Chapter 7 - ID

Question 1

Which organisms are most likely to cause serious bacterial illness, namely sepsis or meningitis, in the following age groups and what are the empiric antibiotics of choice based on this?

• 0 to 1 month
• 1 to 3 months
• 3 to 36 months
• 3 years and older

Answer 1

• 0-1 month: GBS, E. coli, Listeria - treat with ampicillin + gentamicin or cefotaxime
• 1-3 months: GBS, S. pneumoniae, Listeria - treat with ampicillin + cefotaxime + vancomycin if bacterial meningitis is suspected
• 3-36 months: S. pneumoniae, H. influenza type b, N. meningitidis - treat with cefotaxime + vancomycin if bacterial meningitis is suspected
• older: S. pneumoniae, N. meningitidis - treat with cefotaxime + vancomycin if bacterial meningitis is suspected

Question 2

What is fever of unknown origin?

Answer 2

a fever lasting longer than 8 days to 3 weeks without a primary diagnosis

Question 3

Bacterial Meningitis

Answer 3

• risk factors are young age, especially in the first month of life, immunodeficiency, and anatomic defects
• GBS, E. coli, Listeria, S. pneumoniae, H. influenzae type b, and N. meningitidis are the most common organisms depending on age
• infants and young children may have nonspecific signs with an absent or minimal fever and bulging fontanelle
• older children often present with fever, altered consciousness, nuchal rigidity, seizures, photophobia, emesis, and headache
• children with suspected bacterial meningitis should receive a lumbar puncture, blood culture, and CT scan with contrast to evaluate for brain abscesses
• CSF culture may be sterile if antibiotics have been started, but the biochemical profile should be unchanged
• elevated WBC with predominately PMNs, high protein, low glucose, and a positive culture/gram stain
• treat with empiric antibiotics based on age and likely organism, corticosteroids to reduce the incidence of hearing loss in HIB meningitis, and supportive care
• most often complicated when due to a gram-negative or S. pneumoniae; may be complicated by hearing loss, global brain injury, SIADH, seizures, hydrocephalus etc.

Question 4

What are the primary complications of bacterial meningitis?

Answer 4

• hearing loss
• global brain injury
• SIADH
• seizures
• hydrocephalus

Question 5

Describe the CSF profile in someone with the following types of meningitis:

• acute bacterial
• partially treated bacterial
• viral
• tuberculosis
• fungal
• parameningeal focus

Answer 5

• acute bacterial: elevated WBC with predominately PMNs, high protein, low glucose, and positive culture/stain
• partially treated bacterial: elevated WBC with predominately monocytes, normal to high protein, low glucose, and a negative culture/stain
• viral: PMNs early, then monocytes and lymphocytes, normal to high protein, normal glucose; enterovirus may be cultured, HSV encephalitis may show RBCs
• tuberculosis: slightly elevated WBC with predominately lymphocytes, very high protein content, low glucose
• fungal: slightly elevated WBC with predominately lymphocytes
• normal to high protein, low glucose

Question 6

Aseptic Meningitis

Answer 6

• inflammation of the meninges with a CSF lymphocytic pleocytosis
• viral meningitis is the most common form with enteroviruses being the predominate agent
• clinical features resemble bacterial meningitis with fever, altered consciousness, nuchal rigidity, seizures, photophobia, emesis, and headache
• typically CSF WBC is elevated but to a lesser extent than in bacterial cases and there are predominately PMNs early but then monocytes and lymphocytes; protein is normal or high and glucose is normal
• most cases are self-limited and require only supportive therapy

Question 7

M. tuberculosis Meningitis

Answer 7

• an aseptic bacterial meningitis
• most common in children younger than 5 years old
• presents with lethargy or irritability which progresses rapidly to cranial nerve deficits, altered consciousness, coma, paraplegia, and death
• has a slightly elevated WBC with predominately lymphocytes, protein is high, and glucose is low
• likely to find a characteristic basilar enhancement on neuroimaging and a positive culture or PCR
• treated with RIPE therapy

Question 8

Simple Upper Respiratory Infection

Answer 8

• also known as the common cold, which can be caused by a number of viruses including rhinovirus, parainfluenza, and coronavirus
• presents with low-grade fever, rhinorrhea, cough, and sore throat, which resolve within 7-10 days; persistent symptoms beyond 10 days warrant evaluation for bacterial superinfection
• treat with hydration and exclusion of more serious disorders

Question 9

Describe development of the sinuses.

