Deck 15: Diagnosing Infections

Question 1

C A S E F I L E

A Rash of Symptoms
I was a newly graduated nurse working in the emergency room of a large urban children's hospital when Dale was brought in by his mother. Dale was a 6-year-old who, until a few days prior, had been very healthy. Dale's mother told the triage nurse that Dale was very sick and had a rash "all over." As was policy, Dale was given a mask to wear because he was coughing and was sent back out to the waiting room after having a brief history taken and a set of vital signs.
Dale had been triaged as urgent due to his cough, high fever, and elevated heart rate, so it wasn't long before I called Dale to an exam room to perform a more in-depth history and head-to-toe assessment. According to Dale's mother, Dale had initially complained of a sore throat. Within a day, he also complained of a headache and developed a high fever, which his mother treated appropriately with acetaminophen. He then developed a cough, which his mother assumed was part of a "bad cold." She was not overly concerned until Dale developed a rash, which started on his face and head and rapidly spread to his chest and back, and then to his arms and legs.
I had Dale's mother undress him and put him in an examination gown, and it was only then that I realized the extent of Dale's rash. It was winter and Dale had been covered in clothing from head to toe, having only his jacket removed when seen by the triage nurse. Dressed in a gown, I saw that Dale's mother was not exaggerating-Dale's rash covered almost all of his body. It was a maculopapular rash and did not look like any childhood rash that I had ever seen, before or since.
The physician on duty came in to see Dale and immediately asked Dale to open his mouth. She asked the mother about Dale's immunizations, and his mother admitted that she did not believe in immunizations and Dale had never been immunized. The physician then turned immediately to me and asked me to put Dale in an isolation room. Upon my return, she spoke to Dale's mother, and I will never forget what she said: "Well, it was a very bad decision to not have Dale immunized, because now he has the measles. Not only does your son have the measles, but by bringing him here you exposed everyone in the waiting room to what can be a life-threatening illness." She then ordered a chest X ray and blood work to confirm the diagnosis and said that she would immediately notify the state health department.
• Why was a chest X ray performed?
• Why was the state health department contacted?

Answer 1

A chest X-ray is performed in order to confirm the presence or absence of pneumonia in patients suffering from measles.
According to the law the diseases which should be mandatorily reported to state health authorities are known as reportable or notifiable diseases. Measles is among the reportable diseases and therefore the physician indicated that she would keep the state health department notified. This notification ill help the state health department to take preventive measure from further spread of the disease within the community.

Question 2

Critical thinking is the ability to reason and solve problems using facts and concepts. These questions can be approached from a number of angles and, in most cases, they do not have a single correct answer.
Explain why specimens should be taken aseptically and processed quickly to ensure accurate results, even when nonsterile sites are being sampled and selective media are to be used.

Answer 2

The collection of specimen from the site of infection or investigation plays a crucial role in identification of the infectious agent. The specimen is at the risk of contamination from the normal microbiota inhabiting the person and from the external environment. Collection of specimen from these sites should be executed carefully to identify the infectious agent from normal microbiota. Method of specimen collection depends on the site of infection. For example, blood is drawn through syringe; urine sample is collected through "clean catch method"; sputum is collected with the help of catheter; and the mucus lining of the urethra, vagina or cervix are sampled with an applicator stick or swab.
The specimens should be handled in aseptic condition and processed quickly to ensure that they are not contaminated by the environment or from the person performing the analysis. Contamination will lead to false positive test and will result in administering inappropriate medication which could be fatal.

Question 3

List the three major categories of microbial identification techniques.

Answer 3

The three major categories that exist to test for and identify microbes include phenotypic methods, genotypic methods, and immunologic methods. Phenotypic methods have built in considerations for morphology of the microbe in question. Genotypic methods are increasingly easy and popular and accurate. Immunologic methods include serological analysis.
With phenotypic methods, there are two types of tests that include microscopic and macroscopic morphology. Microbes are observed under the microscope for traits such as shape size, and special structure such as granules, endospores, and capsules. Macroscopically, colonies and other similar traits can be observed to identify the microbe.
With genotypic methods, DNA sequences are isolated and compared against a database of known microbes. It is becoming more fast, easy, and efficient to perform these types of genetic tests, even without the need to culture.
With immunologic methods, microbes have surface antigens that serve as markers for which type of microbe they are. An immune response to antigens is antibodies, so antibodies are used in these tests to identify the type of microbe.

Question 4

Select the correct answer from the answers provided. PCR is used to do which of the following?

A) Amplify the number of copies of genes.
B) Identify the nucleic acid sequence of a gene.
C) Determine the identity of a particular gene.
D) Determine the function of a particular gene.

