Infectious Diseases

Infectious Diseases
13. What is the best time to treat PCP?
Before it happens! PCP is acquired when the CD4 count is below 200/mm3. At that point you
should institute PCP prophylaxis in an HIV-positive patient with trimethoprim-sulfamethoxazole.
Pentamidine is an alternative.
14. Cover the two right-hand columns and specify the organism after looking at the buzz
phrase associated with it:
SCENARIO BUG(S) COMMENTS
Stuck with thorn or gardening Sporothrix schenckii Treat with oral potassium
iodide or ketoconazole
Aplastic crisis in sickle cell diseaseParvovirus B19
Sepsis after splenectomy S. pneumoniae, H. influenzas, N.
meningitis (encapsulated bugs)
Pneumonia in the Southwest Coccidioides immitis Treat with itraconazole or
(California, Arizona) fluconazole, amphotericin
B for severe disease
Pneumonia after cave exploring orHistoplasma capsulatum
exposure to bird droppings in Ohio
and Mississippi River valleys
Pneumonia after exposure to Chlamydia psittaci
a parrot or exotic bird
Fungus ball/hemoptysis after Aspergillus sp. See figure
tuberculosis or cavitary
lung disease
Pneumonia in a patient with Tuberculosis
silicosis
Diarrhea after hiking/drinking Giardia lamblia Stool cysts; treat with
from a stream metronidazole
Pregnant woman with cats Toxoplasma gondii See figure
B]2 deficiency and abdominal Diphyllobothrium latum
symptoms
Seizures with ring-enhancing Taenia solium (cysticercosis) See figure
brain lesion on CT or toxoplasmosis
Squamous cell bladder cancer Schistosoma haematobium
in Middle East or Africa
Worm infection in children Enterobius sp. Positive tape test, perianal
itching
Fever, muscle pain, eosinophilia,Trichinella spirails (trichinosis)
and periorbital edema after
eating raw meat
Gastroenteritis in young childrenRotavirus, Norwalk virus
Food poisoning after eating Bacillus cereus
reheated rice
Food poisoning after eating Vibrio parahemolyticus
raw seafood
Diarrhea after travel to Mexico E. coli (Montezuma's revenge)
Diarrhea after antibiotics Clostridium difficile Use metronidazole or van-
comycin
Baby paralyzed after eating Clostridium botulinum Toxin blocks acetylcholine
honey release
Genital lesions in children in Molluscum contagiosum
the absence of sexual abuse
or activity
Table continued on next page



--------------------------------------- 26

Infectious Diseases 121
SCENARIO BUG(S) COMMENTS
Cellulitis after cat/dog bites Pasteurella muhocida Treat cat bites with
prophylactic ampicillin
Slaughterhouse worker with fever Brucellosis
Pneumonia after being in hotel Legionella pneumophila Treat with azithromycin or
or near air conditioner or levofloxacin
water tower
Burn wound infection with Pseudomonas sp. S. aureus is also a common
blue/green color burn infection, but it lacks
blue-green color
Ring-enhancing brain lesion. The differential is quite
broad for such findings; thus the clinical history is impor-
tant. In this case, which occurred as a complication of
acute myelogenous leukemia and immune compromise, a
biopsy yielded Aspergillus spp. (From Hoffbrand AV,
Pettit JE: Color Atlas of Clinical Hematology, 3rd ed. St.
Louis, Mosby, 2000, p 142, with permission.)
Acute toxoplasmosis. A thick peripheral blood
film shows trophozoite forms of Toxoplasma
gondii from a ruptured monocyte. (From Hoff-
brand AV, Pettit JE: Color Atlas of Clinical Hema-

€
•
15. How is syphilis diagnosed?
Screen for syphilis with a rapid plasma reagin (RPR) or Venereal Disease Research Labora-
tory (VDRL) test. Confirm a positive test with a fluorescent treponemal antibody absorbed (FTA-
ABS) or microhemagglutination (MHA-TP) test because false positives occur with the RPR and
VDRL tests, classically in patients with lupus erythematosus. Once syphilis is treated, the RPR
and VDRL tests become negative, whereas the FTA-ABS and MHA-TP tests often remain posi-
tive for life. You also can scrape the base of a genital chancre or condyloma lata and look for
spirochetes on dark-field microscopy.