Answer 9

• the ethmoid and maxillary sinuses are present at birth
• the sphenoid sinuses develop between 3-5 years of age
• frontal sinuses arise between 7-10 years of age

Question 10

Sinusitis

Answer 10

• most often caused by S. pneumoniae, H. influenzae, or M. catarrhalis
• clinical features help classify it as acute persistent, acute severe, subacute, or chronic
• acute severe presents with purulent nasal discharge for 3-5 days and has a high fever
• acute persistent presents with nasal discharge and cough for 10-30 days and may also have headache, malodorous breath, facial pain, or low-grade fever
• subacute has these same symptoms for 30-90 days and chronic lasts more than 90 days
• chronic should be evaluated for an underlying condition like CF or involvement of S. aureus or an anaerobe
• acute and subacute are treated with amoxicillin, amoxicillin-clavulanate, or second generation cephalosporin for 10-14 days
• chronic is typically treated with a trial of broad-spectrum oral antibiotics and CT imaging

Question 11

Viral Pharyngitis

Answer 11

• there are many causes including those involved in simple URI
• presents with low-grade fever, rhinorrhea, cough, and sore throat in addition to tonsils exudates
• specifically, EBV pharyngitis may present with enlarged posterior cervical lymph nodes, malaise, and hepatosplenomegaly; coxsackievirus pharyngitis presents with herpangina
• managed with supportive care, analgesics, and maintenance of adequate hydration; EBV pharyngitis may require corticosteroids

Question 12

Strep Pharyngitis

Answer 12

• caused by S. pyogenes (GABHS)
• presents with a lack of other URI symptoms, petechiae on the soft palate, strawberry tongue, and enlarged tender anterior cervical lymph nodes, fever, and scarlatiniform rash
• culture is the gold standard for diagnosis but is slow so antigen testing is a common substitute in the short-term
• treated with oral penicillin, single dose IM penicillin, or oral erythromycin or macrolides

Question 13

Corynebacterium diphtheriae

Answer 13

• gram positive rods which are club-shaped, contain metachromatic granules, and form V or Y shapes
• spread via respiratory droplets, colonize the oropharynx, and may spread in the blood
• they produce an extoxin encoded by beta-prophage, which ADP-ribosylates and inactivates EF-2, inhibiting protein production by host cells
• the bacteria cause “bull neck” lymphadenopathy, pseudomembrane formation in the oropharynx, a potentially fatal myocarditis with heart block and arrhythmia, and nerve deficits beginning in the posterior pharyngeal wall
• diagnosis is made by culture on cystine-tellurite or Loeffler’s medium in combination with the Elek’s test to distinguish toxigenic species from nontoxigenic ones
• treated with oral erythromycin or parenteral penicillin
• toxoid vaccine is available (DTaP)

Question 14

Acute Otitis Media

Answer 14

• an acute infection of the middle ear space
• most commonly caused by S. pneumoniae, non-tapeable H. influenzae, or Moraxella catarrhalis
• presents with fever, ear pain, and decreased hearing; there may be drainage if the tympanic membrane perforates
• diagnosis requires identification of fluid in the middle ear space with symptoms; fluid is most reliably detected using a pneumatic otoscope since erythema and loss of tympanic membrane landmarks are unreliable
• treated with amoxicillin, amoxicillin-clavulanic acid, or cephalosporin

Question 15

What is an otitis media with effusion?