Question 5

Consequences of improper specimen collection may include
a. having to repeat the test.
b. having to subject the patient to another potentially painful procedure (i.e., bone marrow biopsy, lumbar puncture, blood draw).
c. a delay in appropriate treatment.
d. all of the above.

Question 6

This question connects previous images to a new concept.
From chapter 14, figure 14.10 b. Imagine that this patient is being seen by his or her physician for this unknown rash. What rapid phenotypic test could suggest that this condition is caused by a bacterium? Could a rapid immunoassay or fluorescent procedure be used to identify a specific viral cause? Explain your answer.
Reference: chapter 14, figure 14.10 b

Question 7

Critical thinking is the ability to reason and solve problems using facts and concepts. These questions can be approached from a number of angles and, in most cases, they do not have a single correct answer.
A patient arrives at a health center and the attending nurse suspects an infection. Describe the sequence of general steps he and the health center lab technicians might use to identify the exact identity of the infectious agent.

Question 8

Provide a one-sentence description for each of these three categories.

Question 9

Select the correct answer from the answers provided. Mass spectrometry identifies microbes via

A) fluorescence of antibodies.
B) precipitation reactions.
C) protein fingerprints.
D) fluorescence of antigens.

Question 10

A clinical form used to report data on a patient's specimens may include
a. antibiotic history.
b. patient symptoms.
c. marital status.
d. date and time of specimen collection.
e. a, b, and d.
f. b, c, and d.

Question 11

Critical thinking is the ability to reason and solve problems using facts and concepts. These questions can be approached from a number of angles and, in most cases, they do not have a single correct answer.
Differentiate between the serological tests used to identify isolated cultures of pathogens and those used to diagnose disease from the patient's serum.

Question 12

Identify factors that may affect the identification of an infectious agent from a patient sample.

Question 13

Select the correct answer from the answers provided. Because they are sufficiently unique in their appearances, viruses can sometimes be identified at a family or genus level by which phenotypic method?

A) cell culture
B) PCR
C) electron microscopy
D) ELISA

Question 14

When determining the clinical significance of cultures,
a. the number of microbes is significant.
b. the presence of a single colony of a true pathogen may indicate the presence of the disease if the culture comes from a site known to be sterile (i.e., cerebrospinal fluid).
c. the repeated isolation of a relatively pure culture of any microorganism can mean it is an agent of disease, although this is not always the case.
d. a range of tests may be needed to identify a pathogen.
e. all of the above are true.

Question 15

Critical thinking is the ability to reason and solve problems using facts and concepts. These questions can be approached from a number of angles and, in most cases, they do not have a single correct answer.
a. Seropositivity means having a blood serum that tests positive. Explain why it may or may not develop at the same rate in all patients exposed to the same microbe.
b. Would a high rate of false-positives decrease the sensitivity or specificity of a serological test? (False-positivity was discussed in this chapter, and also in chapter 11.)

Question 16

Compare the types of tests performed on microbial isolates versus those performed on patients themselves.

Question 17

Select the correct answer from the answers provided. Which of the following methods can identify different strains of a microbe?

A) microscopic examination
B) radioimmunoassay
C) serotyping
D) agglutination test

Question 18

Question 19

List at least three different tests that fall in the direct identification category.

Question 20

Select the correct answer from the answers provided. In agglutination reactions, the antigen is a __________ ; in precipitation reactions, it is a __________.

A) soluble molecule; whole cell
B) whole cell; soluble molecule
C) bacterium; virus
D) protein; carbohydrate

Question 21

Explain the main principle behind biochemical testing, and identify an example of such tests.

Question 22

Select the correct answer from the answers provided. Which type of methods is based on a microbe's utilization of nutrients?

A) genotypic
B) immunologic
C) biochemical

Question 23

Explain why PCR is useful for infectious disease diagnosis.

Question 24

Select the correct answer from the answers provided. Which of the following is an in vivo immunologic method?

A) determination of antibody titer
B) tuberculin reaction
C) determination of blood type
D) indirect ELISA

Question 25

List the major steps in a hybridization method of microbial identification.

Question 26

Select the correct answer from the answers provided. Which of the following is the correct pairing of an immunologic test and the subject to be identified?

A) indirect ELISA test/an unknown microbial antigen
B) direct fluorescence antibody test/an unknown antibody
C) Western blot/an unknown microbial antigen or antibody
D) agglutination test/an unknown soluble microbial toxin

Question 27

Explain how rRNA analysis has impacted the process of infectious disease diagnosis.

Question 28

Define the term serology, and explain the immunologic principle behind serological tests.

Question 29

Explain the difference between a direct and an indirect ELISA, providing a clinical application for each.

Question 30

Explain why isolating a pathogen through standard culture methods may become an outdated diagnosis strategy.

Question 31

Name at least three "breakthrough technologies" and the principles behind them.