Molecular Strain Typing

The microbiology laboratory has made significant contributions to the epidemiology of infectious diseases. The repeated isolation of a specific

TABLE 8.5 Considerations for notifying law enforcement of a possible biologic or chemical terrorism initial investigation at the local level (modified from ref. 17)

Immediate notification of the FBI when:

a. Notification is received from individual or group that a terrorist attack has occurred or will occur.

b. A potential dispersal/delivery device such as munition or sprayer or questionable material is found.

Notification of the FBI as soon as possible after an investigation confirms the following:

a. Illness due to unexplained aerosol, food, or water transmission.

b. At least a single, definitively diagnosed case(s) with one of the following:

—Uncommon agent or disease occurring in a person with no other explanation —Illness due to a genetically altered organism Notification of the FBI after an investigation confirms the following (with no plausible natural explanation):

a. Disease with an unusual geographic, seasonal, or "typical patient" distribution b. Unusual, atypical, or antiquated strain of agent c. Simultaneous clusters of similar illness in noncontiguous areas, domestic or foreign d. Clusters of patients presenting with similar genetic type among agents isolated from temporally or spatially distinct sources microorganism from patients with a given disease or syndrome has helped to prove infectious etiologies. In addition, the isolation and identification of microorganisms from animals, vectors, and environmental sources has been invaluable in identifying reservoirs and verifying modes of transmission. In dealing with an infection, it is often necessary to identify the species of the infecting microorganism in order to prescribe effective therapy. Many of the techniques that have evolved for such purposes are both rapid and accurate but, in general, do not provide the kind of genetic discrimination necessary for addressing epidemiologic questions. The epidemiology of many infectious diseases is becoming more complex. Fortunately, typing methods for bacteria, fungi, protozoa, and viruses have evolved to meet this challenge. Historically, the typing methods that have been used in epidemiologic investigations fall into two broad categories: phenotypic methods and genotypic methods. Phe-notypic methods are those methods that characterize the products of gene expression in order to differentiate strains. For example, the use of biochemical profiles to discriminate between genera and species of bacteria is used as a diagnostic method, but can also be used for biotyping. Other methods, such as phage typing, can be used to discriminate among groups within a bacterial species. Biotyping emerged as a useful tool for epidemiologic investigations in the 1960s and early 1970s, while phage typing of bacteria and serological typing of bacteria and viruses has been used for decades. Today, the majority of these tests are considered inadequate for epidemiologic purposes. First, they

TABLE 8.6 Characteristics of phenotypic typing methods (modified from ref. 23)

Typrng

Strains Typeable

Reproducibility

Discriminatory Power

Ease of Interpretation

Ease of Performance

Biotyping

All

Poor

Poor

Moderate

Easy

Antimicrobial susceptibility patterns

All

Good

Poor

Easy

Easy

Serotyping

Most

Good

Fair

Moderate

Moderate

Bacteriophage

Some

Good

Fair

Difficult

Difficult

or pyocin typing

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