Answer 15

defined as fluid within the middle ear space without symptoms of infection

Question 16

Otitis Externa

Answer 16

• risk factors are those that interfere with the protective mechanisms of the outer ear: cerumen removal, trauma, maceration of the skin from swimming, or excessive moisture
• P. aeruginosa, S. aureus, and Candida albicans are the most common organisms
• presents with pain, tenderness on palpation or movement of the tragus, itching, and drainage; systemic symptoms are usually absent
• diagnosis is based on erythema and edema of the external auditory canal
• treated with restoration of the canal’s acidic environment: use acetic acid solution for mild cases and add topical antibiotics for more severe cases
• if a perforated AOM is complicated by OE, treat with both oral and topical antibiotics

Question 17

Cervical Lymphadenitis

Answer 17

• present as enlarged, tender, warm, and mobile nodes with overlying erythema in the cervical area
• S. aureus is the most common bacterial agent but S. pyogenes, mycobacterium, and B. henselae are also seen
• other causes include reactive lymphadenitis, viral lymphadenitis, Kawasaki disease, or T. gondii
• managed with empiric antibiotics directed toward S. aureus and S. pyogenes, including a first-generation cephalosporin or anti-staph penicillin

Question 18

What is cervical reactive lymphadenitis?

Answer 18

an enlarged, inflamed, tender lymph node in the cervical area that occurs in response to infections of the pharynx, teeth, or soft tissues of the head and neck

Question 19

What typically distinguishes Kawasaki disease-related lymphadenitis from other causes?

Answer 19

Kawasaki disease usually presents with unilateral cervical lymphadenitis rather than bilateral

Question 20

Parotitis

Answer 20

• an inflammation of the parotid salivary glands
• bilateral cases are usually caused by mumps and other viruses while bacterial parotitis caused by S. aureus, S. pyogenes, and M. tuberculosis result in unilateral parotitis
• presents with swelling centered above the angle of the jaw, fever, and sometimes pus expressed from Stensen’s duct
• diagnosed based on culture from the Stensen’s duct drainage in the case of bacterial parotitis and by viral serology in viral parotitis
• treated with supportive care, analgesics, and antibiotics if bacterial
• may be complicated by meningoencephalitis, orchitis, epididymitis, or pancreatitis as well as abscess and osteomyelitis of the jaw

Question 21

Impetigo

Answer 21

• a superficial infection of the upper dermis
• usually caused by S. aureus or GABHS
• presents with lesions that have a honey-colored crust; fever is generally absent
• treated with topical mupirocin or oral antibiotics
• may be complicated by post-streptococcal glomerulonephritis or staphylococcal scalded skin syndrome depending on the offending organism

Question 22

Erysipelas

Answer 22

• an infection of the dermal lymphatics
• usually caused by GABHS
• presents with tender, erythematous skin that has a distinct border
• treated with antibiotics directed at GABHS
• may be complicated by bacteremia, post-streptoccal glomerulonephritis, and necrotizing fasciitis

Question 23

Cellulitis

Answer 23

• a skin infection that occurs within the dermis
• caused by GABHS and S. aureus, usually following a break in the skin
• presents as an erythematous, warm, tender area that has an indistinct border
• diagnosed by visual inspection and blood cultures are seldom positive; culture of biopsy can be performed if aggressive
• treated with first generation cephalosporins or anti-staphylococcal penicillins

Question 24

How is erysipelas differentiated from cellulitis?

Answer 24

erysipelas is a lesion with distinct borders whereas cellulitis has indistinct borders

Question 25

Buccal Cellulitis

Answer 25

• an uncommon variant of cellulitis
• presents with a fever and unilateral bluish discoloration of the cheek in young, unimmunized children
• caused by type b H. influenzae
• treated with second or third generation cephalosporin
• there is a high rate of concomitant bacteremia and meningitis, so a lumbar puncture should be performed

Question 26

Perianal Cellulitis

Answer 26

• a variant of cellulitis
• caused by GABHS
• presents with a well-demarcated erythematous lesion around the anus; may also have constipation
• treated with oral antibiotics

Question 27

Necrotizing Fasciitis

Answer 27

• a potentially fatal form of deep cellulitis
• typically polymicrobial
• presents with pain and systemic symptoms out of proportion to the physical findings
• requires IV antibiotics and surgical debridement of the affected area