16. Which group of patients should always be screened for syphilis?
Pregnant women. Early treatment can prevent birth defects.
17. How is syphilis treated?
With penicillin. Use doxycycline for penicillin-allergic patients.
18. Describe the three stages of syphilis.
Primary stage: look for painless chancre that resolves on its own within 8 weeks.
Secondary stage: roughly 6 weeks to 18 months after infection; look for condyloma lata,
maculopapular rash (classically involves palms and soles of feet), and lymphadenopathy.
Tertiary stage: years after initial infection (between the secondary and tertiary stages is the
latent phase, in which the disease is quiet and asymptomatic). Look for gummas (granulomas in
many different organs), neurologic symptoms and signs (e.g., neurosyphilis, Argyll-Robertson
pupil, dementia, paresis, tabes dorsalis, Charcot joints), and/or thoracic aortic aneurysms.
19. How do you recognize measles (rubeola) infection in a child?
Look for a reason for lack of immunization. Pathognomonic Koplik's spots (tiny white spots
on buccal mucosa) are seen 3 days after high fever, cough, runny nose, and conjunctivitis with or
without photophobia. On the next day, a maculopapular rash begins on the head and neck and
spreads downward to cover the trunk (cephalocaudal progression). Treat supportively.
20. Describe the complications of measles.
Complications include giant-cell pneumonia, especially in very young and immunocompro-
mised patients; otitis media; and encephalitis, either acute or late (subacute sclerosing panen-
cephalitis, which usually occurs years later).
21. Why is rubella infection (German measles) an important disease?
Rubella is important mainly because infection in pregnant mothers can cause severe birth
defects in the fetus. Screen and immunize all women of reproductive age without evidence of
rubella antibodies before pregnancy to avoid this complication. Remember, however, that the
vaccine is contraindicated in pregnant women.
22. How do you recognize a rubella infection in children? What are the complications?
Rubella is milder than measles. Signs and symptoms include low-grade fever, malaise, and
tender swelling of the suboccipital and postauricular nodes; arthralgias are common. After a 2- to 3-
day prodrome, a faint maculopapular rash appears on the face and neck and spreads to the trunk
(cephalocaudal progression), just as in measles. Complications include encephalitis and otitis media.
23. How do you recognize roseola infantum (exanthem subitum)? What causes it?
Roseola infantum is often easy to recognize because of the progression: high fever (may be
> 40° C) with no apparent cause for 4 days, which may result in febrile seizures, followed by an
abrupt return to normal temperature as a diffuse macular/maculopapular rash appears on the chest
and abdomen. The disease is rare in children older than 3 years. It is caused by the human her-
pesvirus type 6 (a DNA herpes family virus).
24. How do you recognize erythema infectiosum (fifth disease) in children? What causes it?
Look for the classic "slapped-cheek" rash (see figure, confluent erythema over the cheeks looks
like someone slapped the child across the face) accompanied by mild constitutional symptoms (e.g.,
low fever, malaise). One day later, a maculopapular rash appears on the arms, legs, and trunk. The
disease is caused by parvovirus B19, the same virus that causes aplastic crisis in sickle cell disease.
Erythema infectiosum. The blotchy erythema makes
it look as though the cheeks have been slapped.
(From du Vivier A: Atlas of Clinical Der
Infectious Diseases 123
25. How do you recognize chickenpox? What causes it?
The description and progression of the rash should lead you to the diagnosis: discrete mac-
ules (usually on the trunk) turn into papules, which turn into vesicles that rupture and crust over.
Such changes occur within 1 day. Because the lesions appear in successive crops, the rash will
be in different stages of progression in different areas. The cause is the varicella virus.
26. How can you make a definitive diagnosis of chickenpox? At what point is a patient with
chickenpox no longer infectious?
A Tzanck smear of tissue from the base of a vesicle shows multinucleated giant cells. A pre-
sumptive diagnosis can be made if the rash is classic. Infectivity ceases only when the last lesion
crusts over.
27. What are the complications of chickenpox?
A major complication is infection of the lesions with streptococci or staphylococci, which
causes erysipelas, cellulitis, and/or sepsis. The patient should be instructed to keep clean to avoid
infection. Other complications include pneumonia (especially in very young children, adults, and
immunocompromised patients), encephalitis, and Reye's syndrome. Do not give aspirin to a
child with a fever unless you have a diagnosis that requires its use. The varicella-zoster virus can
reactivate years later to cause herpes zoster (also known as shingles, see figure), a rash that devel-
ops in a dermatomal distribution, often with preceding pain and paresthesias. A child who has not
been immunized or exposed to chickenpox can catch the disease from someone with shingles.
