Other Choices

Streptococci A or B




Penicillin + aminoglycoside

Vancomycin + aminoglycoside




Haemophilus sp.

Second- or third -generation cephalosporin


Bocteruiita sp.



Ticpononu sp.



Escherichia colt

.Third-generation cephalosporin


Rickettsia sp.



Mycobacterium-Tuberculosis . -..


lithambutof pyrazinamide

Streptococcus pneumoniae


Erythromycin, third-generation cephalosporin


Antisiaphylococcä! penidllm

Vancomycin (MRSA)


Penicillin / Ampicillin

Cefotaxime, chloramphenicol

Pseudomonas sp.

Penicillin + aminoglycoside

Arfreonam, imipertem

Mycoplasma sp.



CMoroydiü sp.



Boi rcliü sp,



Klebsiella sp.

Third-generation cephalosporin

Third-generation penicillin -i- aminoglycoside..

MRSA ~ methicillin-resistant S. <wrens.

MRSA ~ methicillin-resistant S. <wrens.

■ Gram-negative diplococci = Neisseria (gonorrhea, septic arthritis, meningitis) or Momxella sp. (lungs, sinusitis)

m Gram-negative rod that is plump and has thick capsule (mucoid appearance) = Klebsiella sp.

■ Gram-positive rods that form spores = Clostridium, Bacillus spp.

a Acid-fast organisms = Mycobacterium tuberculosis, Noamlia sp.

a Gram-positive oragnism with sulfur granules — Actinomyces sp. (pelvic inflammatory disease in women who use intrauterine devices; rare cause of neck mass/cervical adenitis)

■ Silver-staining — Pneumocystis airinii (PCP) and cat-scratch disease

* Positive India ink preparation (thick capsule) — Cryptococais sp.

« Spirochete = Treponema, Leptospira spp. (both seen only on dark-field microscopy), Borrdiu sp. (regular light microscope)

Pneumonia: look for classic clues to differentiate. The gold standard for diagnosis is sputum culture; do blood cultures, too;

1. Streptococcus pneumoniae: most common cause, especially in older adults. Look for rapid onset of shaking chills alter an upper respiratory infection, then lever, pleurisy, and productive cough (yellowish-green or rust-colored from blood). X-ray shows lobar consolidation. White blood cell count is high, with large percentage of neutrophils. Give vaccine to patients older than 65 yr, splenei tomized patients, patients with sickle cell disease, im munocompromised patients (HIV, malignancy, organ transplant), and all patients with chronic disease (diabetes mellitus, cardiac, pulmonary, renal, or liver disease). For board questions, penicillin is still the empiric drug of choice.

2. Haemophilus influenzae: second only to S. pneumoniae as most common cause of pneumo nia; more common in young children. Resembles S. pneumoniae clinically. Treat with ampicillin/ amoxicillin, cephalosporin, or trimethoprim/sulfamethoxazole if gram-negative coccobacilli are seen on sputum Gram stain.

3. Staphylococcus aureus: causes hospital-acquired pneumonia and pneumonia in patients with cystic fibrosis (second to Psetrdoinonas sp.), intravenous drug abusers, and patients with chronic granulomatous disease (look for recurrent lung abscesses). Empyema and lung abscesses are relatively common. Cultures usually are positive.

4, Gram-negative organisms: Pseudomoiws sp. classically is associated with cystic, fibrosis; Klebsiella sp. i.s classic cause in skid-row alcoholics and homeless people; enteric gram-negative organisms (e.g., E. coli) are common with aspiration, neutropenia and hospital-acquired pneumonia. High mortality rate because of patients affected and severity of pneumonia (abscesses common). Treat empirically with third-generation penicillin/cephalosporin plus aminoglycoside.

5- Mycoplasma sp: most common in adolescents and young adults (the classic case is a college student who lives in the dorm and has sick contacts). Called "atypical" penumonia because it is different from S. pneumoniae, with long prodrome and gradual worsening of malaise, headaches, dry nonproductive cough, and sore throat. Chest x-ray shows a patchy, dill use bronchopneumonia (the x-ray classically looks terrible, although the patient does not feel that bad). look for positive cold-agglutinin antibody titers (may cause hemolysis/anernia). Empiric treatment of "atypical" pneumonia is erythromycin.

6. Chlamydia pneumoniae: second only to Mycoplasma sp. as cause of pneumonia in adolescents and young adults; presents similarly but has negative coid-agglutinin antibody titers.