Question 28

Staphylococcal Scalded Skin Syndrome

Answer 28

• a variant of cellulitis caused by S. aureus species that produce an exfoliative toxin
• presents with fever, tender skin, and bullae; large sheets of skin slough and there is a positive Nikolsky sign
• treat with good wound care and IV antibiotics

Question 29

Scarlet Fever

Answer 29

• a toxin-mediated bacterial illness presenting with a characteristic skin rash
• caused by GABHS, which produce an erythrogenic toxin, and transmitted via large respiratory droplets
• presents with fever, chills, malaise, and exudative pharyngitis before or during the exanthem
• the exanthem begins on the trunk, is erythematous with tiny skin-colored papules, blanches, has a texture of sandpaper, has localized petechiae in a linear distribution, and involves desquamation of dry skin
• diagnosed according to clinical features and a positive throat culture for S. pyogenes
• treated with penicillin
• may be complicated by post-strep glomerulonephritis, rheumatic fever, post-strep arthritis, or pediatric autoimmune neuropsychiatric disorders associated with Streptococcal infection

Question 30

What is post-streptococcal arthritis?

Answer 30

joint symptoms without the other features of rheumatic fever which follow GABHS infection and last for weeks

Question 31

What is pediatric autoimmune neuropsychiatric disorders associated with Streptococcal infection?

Answer 31

the acute onset of obsessive-compulsive symptoms shortly after a streptococcal infection, which can be prevented with penicillin during the initial infection

Question 32

Toxic Shock Syndrome

Answer 32

• a toxin-mediated illness most often caused by S. aureus but also by GABHS
• diagnosis requires 5 of the following 6: fever higher than 38.5, hypotension, diffuse macular erythroderma, desquamation occurring 10-14 days after onset of the illness, multisystem involvement of 3 or more systems, and negative cultures of blood, CSF, and pharynx
• historically caused by S. aureus in young women who left in tampons for a prolonged period of time
• treated with supportive therapy, anti-staphylococcal antibiotics, and removal of the nidus

Question 33

Rotavirus

Answer 33

• an RNA virus spread via the fecal-oral route, most commonly seen during the winter months
• it is the most common infectious agent causing gastroenteritis
• presents with vomiting, diarrhea, and dehydration lasting 4-7 days
• diagnosed based on stool ELISA; WBCs are absent from stool
• treatment is supportive
• may be complicated by a post-infection transient lactose intolerance

Question 34

Norwalk Virus

Answer 34

• an RNA virus spread via the fecal-oral route, most commonly seen in closed populations
• presents as gastroenteritis with predominately vomiting, which lasts 2-3 days
• treatment is supportive

Question 35

ETEC

Answer 35

• a lactose-fermenting, encapsulated, catalase-positive, gram-negative, which forms green colonies on EMB agar
• commonly referred to as traveler’s diarrhea and found in contaminated water sources, usually in developing nations
• utilizes a heat-labile enterotoxin, which increases cAMP, and a heat-stable enterotoxin, which increases cGMP, to cause a non-invasive, watery diarrhea
• WBCs are absent from the stool and it is a clinical diagnosis
• treat with quinolones or sulfonamides to shorten the duration while maintaining hydration

Question 36

Enteropathogenic E. coli (EPEC)

Answer 36

• a lactose-fermenting, encapsulated, catalase-positive, gram-negative, which forms green colonies on EMB agar
• presents as noninvasive, water diarrhea
• WBCs are absent in stool and diagnosis is made via culture
• treat with oral quinolones or sulfonamides while maintaining hydration status

Question 37

Enterohemorrhagic E. coli (EHEC)

Answer 37

• a lactose-fermenting, encapsulated, catalase positive gram-negative, which forms green colonies on EMB agar
• unique in that they do not ferment sorbitol like most other species of E. coli
• commonly contaminates undercooked meats and O157:H7 is the most important serotype
• utilize a shiga-like toxin which inhibits the 60S ribosomal subunit and thus cause bloody diarrhea as well as HUS
• WBCs can be found in stool and culture is diagnostic
• avoid antibiotics if HUS is present

