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Answers to Clinical Case
Studies
CHAPTER 1 A Brief History of Microbiology
Clinical Case Study: Remedy for Fever or Prescription for Death? (p. 20)
1. It is quite possible that a lot of the dark-skinned refugees had developed or acquired
immunity from prior exposure to and survival of yellow fever, as it was a problem (endemic)
in their homeland. At first, it might have appeared as if the Caucasian population in
Philadelphia was primarily affected by yellow fever.
2. Unknown to the people of that era, mosquitoes rarely migrate farther than one mile from their
original birthplace. Many of the affluent (wealthy Philadelphians) who left the city for their
countryside estates simply did not experience the epidemic. They had little or no direct
exposure to infected mosquitoes. Yellow fever is not passed from one human to another
(contagious).
3. Early American settlers believed that the cold weather somehow purified the air and that
exposing themselves and even furniture to the frost was purifying. In a way this principle was
correct in that the frost may have killed the live infected mosquitoes. However, as the
dormant infected larva began to hatch the following year, the epidemic reoccurred in other
nearby areas.
CHAPTER 2 The Chemistry of Microbiology
Clinical Case Study: Raw Oysters and Antacids: A Deadly Mix? (p. 39)
1. Antacids raise the pH of the stomach, allowing more cells of Vibrio to survive and cause
disease.
2. Antacids raise the pH.
3. Oyster lovers should acquire their treats from untainted waters, cook the oysters thoroughly,
or decline to assuage their oyster cravings.
CHAPTER 6 Microbial Nutrition and Growth
Clinical Case Study: Daniel’s Dilemma (p. 175)
1. Biofilms of dental plaque have led to the complete destruction of Daniel’s teeth. Lesions in
his mouth allowed bacteria to invade his blood and affect his heart. All of his signs and
symptoms relate to the underlying dental disease: unsociability and truancy due to poor selfimage resulting from lack of healthy teeth; inability to properly enunciate due to lack of teeth;
and malnutrition and crying due to painfulness of chewing, resulting in eating too little.
Bacterial blood infection resulted in heart and circulation problems. (Once the dental caries
were dealt with, Daniel became a voracious eater and a normally sociable child.)
2. Daniel needs to brush his teeth regularly to remove plaque buildup. His parents can ensure
that he eats properly and brushes his teeth. Dental professionals must remove the diseased
teeth, provide dentures until the permanent teeth can grow in, and treat the bacterial infection
with antibiotics.
3. His parents should remove sucrose from his diet to inhibit the formation of Streptococcus
mutans colonization and biofilm formation.
4. Biofilms are synergistic communities of microorganisms. By physically disrupting their
relationships with one another, brushing inhibits the formation of stable biofilms.
CHAPTER 10 Controlling Microbial Growth in the Body:
Antimicrobial Drugs
Clinical Case Study: Antibiotic Overkill (p. 287)
1. The powerful antibiotic had killed the bacterial microbiota present in the oral mucosa and
vagina. This allowed yeast to flourish, resulting in her symptoms.
2. The yeast no longer had to compete for nutrients in the absence of the natural bacteria.
Microbial antagonism was drastically reduced.
3. She needs to be aware of opportunistic yeast infections when taking oral antibiotics and selfmedicate with over-the-counter antifungal agents.
Clinical Case Study: To Treat or Not to Treat? (p. 303)
1. Spectrum of action, efficacy (strain sensitivity to the drug), routes of administration (ability to
maintain an IV access), safety and side effects (toxicity, allergies, tolerance for treatment),
client age and physical condition, resources to continue extensive treatment.
2. Because the risks of TB in the brain are more severe than the risks of multi-drug treatment,
the doctors decided to treat the child for MDR-TB. A six-week culture from the infant’s
bronchial secretions produced the MDR strain of TB; therefore, the more aggressive
treatment continued well over 18 months before the infection was finally cleared.
CHAPTER 13 Characterizing and Classifying Viruses, Viroids,
and Prions
Clinical Case Study: Invasion from Within or Without? (p. 404)
1. The man has a prion-induced disease. There was no mention of a family history of
Creutzfeldt-Jacob disease, which tends to occur in older people who have methionine as the
129th amino acid in PrP protein. It is unlikely he was invaded by prions from within; rather, it
is likely he acquired the prion from without.
It is true that the young man was an avid hunter in the Colorado area, and chronic wasting
disease (similar to BSE) is prevalent in elk populations; nevertheless, no cases of human
infection have been reported from the consumption of game animals. However, consumption
of meat in Europe during the time bovine spongiform encephalopathy (BSE) was a public
health concern is a risk factor for variant Creutzfeldt-Jacob disease. This is the likely source
of his infection.