Herpes zoster. Grouped vesicopustules are noted to
have a dermatomal distribution. (From du Vivier A:
Atlas of Clinical Dermatology, 3rd ed. New York,
Churchill Livingstone, 2002, p 7, with permission.)]
28. Describe the treatment and prophylaxis for chickenpox.
In most cases, no treatment is needed except supportive care (e.g., acetaminophen, fluids,
avoidance of infecting others). Acyclovir can be used in severe cases. Routine vaccination with
the varicella vaccine is now recommended for all children in the United States. Varicella-zoster
immunoglobulin is available for prophylaxis in patients with debilitating illness (e.g., leukemia,
AIDS) if you see them within 4 days of exposure and for newborns of mothers with chickenpox.
29. What is scarlet fever? What causes it? How is it recognized and treated?
Scarlet fever is a febrile illness with a rash caused by certain Streptococcus species. Look for
a history of untreated streptococcal pharyngitis; only streptococcal species that produce erythro-
genic toxin can cause scarlet fever. Pharyngitis is followed by a sandpaper-like rash on the
abdomen and trunk with classic circumoral pallor and strawberry tongue. The rash tends to
desquamate once the fever subsides. Treat streptococcal pharyngitis with penicillin to prevent
rheumatic fever.
30. What are the diagnostic criteria for Kawasaki's syndrome (mucocutaneous lymph node
syndrome)?
This rare disease is seen in patients under 5 years old on the Step 2 exam. The diagnostic cri-
teria include fever for more than 5 days (mandatory for diagnosis); bilateral conjunctival injec-
tion; changes in the lips, tongue, or oral mucosa (e.g., strawberry tongue, fissuring, injection);
changes in the extremities (e.g., skin desquamation, edema, erythema); polymorphous truncal
rash, which usually begins one day after the fever starts; and cervical lymphadenopathy. Also
look for arthralgia or arthritis.
31. What is the most feared complication of Kawasaki's disease? How do you prevent it?
The most feared complications involve the heart (coronary artery aneurysms, congestive
heart failure, arrhythmias, myocarditis, and even myocardial infarction). Include Kawasaki's syn-
drome in the differential diagnosis of any child who has a myocardial infarction. If Kawasaki's
disease is suspected, give aspirin and intravenous immunoglobulins. Both have been proved to
reduce cardiac lesions. Kawasaki's disease is one of the few indications for aspirin in a child.
Follow the child with echocardiography to detect heart involvement.
32. Describe the classic findings of Epstein-Barr virus (EBV) infection (infectious mono-
nucleosis).
Look for fatigue, fever, pharyngitis, and cervical lymphadenopathy in a young adult. The
signs and symptoms are similar to those of streptococcal pharyngitis, but malaise tends to be pro-
longed and pronounced in EBV infection. To differentiate from streptococcal pharyngitis, look
for the following:
• Splenomegaly (patients may have splenic rupture and should avoid contact sports and
heavy lifting)
• Hepatomegaly
• Atypical lymphocytes (bizarre forms that may resemble leukemia) with lymphocytosis,
anemia, or thrombocytopenia
• Positive serology (heterophile antibodies [e.g., Monospot test] or specific EBV antibodies
(viral capsid antigen, Epstein-Barr nuclear antigens).
33. What is an important differential diagnosis of EBV infection?
Acute HIV infection, which can cause a mononucleosis-type syndrome.
34. What is the association between EBV and cancer?
EBV is associated with nasopharyngeal cancer, African Burkitt's lymphoma, and posttrans-
plant lymphoproliferative disorder.
35. Describe the classic clinical vignette for Rocky Mountain spotted fever. What causes it?
What is the treatment?
Look for history of a tick bite (especially in a patient on the East Coast) one week before the
development of high fever/chills, severe headache, and prostration or severe malaise. A rash
appears roughly 4 days later on the palms/wrists and soles/ankles and spreads rapidly to the trunk
and face (unique pattern of spread). Patients often look quite ill (e.g., disseminated intravascular
coagulation, delirium). The infection is caused by Rickettsia rickettsii. Treat with tetracycline;
chloramphenicol is a second choice.
