spores that had been tracked into a house or laboratory from a nearby field.
Proving the assertion that the spores introduced as evidence were the ones used to contaminate the envelopes used in the anthrax bioattack may not be as easy as a laboratory scientist, who is familiar with DNA-based molecular epidemiology methods, might think.
- Spores of different strains of B. anthracis and of the vegetative (actively dividing) form of the bacteria, unlike diatoms, look very much alike.
- In fact, different strains of B. anthracis are also very similar to each other at the genome sequence level.
- Given that the error rate for DNA sequencing is not zero, proving that a particular isolate of B. anthracis is the same as the strain used in the bioattack may prove to be difficult.
So, if the assertion to be proven is that the spores found in the home or laboratory of a suspect are the same as those mailed in the envelopes, questions about the meaning of slight variations in test results will have to be answered.
The beginning of a solution — the scientific community responds
The response of the scientific community to the challenge of the hoped-for anthrax court cases provides a good illustration of how scientists proceed in such cases.
- One thing was very clear from the outset — that too little attention had been paid previously to microbial forensics.
- This realization caused scientists to start back at the very beginning, by meeting to identify what information is available, what research remains to be done, and how to proceed as expeditiously as possible.
- Paul Keim, a leader in the early development of DNA-based methods for identifying individual strains of B. anthracis, set the process in action when he approached the American Academy of Microbiology (AAM) about convening a meeting of experts to consider the subject.4
The American Academy of Microbiology is an organization that has a long history of assembling small groups of experts and challenging them to define the future needs for work in a new area of microbiology and was thus the obvious organization to spearhead such an effort. A group of 35 scientists with expertise that might be able to help answer the question of what needs to be done to validate tests that could be put to forensic use was identified by the AAM and met in June 7-9, 2002, in a bucolic setting in Burlington, Vermont. The author of this article was one of the attendees.
For the first time in the history of these AAM-organized meetings, three scientists from the FBI were included. The FBI scientists, all of whom had had direct involvement in investigation of the anthrax case, helped provide the occasional reality check, as other scientists not familiar with work in the field grappled with the question of how to establish standards for evidence collection and for analysis and interpretation of the plethora of new molecular tests, more of which are being published every month. The anthrax attack was not the only example of the possible use of microbial forensics considered by the group of AAM experts. Other examples included intentional contamination of others by HIV-positive individuals and outbreaks of hospital-acquired or foodborne disease. Understandably, however, the anthrax bioattack dominated the discussion.
“Microbial Forensics: A Scientific Assessment,” the report of the conclusions reached by this group of experts, has now been published by the American Academy of Microbiology.5 (See “article references” at the end of this article for information on how to obtain a copy of this report.)
Identification of key challenges and recommendations for finding solutions
Challenge #1: Collecting specimens at the attack site
The first challenge is proper collection of evidence at a site where the release of an infectious microbe is suspected.
Challenge #2: Recognizing that an attack is occurring and diagnosing the disease
In the case of the anthrax bioattack, the agent responsible was identified almost immediately. In other cases of intentional disease transmission, the identity of the microbe being used in the attack may not be apparent so quickly. This is where physicians and other health care workers come in. The physicians are the ones who will recognize, diagnose and treat infected patients.
Challenge #3: Analysis of specimens
The next challenge is the analysis of the specimens collected by first responders and by microbiologists subsequently sent to the site.
Challenge #4: Validation — quality assurance and control
The next challenge is, in some ways, the most formidable one, rigorously validating each analytical method by establishing its limitations, its sensitivity, and its reliability. Also important is the robustness of a method — the assurance that the method can be used successfully in many different laboratories and field conditions, always giving the same results. The credibility of analytical results relies absolutely on proof that the analytical procedure has been thoroughly vetted by experts.
Is all this effort worth the cost?
You do not have to be an expert to realize that the research described in the forgoing material will cost a lot of money. Not only will it be expensive to solve these problems for B. anthracis but also, if full preparedness is the goal, it will be necessary to go through the same process for other agents that might be used in a bioterror attack. What is the taxpayer getting for this large expenditure of money, especially if no further attacks occur?
- One possible benefit is that having a well-prepared response plan in place might deter at least some potential terrorists.
- Perhaps the main benefit, however, is that much of the outcome would also be applicable to tracing natural outbreaks of disease.
- Also, there have been cases in which infected people have intentionally infected others and such cases may well end up in court.
True, specific tests for B. anthracis or Variola (the smallpox virus) would not themselves be of much use, but the development of procedures for reliable collection and storing of microbial specimens and for QA/QC (quality assurance/control) of new molecular tests for identifying and tracking a disease outbreak could be very beneficial in many different infectious disease situations. If, for example, there was a sudden cluster of cases of a disease like Ebola, having a plan for a rapid and effective response could quickly limit the spread of the disease.
Communicating research results
Application of research done on responses to bioattacks to natural disease outbreaks is not a guaranteed benefit, however. Scientists who work in the areas of epidemiology and diagnosis of infectious diseases have always had a tradition of free communication with each other through speeches at open meetings and publication of papers in widely disseminated journals. By contrast, the scientists and politicians who have controlled much of the research on bioterrorism and biodefence have become accustomed to a security system that controls information flow and classifies much of the information obtained.
If those who are responsible for protecting the public against bioattacks insist on keeping most of their discoveries out of the public domain, the public will not be well served. The free communication of scientific findings, free of government censorship, has been proven to be an essential precondition for scientific progress. Also, if an analytical method, for example, is going to be useful in gathering evidence that may be used in court, it must be made available to law enforcement personnel and to lawyers and juries. That is, it will have to become public information.
For these reasons, many scientists are concerned that classifying information about analytical methods will severely limit its use in disease situations that are not bioattacks. There is currently a debate underway about what types of microbiology research results should be published freely. Leading scientific societies such as the American Society for Microbiology and the National Academies of Science have come out in support of free publication of any scientific results that have not been classified, but not all people, especially politicians, agree with this stance.
Editor’s Note: This article is comprised of excerpts from a comprehensive, original paper on microbial forensics by Abigail A. Salyers. The paper is also provided on this Web site as a supplement to this article.
© 2009, American Institute of Biological Sciences. Educators have permission to reprint articles for classroom use; other users, please contact email@example.com for reprint permission. See reprint policy.