2. It was determined that her husband had variant Creutzfeldt-Jakob disease; therefore, the
family is not at risk.
CHAPTER 14 Infection, Infectious Diseases, and Epidemiology
Clinical Case Study: A Deadly Carrier (p. 413)
1. When a large number of cases of a fecal-orally transmitted disease occur in a community in a
short period of time, the public water supply is among the first things investigated.
2. Public health officials could notify the community to boil all water before drinking it or using
it to prepare foods, wash dishes, brush teeth, etc. A privy could be placed at the job site and
the workers educated about the necessity of using it. The first Sulfa drug, which is not an
antibiotic, was just coming on the market and may have been used to treat the carrier and
victims.
Clinical Case Study: TB in the Nursery (p. 425)
1. Most often doctors’ staffs are busy and may overlook the obvious. Upper respiratory
disturbances that coincide with fever should stimulate caregivers to “THINK TB.” This was
the national slogan for tuberculosis awareness several years ago. Simply keeping this possible
diagnosis in mind would remind the caregiver to assess for this reemerging disease.
2. At a minimum, feverous staff members should be restricted from working with patients.
3. Education is a powerful tool. Posters and other visuals could be used in waiting rooms.
Caregivers can insist that patients with respiratory problems wear masks while waiting.
Clinical Case Study: Unusual Transmission of West Nile Virus (p. 426)
1. Anyone bitten by an infected mosquito, especially if elderly or immunocompromised, is at
risk.
2. How was the donor infected? Who else was infected by the donors?
3. Blood and other human tissues should be checked for the presence of West Nile virus and its
antigens before transplant.
Clinical Case Study: Legionella in the Produce Aisle (p. 434)
1. This is a local epidemic.
2. This is an analytical epidemiological study based upon a descriptive study.
3. Legionella is transmitted in water droplets; therefore, patients should be questioned about
locations where they may have breathed Legionella.
4. Legionella lives in water. Epidemiologists should check the air-conditioning systems, misters,
and any other device that can aerosolize water droplets.
5. The victims breathed water droplets contaminated with Legionella when the vegetable
misters were on. Many store patrons shopped when the misters were off. Furthermore,
Legionella primarily causes disease in elderly immunocompromised individuals. The store
owners should regularly clean and sterilize the vegetable misters and storage tanks.
CHAPTER 15 Innate Immunity
Clinical Case Study: Evaluating an Abnormal CBC (p. 451)
1. Remember that bleeding cleanses a wound of potentially infectious microbes and normal
coagulation prevents the entry of microorganisms. A very low platelet count could result in
excessive bleeding and failure of coagulation. Routine health care should avoid situations that
might result in excessive bleeding, such as shaving accidents, vigorous tooth brushing, or
unnecessary needlesticks.
2. This patient is at risk for a fatal infection. He must be protected from anything that interrupts
skin integrity, which would place him at risk for an infection that he does not have enough
white blood cells to fight. For example, this patient should not receive intramuscular
injections, rectal temperature thermometers, or enemas. Additional precautions include
isolation, restriction of visitors, aand avoidance of plants, fresh fruits, and vegetables.
CHAPTER 18 AIDS and Other Immune Disorders
Clinical Case Study: The First Time’s Not the Problem (p. 527)
1.
2.
3.
4.
Type I hypersensitivity, also known as allergy.
Antihistamine.
Local inflammation.
There is a risk of life-threatening anaphylaxis, which is a more dramatic type 1
hypersensitivity reaction in which subsequent exposure to an allergen triggers rapid
degranulation of basophils, mast cells, and eosinophils, releasing inflammatory chemicals.
5. “Skin testing,” in which a small pinprick with the suspected allergen subsequently
demonstrates redness, swelling, and itching if sensitivity is present, can indicate the level of
future risk.
6. Severe allergic reaction can commence rapidly after a sting occurs, and the whole body is
involved. The boy would likely feel dizzy, nauseated, and weak. There may be stomach
cramps and diarrhea, itching around the eyes, coughing, hives, and vomiting. He may
experience difficulty in breathing, suffer a drop in blood pressure, and develop shock and
unconsciousness.
7. The boy should avoid bees, wear clothing to cover skin, and use insect repellent. The child’s
school should be made aware of his bee allergy with written notification of the condition,
consent for treatment, and access to antihistamines and epinephrine, and his friends should
also be informed. Steven should wear a Medic-Alert bracelet. The family needs to fill a
prescription for epinephrine immediately, have training on its use, and always have it handy.