36. How do you recognize and treat the rash of impetigo?What causes it?
In patients with impetigo, which is caused by Streptococcus and Staphylococcus species,
look for a history of a break in the skin (e.g., previous chickenpox, insect bite, scabies, cut). The
rash starts as thin-walled vesicles that rupture and form yellowish crusts. The skin classically is
described as "weeping." Typical lesions appear on the face and tend to be localized. The rash is
infectious; look for a history of sick contacts. Treat with an oral antistaphylococcal penicillin
(e.g., methicillin) to cover both Streptococcus and Staphylococcus species.
37. Describe the two clinical types of endocarditis. What are the causative bugs?
1. Acute (fulminant) endocarditis, which typically affects normal heart valves and most
commonly is caused by Staphylococcus aureus.
2. Subacute, which has an insidious onset and typically affects previously damaged or
mechanical valves. The most common cause is Streptococcus viridans, but other strepto
and staphylococcal species also may cause endocarditis (e.g., Staphylococcus epidermis, Strep-
tococcus bovis, and Streptococcus faecalis [also known enterococci]). Suspect colon cancer if S.
bovis turns up on blood culture.
38. How is endocarditis diagnosed and treated?
The diagnosis generally is made by blood cultures. Empiric treatment is begun with broad-
spectrum intravenous antibiotics until the culture and sensitivity results are known. A third-gen-
eration penicillin or cephalosporin plus an aminoglycoside is a reasonable choice.
39. What are the classic signs and symptoms of endocarditis?
Look for general signs of infection (e.g., fever, tachycardia, malaise) plus new-onset heart
murmur, embolic phenomena (stroke and other infarcts), Osier's nodes (painful nodules on tips
of fingers), Janeway lesions (nontender, erythematous lesions on palms and soles), Roth spots
(round retinal hemorrhages with white centers), and septic shock (more likely with acute than
subacute disease).
40. What elements of the history point to endocarditis?
Look for patients who are more likely to be affected by endocarditis:
• Intravenous drug abusers, who usually have right-sided lesions, although left-sided lesions
are much more common in the general population.
• Patients with abnormal heart valves (e.g., prosthetic valves, rheumatic valvular disease,
congenital heart defects such as ventricular septal defects or tetralogy of Fallot).
• Postoperative patients (especially after gastrointestinal, genitourinary, or dental surgery).
41. What are the recommendations for endocarditis prophylaxis?
Any person with known heart valve disease should be given oral amoxicillin before and after
dental procedures to cover S. viridans. Substitute clindamycin or azithromycin for penicillin-
allergic patients. For gastrointestinal or genitourinary procedures, give intravenous ampicillin
and gentamicin before and amoxicillin after the procedure. If the patient is allergic to penicillin,
substitute vancomycin. Patients with secundum-type atrial septal defects (the more common
type) or patients with mitral valve prolapse and no audible murmur do not require endocarditis
prophylaxis.
42. What is the classic age group for meningitis? Describe the physical findings.
Neonates are the classic age group for meningitis; 75% of all cases occur in children younger
than 2 years. Deciding when to do a lumbar tap is difficult, because patients often do not have
classic physical findings (Kernig's and Brudzinski's signs). Look for lethargy, hyper- or
hypothermia, poor muscle tone, bulging fontanelle, vomiting, photophobia, altered conscious-
ness, and signs of generalized sepsis (e.g., hypotension, jaundice, respiratory distress). Seizures
also may be seen, but simple febrile seizures are common if the patient is between 5 months and
6 years old and has a fever > 102° F without other signs of meningitis.
43. What should you do if you suspect meningitis?
In the absence of trauma, do a lumbar puncture immediately and begin broad-spectrum
antibiotics and IV fluids. Do not wait for culture or other results to start antibiotics.
44. What is the most common neurologic sequela of meningitis?
Hearing loss. All pediatric and many adult patients need formal hearing evaluation after a
bout of meningitis. Vision testing also is recommended. Other sequelae include mental retarda-
tion, motor deficits/paresis, epilepsy, and learning/behavioral disorders.