7. Viral pneumonia: viruses commonly cause respiratory infections (respiratory syncytial virus, influenza, parainfluenza, adenovirus)

8. Pneumocystis eunnii pneumonia (PCP) and cytomegalovirus (CMV): always suspect in HIVpositive patients. PCP is more common; bronchoalveolar lavage often is required to obtain the diagnosis. PCP shows up with, silver stains—know what it looks like. Treat with trimethoprim/sulfamethoxazole; the alternative is pentamidine. PCP is acquired when the CD4 count is below 200, at which point you should institute PCP prophylaxis in. an HIV-positive patient. CMV has intracellular inclusion bodies. Treat with ganciclovir; fos-carnet is an alternative.

Classic infectious disease questions:

■ Patient stuck with thorn or gardener: Sporothm schenckii (a fungus).Treat with oral potassium iodide or ketoconazole.

s Aplastic crisis in sickle cell disease or other hemoglobinopathy: parvovirus B19

■ Sepsis after splenectomy (or autosplenectomy in sickle cell disease): S. pneumoniae, H. infiucn-

■m, N. meningitidis (encapsulated bugs)

■ Pneumonia in the Southwest (California, Arizona): Coccidioides immilis. Treat with amphotericin B.

■ Pneumonia after cave exploring or exposure to bird droppings in Ohio and Mississippi

Rivet" valleys: Bistopittsmu capsulatuni

■ Pneumonia after exposure, to a parrot or exotic bird: Chlamydia psiltaa

■ Fungus ball/hemoptysis after tubercular cavitary disease: Aspergillus sp.

■ Pneumonia in a patient with silicosis: tuberculosis

■ Diarrhea after hiking or drinking from a stream: G'iordia lambiia; cysts in stool; treat with metronidazole a Pregnant women with cats: Toxoplasma gondii » Bri deficiency and abdominal symptoms: Diphyllobolhrtum latum

■ Seizures with ring-enhancing brain lesion on CT: Taenia solium (cystjcercosis)

E3 Bladder cancer (squamous cell) in Middle East and Africa: Schistosoma haematobium

■ Worm infection in children: Enicrobius sp. (positive tape test, perianal itching)

■ Fever, muscle pain, eosinophilia, and periorbital edema after eating raw meat: Trichindla spiralis (trichinosis)

a Gastroenteritis in young children: rotavirus

■ Food poisoning after eating reheated rice: Bacillus cereus s Food poisoning after eating raw seafood: Vibrio purahaemolytieus

■ Diarrhea after traveling to Mexico: Escherichia coli (Montezuma's revenge)

■ Diarrhea after antibiotics: Clostridium difficile; treat with metronidazole or vancomycin

■ Infant paralyzed after eating honey: Clostridium botulinum (toxin blocks acetylcholine release)

■ Genital lesions in children in the absence of sexual abuse/activity: moiluscum coutagiosum

■ Cellulitis after cat or dog bites: Pasteurella multocida (treat cat and dog bites with prophylactic ampicillin)

■ Slaughterhouse worker with fever: Brucella sp.

■ Pneumonia after being in. a hotel, near air conditioner or water tower: Legionella pneumophila; treat with erythromycin)

■ Burn wound infection with bine/green color: Pseudomoiws sp. (S. aureus also common, but without blue-green color)

Syphilis: screen with Venereal Disease Research Laboratory (VDRL) or rapid plasma reagin (RPR) test; if positive, confirm with fluorescent treponemal antibody, absorbed (FTA-ABS) or microhemagglutination Treponema pallidum (MHA-TP) test, Treponema pallidum also can be seen with darkfield microscopy but not with a Gram stain. Screen all pregnant women with VDRL/RPR. Treatment is penicillin; use erythromycin for penicillin allergy. Three stages:

1. Primary: look for painless chancre that resolves on its own within 8 weeks.

2. Secondary: roughly 6 weeks to 18 months after infection; look for condyloma lata, mjcu-lopapular rash (especially involving palms and soles of feet), and lymphadeiiopathy.

3. Tertiary: occurs years after initial infection; between secondary and tertiary stages is the latent phase, when the disease is quiet and asymptomatic. Look for gummas (granulomas in many different organs), neurologic symptoms and signs (neurosyphilis, Argyll-Robertson pupil, dementia, paresis, tabes dorsalis, Charcot joints), and/or thoracic aortic aneurysms.

Note: Watch for false-positive VDRL/RPR in patients with lupus erythematosus. For other sexually transmitted diseases, see gynecology section.