Steven may be able to become desensitized through therapy with an allergy specialist.
Clinical Case Study: A Case of AIDS (p. 546)
1. Confirmatory tests demonstrate antibodies against HIV in the blood, though this does not
absolutely verify the presence of HIV in the body; such tests only indicate exposure to HIV.
2. Given his history of drug usage, he likely contracted the virus through sharing contaminated
needles. He may have been infected sexually.
3. As HIV destroyed the patient’s helper T cell population, he became incapable of mounting an
adaptive immune response to opportunistic pathogens such as Candida and Pneumocystis.
4. The patient’s blood is contaminated with HIV and poses a threat to health care and laboratory
workers who might contact the blood with broken skin or mucous membranes. The blood
should be properly labeled, sealed in containers for transport, and sterilized as soon as it is no
longer needed.
CHAPTER 19 Microbial Diseases of the Skin and Wounds
Clinical Case Study: A Painful Rash (p. 565)
1. Immediate treatment is critically important to survival. Although several kinds of bacteria can
cause the same symptoms, treatment is essentially the same regardless of agent.
2. Necrotizing fasciitis. Treatment includes a combination of broad-spectrum antibiotics
administered IV, and surgical removal of the infected tissue.
3. Impetigo is a superficial skin infection that causes shallow red patches that are not firm, and it
is not accompanied by fever.
4. Streptococcus pyogenes is the leading cause of necrotizing fasciitis, although several other
bacteria can, on rare occasions, be the infecting agent.
5. A small break in the skin could have allowed the bacteria access to the deeper tissues.
6. Hyaluronidase and streptokinase allow the bacteria to readily invade and damage tissue, and
spread throughout the body, while exotoxin A causes the fever and chills.
7. Necrotizing fasciitis is highly invasive, moving from the initial site of infection to
surrounding tissues in a matter of hours, and the toxins and the bacteria themselves can very
rapidly become systemic.
Clinical Case Study: A Sick Soldier (p. 585)
1. Yes. The soldier has cutaneous leishmaniasis.
2. Superficial infections are generally not treated. If treatment is called for, the heavy metal
antimony is administered in the form of sodium stibogluconate. The treatment is toxic to the
patient and should be monitored closely.
3. The bite of a sand fly vector is the source of cutaneous infection.
4. Reducing rodent and stray dog populations around human habitations, wearing clothing that
covers the skin and using insect repellent can reduce sand fly bites.
5. The protozoan infects macrophages and is able to prevent killing by the macrophage. The
infected macrophages recruit other macrophages to the infection site, providing additional
cells for the parasite to infect.
Clinical Case Study: The Scratching Teacher (p. 586)
1. The teacher made direct contact with the infected boy.
2. Because the hypersensitivity reaction is primarily to the mite eggs and feces, it can persist
even after the mites are killed.
3. No. Only if the itching persists beyond four weeks should she consider retreatment.
4. Because infection can be transmitted by body contact or via shared clothing or towels, all her
family members should be treated. Schools generally have policies regarding notification of
families when there is a contagious infection.
CHAPTER 20 Microbial Diseases of the Nervous System and
Eyes
Clinical Case Study: The Frowning Actor (p. 602)
1. One of seven antigenically distinct botulism neurotoxins. It is approved for cosmetic use.
2. Botulism toxin binds to presynaptic neuron cytoplasmic membranes, blocking the release of
acetylcholine and thereby preventing contraction of the postsynaptic muscle.
3. As sprouting of new neuron terminals occurs, a functional synapse is reestablished and the
clinical effect of Botox subsides. The muscle recovers its ability to contract. Recovery
generally takes three to six months.
4. No, the injection contains botulism toxin, not Clostridium botulinum.
5. The toxin diffused into areas adjacent to the injection site and relaxed unintended muscles.
Clinical Case Study: The Man with No Feelings (p. 608)
1. Physicians positively diagnose leprosy by demonstration of a positive skin reaction to leprosy
antigen or through direct observation of acid-fast rods in tissue samples.
2. Tuberculoid leprosy is characterized by loss of feeling in the extremities.
3. Therapy consists of multiple drugs such as clofazimine, rifampin, and dapsone for two years.
4. Leprosy is not very contagious. Health care personnel are not at risk.
Clinical Case Study: A Threat from the Wild (p. 614)
1.
2.
3.
4.
Rabies.
Rabies virus.
Negri bodies, which are intracellular aggregates of rabies viruses.