45. What are the common viral (aseptic) causes of meningitis in children?
Mumps and measles meningitis may be seen in children who are not immunized. The best
treatment is prevention via immunization. Watch for neonatal herpes encephalitis (HSV-2) if the

• 126 Infectious Diseases
mother has genital lesions of herpes simplex virus at the time of delivery. Other children and
adults can develop HSV-1 herpes encephalitis, which classically affects the temporal lobes on a
head CT or MR scan. Give intravenous acyclovir.
46. Which types of bacterial meningitis require antibiotic prophylaxis in contacts?
N. meningitidis and H. influenzae. If a case of meningitis is due to Neisseria, give all contacts
rifampin or ciprofloxacin as prophylaxis; rifampin is used for H. influenzae meningitis prophylaxis.
47. What are the "big three" respiratory infections in patients younger than 5 years?
Croup, epiglottitis, and respiratory syncytial virus infection (bronchiolitis). These three dis-
eases are high yield on the USMLE.
48. How do you recognize croup (acute laryngotracheitis)? Describe the cause and
treatment.
Look for a child 1-2 years of age. Croup usually occurs in the fall or winter. Fifty to 75% of
cases are due to infection with parainfluenza virus; the other causative agent is influenza virus.
The disease begins with symptoms of viral upper respiratory infection (e.g., rhinorrhea, cough,
fever). Roughly 1-2 days later patients develop a "barking" cough, hoarseness, and inspiratory
stridor. The "steeple sign" (describes subglottic narrowing of the trachea) is classic on a frontal
radiograph of the chest or neck. Treat supportively with a mist tent, humidified oxygen, and
racemic epinephrine.
49. How do you recognize epiglottitis? Describe the cause and treatment.
Epiglottitis usually occurs in children 2-5 years old. The main cause is Haemophilus influen-
zae type b, thus widespread vaccination has significantly reduced the incidence of this condition.
Staphylococcus aureus, S. pyogenes and S. pneumoniae are other potential causes. Look for little
or no prodrome, with rapid progression to high fever, toxic appearance, drooling, and respiratory
distress with no coughing. The "thumb sign" (describes a swollen, enlarged epiglottis) is classic
on lateral radiographs of the neck. Do not examine the throat or irritate the child in any way. You
may precipitate airway obstruction. When a case of epiglottitis is diagnosed, the first step is to be
prepared to establish an airway (intubation and, if needed, tracheostomy). Treat with antibiotics
(e.g., third-generation cephalosporin).
50. Describe the classic clinical vignette for bronchiolitis. What is the cause? How is it
treated?
Bronchiolitis generally affects children aged 0-18 months and usually occurs in the fall or
winter. More than 75% of cases are caused by respiratory syncytial virus (RSV); other causes are
parainfluenza and influenza viruses. Patients first develop symptoms of viral upper respiratory
infection, followed 1-2 days later by rapid respirations, intercostal retractions, and expiratory
wheezing. The child may have crackles on auscultation of the chest. Diffuse hyperinflation of the
lungs is classic on chest radiograph; look for flattened diaphragms. Treat supportively (e.g.,
oxygen, mist tent, bronchodilators, intravenous fluids). Use ribavarin in patients with severe
symptoms or at high risk (e.g., patients with cyanosis or other chronic health problems).
51. What "old-school" pediatric infection causes pseudomembranes and myocarditis?
What about whooping cough?
Diphtheria (Corynebacterium diphtheriae) and pertussis (Bordetella pertussis), respectively.
Both are quite uncommon in the U.S. because of mandatory vaccination. If a child is unimmu-
nized (e.g., child of immigrants), don't forget these two entities. Diphtheria causes grayish
pseudomembranes (necrotic epithelium and inflammatory exudate) on the pharynx, tonsils, and
uvula as well as myocarditis. Pertussis is associated with severe paroxysmal coughing and a high-
pitched whooping inspiratory noise (traditionally called "whooping cough"). Treat both with
erythromycin, and give antitoxin for diphtheria
52. In what clinical scenario does rabies occur in the U.S.? Describe the classic physical
findings.
Rabies in the U.S. is due to bites from bats, skunks, raccoons, or foxes; vaccination has elim-
inated rabies due to dog bites. The incubation period is usually around 1-2 months. The classic
findings are hydrophobia (fear of water due to painful swallowing) and central nervous system
signs (e.g., paralysis).
53. What should you do after a patient is bitten by an animal?
1. Treat the local wound. Cleanse thoroughly with soap. Do not cauterize or suture the
wound. Ampicillin or amoxicillin is often given for cellulitis prophylaxis.