Question 38

Shigella sonnei

Answer 38

• an immotile, acid-stable, facultative intracellular, gram-negative bacillus, which forms green colonies on Hektoen enteric agar, differentiating it from salmonella
• taken up by M cells and spread via actin-rockets, using a T3SS and shiga toxin to inhibit the 60S ribosomal subunit of host cells
• causes an inflammatory, bloody diarrhea usually in children under 10 years old
• WBCs are present in stool and culture is diagnostic
• may be complicated by HUS or seizures secondary to neurotoxin release
• treat with third-generation cephalosporins or fluoroquinolones

Question 39

Salmonella spp.

Answer 39

• a bacterial cause of diarrhea, which can be bloody or nonbloody
• spread via the fecal-oral route, poultry, milk, eggs, and exposure to lizards or turtles
• WBCs may be present or absent in stool and culture is diagnostic
• treatment is not indicated for uncomplicated cases in hosts older than three months; invasive disease should be treated with a third-generation cephalosporin
• patients with sickle cell disease may develop bacteremia or osteomyelitis

Question 40

Campylobacter jejuni

Answer 40

• an oxidase positive, curved, gram-negative rod
• thermophilic and prefers to grow at 42 degrees Celsius
• contaminates poultry and causes a bloody diarrhea
• WBCS are usually present if blood is present
• can be treated with oral erythromycin but symptoms commonly resolve without treatment
• may also be complicated by either reactive arthritis or Guillain-Barre syndrome with an ascending paralysis

Question 41

Yersinia enterocolitica

Answer 41

• an encapsulated, gram-negative bacillus that survives cold temperatures well
• known for its bipolar, “safety pin” staining
• found in puppy feces and contaminated dairy products
• causes a bloody diarrhea and may present with right lower quadrant pain, mimicking appendicitis
• diagnosis is based on culture of stool or mesenteric lymph node
• treated with third-generation cephalosporins

Question 42

Clostridium difficile

Answer 42

• an obligate anaerobe, spore-forming, gram positive rod
• often seen as a nosocomial infection in those who have been taking clindamycin or ampicillin
• spread by healthcare workers who don’t wash their hands well
• exotoxin A, aka enterotoxin, targets the brush border, damages the mucosal lining of the colon, and causes watery diarrhea
• exotoxin B, aka cytotoxin, causes actin depolymerization, necrosis of colonic mucosal surfaces, and the formation of pseudomembranes
• diagnosis is made using a PCR TOXIN ASSAY of the stool
• treat with oral vancomycin or metronidazole

Question 43

Vibrio cholerae

Answer 43

• an acid-labile, oxidase-positive, “comma-shaped” gram-negative bacillus
• spread via the fecal-oral route and is endemic to South American countries with poor sanitation
• it uses fibrae to attach the the wall of the intestine but does not invade; instead, it secretes cholera toxin, which constitutively activates AC and increases cAMP levels
• causes a watery diarrhea described as “rice water stool” with massive water loss
• diagnosed in the US via serology
• treat with fluid replacement

Question 44

Diarrhea causes what sort of electrolyte imbalance?