Because there was no obvious wound, thorough cleansing and local application of human
rabies immune globulin (HRIG) would not have been possible; however, injection of HRIG
and immediate vaccination with rabies vaccine might have saved him.
Clinical Case Study: A Very Sick Sophomore (p. 619)
1. Meningitis.
2. Several bacteria, and some viruses, cause meningitis. The severity of the symptoms suggests
bacterial meningitis.
3. Leukocytes are also present in the CSF.
4. The diagnosis is meningococcal meningitis, caused by Neisseria meningitidis.
5. Meningococcal meningitis is highly contagious in close living quarters. Other students in the
dorm may have been exposed.
6. Vaccination.
CHAPTER 21 Microbial Cardiovascular and Systemic Diseases
Clinical Case Study: A Heart-Rending Experience (p. 631)
1. The construction worker may have been using intravenous drugs in the bathroom—a location
replete with Escherichia coli. Addicts often lick their needles prior to injection, which could
lead to pathogens being directly injected into the bloodstream.
2. E. coli produced vegetations on the valves of the heart, rendering them unable to close
correctly. The body’s immune response attacked the invader, causing further tissue
destruction and scarring. The incompetent cardiovascular system led to shortness of breath.
3. The construction worker worsened rapidly when ER personnel added fluid to his already
insulted cardiovascular system. A ventilator was required to provide respiratory support to the
man’s fluid-filled lungs. The steroid actually decreased his immune system’s natural ability to
fight E. coli, allowing the invader to rapidly multiply and increase the intensity of the client’s
symptoms.
Clinical Case Study: A Sick Camper (p. 638)
1. The woman was probably bitten by an infected flea.
2. Except for the bubo (swelling in the groin), the signs and symptoms are common to a variety
of bacterial infections. Prompt diagnosis and treatment are crucial because the disease
progresses rapidly and is deadly in the absence of treatment.
3. The history of a recent visit to the southwestern United States and the presence of the bubo
mean that plague caused by Yersinia pestis is the most likely diagnosis.
4. Prompt treatment with antibacterials such as streptomycin, tetracycline, etc.
5. Once plague is confirmed, public health officials, animal control officers, and wildlife
managers in the area where she camped and hiked should be notified to be alert for additional
human cases and for sick animals.
Clinical Case Study: A Tired Freshman (p. 646)
1. The doctor should suspect infectious mononucleosis (“mono”), caused by Epstein-Barr virus.
2. The student most likely contracted the infection by kissing his girlfriend.
3. He may develop swollen lymph nodes, an enlarged spleen, or nausea, or some combination
thereof.
4. EBV infects B lymphocytes, triggering a cytotoxic immune response that targets the infected
B lymphocytes, which in turn accounts for many of the symptoms of mono.
5. Treatment to relieve symptoms is the standard of care for infectious mononucleosis.
Clinical Case Study: An Opportunistic Infection (p. 653)
1.
2.
3.
4.
5.
Serologic tests to detect pathogen antigens, or PCR.
Toxoplasmosis.
One hundred CD4 T lymphocytes per ml of blood.
The man likely ate undercooked meat.
People with functional immune systems contain the infection and are asymptomatic or have
few, mild symptoms.
CHAPTER 22 Microbial Diseases of the Respiratory System
Clinical Case Study: The Coughing Sister (p. 681)
1. An increasing number of cases of pertussis have been reported to the CDC since the 1980s.
The increases are greatest among adolescents (aged 10–19 years), but an increase is also seen
among infants younger than 5 months old.
2. A. Catarrhal, lasting one to two weeks, characterized by coryza, mild fever, and a
nonproductive cough.
B. Paroxysmal, lasting two to six weeks, characterized by paroxysmal cough, inspiratory
“whoop,” and posttussive vomiting.
C. Convalescent, which may last two weeks or more. The paroxysms gradually decrease in
frequency and intensity.
3. It is not always present, and adults rarely have the classic “whoop.”
4. A single dose of DTaP in place of the Td booster previously recommended.
5. Infants under the age of 12 months have more serious illness and are more likely to have
complications and require hospitalization. In recent years, 15 to 21 infant deaths from
pertussis have been reported to CDC annually. The vaccine is recommended for all infants at
two, four, and six months of age, with an additional dose at 15–18 months and at four to six
years of age. At least three doses are needed to have maximum benefit, but even one or two
doses will provide some protection. Because the six-week-old has not had any DTaP, she is at
the highest risk. The medical record for the five-year-old confirms she has had five doses of
DTaP.