2. Observe the animal. If possible, capture and observe the dog or cat to see if it develops
rabies. If a wild animal is caught, it should be killed and the brain tissue examined for rabies.
3. If the wild animal escapes or has rabies, give rabies immunoglobulin and vaccinate the
patient. In cases of a dog or cat bite, do not give prophylaxis or vaccine unless the animal acted
strangely or bit the patient without provocation and rabies is prevalent in the area (rare). Do not
give prophylaxis or vaccine for rabbit or rodent bites (e.g., rats, mice, squirrels, chipmunks).
54. What are the two main infections caused by Streptococcus pyogenes (group A strepto-
cocci)? What are the common sequelae?
S. pyogenes causes pharyngitis and skin infections. Sequelae include rheumatic fever, scar-
let fever, and poststreptococcal glomerulonephritis.
55. How does streptococcal pharyngitis present? How do you diagnosis and treat it?
Look for sore throat with fever, tonsillar exudate, enlarged tender cervical nodes, and leuko-
cytosis. A positive streptococcal throat culture confirms the diagnosis. Elevated liters of anti-
streptolysin O (ASO) and anti-DNase antibody can be used for a retrospective diagnosis in
patients with rheumatic fever or poststreptococcal glomerulonephritis. Treat streptococcal
pharyngitis with penicillin to avoid rheumatic fever and scarlet fever.
56. What are the major and minor Jones criteria for rheumatic fever? Why is rheumatic
fever less common today?
The five major Jones criteria include migratory polyarthritis, carditis, chorea, erythema mar-
ginatum, and subcutaneous nodules. The minor Jones criteria include elevations in erythrocyte
sedimentation rate, C-reactive protein, white blood cell count, and ASO liter; prolonged PR inter-
val on EKG; and arthralgia. The diagnosis of rheumatic fever requires a history of streptococcal
pharyngitis plus at least one major criterion. Trealment of slreptococcal pharyngitis wilh antibi-
otics markedly reduces ihe incidence of rheumatic fever; thus, it is less common today. Give all
palienls affected by rheumatic fever endocarditis prophylaxis before surgical procedures.
57. How do you recognize poststreptococcal glomerulonephritis? How is it treated?
Postslreptococcal glomerulonephritis occurs most commonly after a streptococcal skin
infection, but it also may occur after pharyngitis. Palienls are usually children and generally pres-
enl wilh a history of infection wilh a nephrilogenic slrain of Streptococcus species 1-3 weeks ear-
lier and abrupl onsel of hemaluria, proleinuria (mild, nol in nephrolic range), red blood cell casts,
hypertension, edema (especially periorbilal), and elevated blood urea nilrogen/crealinine. Treal
supporlively. Conlrol blood pressure, and use diuretics for severe edema. Trealmenl of strepto-
coccal infections does nol reduce Ihe incidence of poslslreptococcal glomerulonephritis.
58. Distinguish between impetigo and erysipelas.
Bolh are superficial skin infections due lo streptococci or S. aureus and often occur after a
break in the skin (e.g., trauma, scabies, insect bile). Impetigo classically changes first from mac-
ulopapules to vesicopustules and bullae and Ihen to honey-colored, crusted lesions. Slaphylo-
cocci are a more frequenl cause than slreplococci. Definitely think of slaphylococci if a furuncle


128 Infectious Diseases
or carbuncle is present; think of streptococci if glomerulonephritis develops. Impetigo is conta-
gious; watch for sick contacts. Erysipelas is a superficial cellulitis that appears red, shiny, and
swollen; it is tender and may be associated with vesicles and bullae, fever, and lymphadenopa-
thy. Treat both empirically with an antistaphylococcal penicillin (e.g., dicloxacillin).
59. What organisms typically cause cellulitis? What special circumstances should make
you think of atypical causes?
Streptococci and staphylococci cause most cases. Think of Pseudomonas species with burns
or severe trauma; of Pasteurella multocida after dog or cat bites (treat with ampicillin); of Vibrio
vulnificus in fishermen or other patients exposed to salt water (treat with tetracycline). Diabetic
patients with foot ulcers tend to have polymicrobial infections and need powerful, broad-spec-
trum antibiotic coverage.