Answer 44

a non-angio gap hyperchloremic metabolic acidosis due to bicarbonate loss

Question 45

HIV

Answer 45

• a virus acquired in utero, intrapartum, or postpartum via breastfeeding, via sexual contact, or parenterally
• risk of transmission is increased by a high maternal viral lode, primary maternal infection, concomitant maternal genital infections, premature birth and prolonged rupture of membranes; decreased by c-section, maternal antiretroviral therapy, and post-exposure prophylaxis with 6 weeks of zidovudine as well as avoidance of breastfeeding
• usually asymptomatic in the first year of life but may exhibit failure to thrive, thrombocytopenia, recurrent infections, lymphadenopathy, parotitis, thrush, loss of developmental milestones, and severe varicella
• infants born to HIV-postivie mothers will have maternal antibody that persists for 18-24 months; monitor this as well as HIV-specific DNA via PCR
• PCR is performed monthly, and if negative at 4 months, is indicative of an uninfected child; continue to follow antibody levels until 18-24 months or absent
• may be complicated by PCP infection (fever, hypoxia, and interstitial pulmonary infiltrates), M. avium complex, fungal infection, viral infection, toxoplasmosis, or cryptosporidium
• in high-risk individuals, use TMP/SMX for PCP prophylaxis until 4 months of age and perform urine CMV culture to detect connection
• antiretroviral therapy should be used once infection has been confirmed and continue prophylaxis for PCP and CMV
• infected individuals should get all routine childhood vaccines except the live varicella vaccine (live MMR is still recommended), annual influenza, pneumococcal vaccine, and annual TB skin testing; they also need monitoring of T-cells and viral load and annual ophthalmologic examination to assess for CMV retinitis

Question 46

Infectious Mono

Answer 46

• a lymphocytic leukocytosis comprised of CD8 T cells
• most commonly due to EBV with CMV infection less common
• primarily infects the oropharynx, liver, and B cells causing pharyngitis and hepatitis
• presents as fever, fatigue, exudative pharyngitis, posterior cervical lymphadenopathy, hepatosplenomegly, and macular or scarlatiniform rash
• CD8 response leads to generalized lymphadenopathy due to hyperplasia in the paracortex and splenomegaly due to hyperplasia in the periarterial lymphatic sheath
• increased risk of splenic rupture, ampicillin rash, and B-cell lymphoma
• screen using the mono spot test, which detects IgM antibodies that cross-react with horse or sheep RBCs (called heterophiles antibodies) one week after infection
• a negative monospot test suggests CMV rather than EBV
• monospot testing is less sensitive in children under the age of four and these individuals should be tested with eBV antibody titers: should see elevated levels of viral capsid antigen-IgM and absent Epstein Barr nuclear antigen antibodies because these appear 2-3 months after infection
• definitively diagnosed based on serologic testing for the EBV viral capsid

Question 47

Pneumocystis carinii pneumonia

Answer 47

• the most common opportunistic infection in HIV-infected children
• presents with fever, hypoxia, and interstitial pulmonary infiltrates
• use TMP/SMX as prophylaxis in at risk individuals

Question 48

What is an amoxicillin-associated rash?

Answer 48

a diffuse pruritic maculopapular rash seen 1 week after starting the antibiotic, which is an idiosyncratic reaction in those with infectious mono and is not an allergic reaction

Question 49

Measles

Answer 49

• an RNA virus of the paramyxoviridae family
• presents with a prodrome of the three C’s: cough, conjunctivitis, and coryza; there may also be photophobia and low-grade fever
• this is followed by an enanthem with Koplik spots, small gray papules on an erythematous base which are transient and may be absent by the time the patient presents
• an erythematous maculopapular eruption is seen next, beginning around the neck and ears before spreading to the chest and upper extremities; if affects the lower extremities by day 2, is confluent on day 3, and lasts 4-7 days
• treat with supportive care and vitamin A
• may be complicated by bacterial pneumonia, otitis media, laryngotracheitis, encephalomyelitis, or subacute sclerosing panencephalitis years later

Question 50

Rubella

Answer 50

• an RNA virus of the togavirus family
• shorter and milder than measles
• presents with a prodrome of URI symptoms and low-grade fever, followed by painful lymphadenopathy of the sub occipital, posterior auricular, and cervical nodes
• a non-pruritic, maculopapular, and confluent exanthem follows, beginning on the face and spreading to the trunk, lasting a total of 3-4 days
• diagnosed with viral culture and serology
• treatment is supportive
• may be complicated by meningoencephalitis, polyarteritis, or congenital rubella syndome (congenital cataracts, sensorineural hearing loss, and PDA)

Question 51

What is congenital rubella syndrome?

Answer 51

• the most serious complication of rubella
• occurs following primary maternal infection during the first trimester
• presents with thrombocytopenia, hepatosplenomegaly, jaundice, and purpura
• the major complications, however, are PDA, congenital cataracts, and sensorineural hearing loss