6. Nasopharyngeal culture is the preferred diagnostic test, but Bordetella pertussis is difficult to
grow. Polymerase chain reaction (PCR) can be used in conjunction with culture when cough
has been present for less than three weeks or any symptoms have been present for four weeks.
7. Treatment is unlikely to be beneficial if symptoms are present for longer than one week.
However, treatment may reduce the chance of disease transmission. Treatment during the
first four weeks may provide benefit and is therefore recommended with erythromycin.
8. It spreads easily from person to person in respiratory droplets, and is most contagious before
the coughing starts. Vaccination is the most effective way to prevent spread, but the sixweek-old should be evaluated for treatment with antibiotics if Marjorie’s culture and PCR
indicate pertussis. Symptomatic individuals should cover their mouth when coughing, wash
their hands frequently, and avoid exposure to others at risk (unvaccinated).
Clinical Case Study: Influenza (p. 683)
1. Influenza vaccines are nonliving subunit vaccines (see Chapter 17) and therefore cannot
cause infection.
2. The man’s visit to a market in Hong Kong exposed him to animal reservoirs of influenza A.
3. The flu vaccine provides protection from the three or four antigenic strains most commonly
circulating in the human population, not all possible strains, and not strains from animal
reservoirs.
4. New genetic and antigenic strains of influenza A develop constantly due to HA and NA gene
recombination in coinfected hosts, and constant genetic mutation (“genetic drift”).
5. No. Prescription drugs for influenza are effective only if taken within 36–48 hours of
exposure. By his account, the man was exposed more than 48 hours prior to visiting his
physician.
Clinical Case Study: A Blue Baby (p. 686)
1. The presumptive diagnosis is respiratory syncytial virus (RSV) infection.
2. RSV infection is diagnosed using immunofluorescent antibody or ELISA assays of
respiratory fluid to detect viral antigens.
3. The child needs oxygen administered immediately, and antibiotics. If the child does not
improve, treatment with anti-RSV immunoglobulin or ribaviron aerosol may be needed.
4. No, there is no vaccine for RSV.
5. Yes. Older children typically develop mild symptoms, due to a better developed immune
system and larger airways.
CHAPTER 23 Microbial Diseases of the Digestive System
Clinical Case Study: The Case of the Lactovegetarians (p. 719)
1. The pathogen is most likely Campylobacter jejuni.
2. It is likely that the whole unpasteurized milk was contaminated with bird feces containing
Campylobacter.
3. Campylobacter is not a contagious organism; colleagues are not at risk.
4. Campylobacter reservoirs include poultry, rabbits, pigs, and cattle. Since the patients are
lactovegetarians, it is unlikely they were infected by eating contaminated meat.
Clinical Case Study: Painful Dysentery (p. 723)
1. The diagnosis is amebic dysentery, caused by the protozoan Entamoeba histolytica.
2. E. histolytica also causes luminal amebiasis and invasive extraintestinal amebiasis.
3. Luminal amebiasis is an asymptomatic to very mild intestinal infection. Invasive
extraintestinal amebiasis is a severe, potentially fatal, disease in which the protozoan spreads
into various organs of the body, including the liver, spleen, and brain, causing inflammation
and necrosis.
4. The patient probably became infected by drinking water containing cysts.
5. The best course of treatment is metronidazole and rehydration.
CHAPTER 24 Microbial Diseases of the Urinary and
Reproductive Systems
Clinical Case Study: A Sick Mother-to-Be (p. 746)
1. The diagnosis is lymphogranuloma venereum, caused by Chlamydia trachomatis.
2. A baby passing through an infected birth canal may contract C. trachomatis infection of the
eyes (trachoma).
3. The mother can be treated with antibiotics such as erythromycin. Standard treatment for
exposed newborns is erythromycin cream applied to the eyes for up to two weeks to prevent
C. trachomatis infection from becoming established.
4. Untreated trachoma results in purulent discharge from the eyes, severe damage to the
conjunctiva, and inversion of the eyelids, eventually progressing to damage of the cornea
severe enough to result in blindness.
5. Untreated infection of the woman may progress to pelvic inflammatory disease, which may
result in sterility and/or ectopic pregnancy.
Clinical Case Study: A Case of Genital Sores (p. 747)
1.
2.
3.
4.
5.
The causative agent is Haemophilus ducreyi.
H. ducreyi produces a toxin that kills epithelial cells.
Women often have asymptomatic infections with H. ducreyi.
Chancroid is uncommon in the Americas, but is prevalent in Africa and Asia.
Chancroid can be treated with a variety of antibiotics, including azithromycin, erythromycin,
ceftriaxone, and ciprofloxacin.