60. Describe the physical findings of cellulitis. Define necrotizing fasciitis. How is it treated?
In patients with cellulitis, the involved overlying skin is red, hot, and frequently tender. It
looks like erysipelas but involves deeper subcutaneous tissues. Treat with anti-staphylococcal
antibiotics to cover both strep and staph. Necrotizing fasciitis is defined as the progression of cel-
lulitis to necrosis and gangrene. Watch for crepitus and signs of systemic toxicity (e.g., tachy-
cardia, fever, hypotension). Often multiple organisms are involved (aerobes and anaerobes). Treat
with intravenous fluids, incision and drainage/surgical debridement, and broad-spectrum antibi-
otics (e.g., broad-spectrum penicillin or cephalosporin plus an aminoglycoside).
61. What is the most common cause of endometritis (puerperal fever)? How do you recog-
nize and treat it?
Watch for endometritis, an infection of the endometrial lining, as a cause of postpartum
fever. The hallmark is uterine tenderness, and the most common cause is Streptococcus species.
Treat with amoxicillin or ampicillin after getting local cultures.
62. What infection in neonates is caused by Streptococcus agalactiae (group B streptococci)?
Streptococcus agalactiae is the most common cause of neonatal meningitis or sepsis. The
organism is often part of normal vaginal flora and may be acquired from the birth canal. Group
B streptococci are penicillin-sensitive. Expectant mothers are cultured for S. agalactiae, and if it
is present around the time of delivery, prophylactic penicillin or ampicillin is given to the mother
to prevent meningitis in the newborn.
63. Other than pneumonia, what infections does Streptococcus pneumoniae commonly cause?
Otitis media, meningitis, sinusitis, and spontaneous bacterial peritonitis.
64. What are the main infections caused by S. aureus"!
The list is long. S. aureus is a common cause of the following infections:
• Skin and soft-tissue abscesses (especially in the breast after breast-feeding or in the skin
after a furuncle)
• Endocarditis (especially in drug users)
• Osteomyelitis (the most common cause unless sickle cell disease is present)
• Septic arthritis
• Food poisoning (via a preformed toxin)
• Toxic shock syndrome (via a preformed toxin)
• Scalded skin syndrome (via a preformed toxin; affects younger children who often present
with impetigo, then desquamate; see figure)
• Impetigo
• Cellulitis
• Wound infections
• Pneumonia (often forms lung abscess or empyema)
• Furuncles and carbuncles

Staphylococcal scalded skin syndrome. The skin
is typically raw and desquamates in sheets. (From
du Vivier A: Atlas of Clinical Dermatology, 3rd
ed. New York, Churchill Livingstone, 2002, p
252, with permission.)
65. Who are the classic spreaders of nosocomial Staphylococcal infections?
Health care workers who are chronic nasal carriers can cause nosocomial infections. Carri-
ers should be treated with antibiotics.
66. What is the treatment of choice for Staphylococcal infections on the USMLE?
An antistaphylococcal penicillin (e.g., methicillin, dicloxacillin). Use vancomycin in patients
with penicillin allergy or if the Staphylococcal species is known to be methicillin-resistant. Methi-
cillin-resistant S. aureus (MRSA) is a growing problem. Most abscesses (regardless of the
causative organism) must be treated first with surgical incision and drainage because antibiotics
cannot penetrate through the walls of an abscess cavity.
67. Cover up the right-hand column in the table below and describe the preferred treat-
ment for tuberculosis based on the clinical scenario.
CLINICAL SETTING/FINDINGS TREATMENT
Exposed adult with negative PPD skin test None
Exposed child < 5 years old with negative PPD Isoniazid (INH) for 3 mo
Prophylaxis for PPD conversion (negative to positive),INK for 6-12 mo
no active disease
Active pulmonary disease/positive culture INH/rifampin/pyrazinamide for 2 mo,
then INH/rifmapin for 4 mo
PPD = purified protein derivative.
Other important tuberculosis treatment issues:
• Multidrug resistant strains an increasing problem and requires the addition of streptomycin
or ethambutol until sensitivities are known.
• If the patient is noncompliant, directly observed therapy (someone watches the patient take
medications every day) is recommended.
• Consider supplementation with vitamin B 6 (pyridoxine) for patients on isoniazid (INH), or
watch for signs of deficiency.
• Watch for liver dysfunction in patients on therapy.