Infections rashes (most often in children; supportive treatment only unless otherwise specified) .1. Measles (rubeola): look for a reason for patient not to be immunized. Koplik's spots (tiny white spots on buccal mucosa) are seen 3 days after high fever. Other symptoms include cough., runny nose, and conjunctivitis/photophobia. On the next day, the rash (maculopapular) begins on. the head and neck and spreads downward to cover the trunk (cepbaloeaudal progression). Complications include pneumonia (giant-cell pneumonia.

especially in very young and iminunoconipromised patients), otitis media, and encephalitis (which may be acute or cause subacute sclerosing panencephalitis [SSPE], which usually occurs years later).

2. Rubella (German measles): most important because of infection in pregnant women. Screen and immunize any woman of reproductive age before she becomes pregnant; the vaccine contramdieated in pregnant women. Rubella is milder than measles with low fever, malaise, tender swelling of the suboccipital and postaurieular nodes, and arlhral gias. After a Z -3-day prodrome, the rash (maculopapular, faint) starts on the face and neck and spreads to the trunk (cephaJoea tidal progression). Complications include en cephalitis and otitis media.

3. Roseola infantum (exanthein subitum): easy to recognize because of progression: high fever (may be > 40° C) with no apparent cause for 4 days (patient may get febrile seizures), then an abrupt return to normal temperature as a diffuse macular/inacu-lopapular rash appears on the chest and abdomen. Rare in children older than 3 years, it is caused by the human herpesvirus type 6 (a DMA virus).

4. Erythema infect iosum (fifth disease): classic "slapped-cheek" rash (confluent erythema over the cheeks) appears around the same time as mild constitutional symptoms (low fever, malaise). One day later, a maculopapular rash appears on the arms, legs, and trunk. It is caused by parvovirus BI9 (the same virus that causes aplastic crisis in sickle cell disease).

5. Chickenpox (varicella): the description and progression of the rash itself shou ld lead to the diagnosis: discrete macules (usually on the trunk) turn into papules, which turn into vesicles that rupture and crust over. These changes occur within I day. The lesions appear in successive crops; therefore, the rash is in different stages of progression in different areas. The patient is infectious until the last lesion crusts over. A complication is infection of the lesions (streptococci, staphylococci—erysipelas, cellulitis, sepsis). The patient should be instructed to keep clean to avoid infection. Other complications include pneumonia (especially in very young children and immunocompromised adults), encephalitis, and Reye's syndrome. Do not give aspirin to any child with a fever unless the diagnosis requires its use. A Tzanck smear of tissue from the base of a vesicle shows multinucleated giant cells. Varicella zoster immunoglobulin (VZIG) is available lor prophylaxis in patients with debilitating illness (e.g., leukemia, AIDS) if you see them with in 4 days of exposure or in newborns of mothers with chicken pox. Acyclovir may be used in severe cases.The varicella zoster virus can reactivate years later to cause shingles (zoster), which is characterized by dermatomal distribution of rash. Pain and paresthesias often precede the rash.

6. Scarlet fever: look for a history of untreated streptococcal pharyngi tis (caused only by .Streptococcus species that produce erythrogenic toxin), followed by a sandpaper-like rash on the abdomen and trunk with classic c ¡immoral pallor and strawberry tongue. The rash tends to desquamate once the fever subsides. Treat with penicillin to prevent rheumatic fever.

1, Kawasaki's syndrome (mucocutaneous lymph node syndrome): rare; usually occurs in patients younger than 5 years. Diagnostic: criteria include fever > 5 days (mandatory for diagnosis); bilateral conjunctival injection; changes in the lips, tongue, or oral mucosa (strawberry tongue, fissurmg, injection); changes in the extremities (desquamation, edema, erythema); polymorphous truncal rash (usually begins one day after the fever starts); and cervical lymphadenopatby. Also look for arthralgia or arthritis.The most feared complications involve the heart (coronary artery aneurysms, congestive heart fail ure, arrhythmias, myocarditis, myocardial infarction). Think of Kawasaki's syndrome in the differential diagnosis of any child who has a myocardial infarction. If suspicion is high, give aspirin and IV immunoglobulin, both of which reduce cardiac lesions, follow-up with cdKJcaiTfiography to detect heart involvement.

8. Infections mononucleosis (Epstein Barr virus [EBV] infection): look for fatigue, fever, pharyngitis, and lymph adenopathy (.similar to streptococcal pharyngitis, but malaise tends to be more prolonged and pronounced).To differentiate from streptococcal disease, look for splenomegaly; hepatomegaly; atypical lymphocytes (bizarre forms that may resemble leukemia) with lymphocytosis, anemia, or thrombocytopenia; and positive serology (heterophile antibodies [e.g., monospot test] or specific EBV antibodies: VCA, EBNA). Patients may develop splenic rupture and should avoid contact sports and heavy lifting. Include 111V in the differential diagnosis. Remember the association of EBV with nasopharyngeal cancer and African Burkitt's lymphoma.

3. Rocky Mountain spotted fever (Rickettsia ric.ket.tsii infection): look for history of a tick bite (especially on the East Coast) one week before the development of high fever or chills, severe headache, and prostration or .severe malaise. The rash appears roughly 4 days after symptoms on the palms/wrists and soles/ankles, rapidly spreading to the trunk and face (unique pattern of spread). Patients look very sick (disseminated intravascular coagulation, delirium) and require tetracycline and chloramphenicol immediately.

10. Impetigo: look lor history of skin break (e.g., previous chickenpox, inset:! bite, scabies, cut).The rash starts as thin- walled vesicles that rupture and form yellowish crusts.The skin often is described as "weeping." Classically, lesions are on the face and tend to be localized. impetigo is infectious; look for sick contacts. Treat with oral antistaphylococcal penicillin to cover streptococci and staphylococci, the most common causative bugs.

Endocarditis: either acute (fulminant, most commonly caused by S. aureus) or subacute (insidious onset, most commonly caused by Streptococcus viriikms). 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), Roth spots (round reti nal hemorrhages with white centers), and septic shock (more dramatic with acute than subacute disease). Diagnosis is made by blood cultures. Empiric treatment is begun with wide spectrum antibiotics until culture and sensitivity results are known. A third- generation penicillin or cephalosporin plus aminoglycoside is a reasonable choice. Patients more likely to be affected include IV drug abusers (who develop right sided lesions, although left sided lesions are much more common in the general population), patients with abnormal heart valves (prosthetic valves, rheumatic valvular disease, congenital heart defects, such as ventricular septal defect; or tetralogy of Fallot), and postoperative patients (especially after genitourinary, gastrointestinal, or denial surgery). Hence the need for prophylaxis in susceptible people. Any patient with known valvular disease is given oral amoxicillin (erythromycin if the patient is penicillin allergic) before and after dental procedures (to cover S. vrridans) and IV ampiciliin (vancomycin if the patien t is penicillin allergic) before and amoxicillin/gentamicin before and. after gastrointestinal or genitourinary procedures (to cover enterococci). Patients with secundum atrial septal defect (the more common type) as well as patients with mitral valve prolapse and no audible murmur are not given endocarditis prophylaxis.

Meningitis: t he highest incidence of meningitis is seen in neonates; > 75% of cases are seen in patients younger than 2 years.Thus tire decision about when to do a lumbar tap is difficult, be cause such patients often do not have classic physical findings (Kernig's and Brudzinski's signs). Look for lethargy, hyper- or hypothermia, poor tone, bulging fontanelle, vomiting, photophobia, altered consciousness, and signs of generalized sepsis (hypotension, jaundice, respiratory distress). Seizures may be seen, but simple febrile seizures also are possible if the patient is between 5 months and 6 years old and has a fever > 102° t in the absence of other signs of meningi tis. If seizures occur in the presence of other signs of meningi tis or sepsis, proceed to lumbar puncture immediately and begin broad-spectrum antibiotics immediately after the procedure. The most common neurologic sequela of meningitis is hearing loss. All patients need formal hearing evaluation after a bout of meningiLis; vision testing also is recommended. Other sequelae include mental retardation, motor deficits/paresis, epilepsy, and learning/behavioral disorders.

■ Murnps and measles are possible causes of aseptic (nonbacterial or culture-negative) meningitis. Hie best prevention is immunization.

■ Watch for herpes encephalitis ift.be mother has herpes simplex lesions at the time of the infant's birth. Look for temporal lobe abnormalities on a CT or MR I scan of the head. Give acyclovir.

■ If meningitis is due to Neisseria sp., give all contacts rifampin as prophylaxis.

« For cerebrospinal fluid findings in meningitis, see the neurology chapter.

Pediatric respiratory infections: the big three are croup, epiglottitis, and respiratory syncytial virus (RSV)—high yield!

1. Croup/acute laryngotracheitis: look for patient to be .1-2 years old; usually occurs in fall or winter. About 50-75% of cases are due to parainfluenza virus; the other causative agent is influenza. Patients start with symptoms of viral upper respiratory infection (rhinorrhea, cough, and fever) and roughly 1-2 days later develop a "barking" cough, hoarseness, and inspiratory stridor. The "steeple sign" is classic on lateral x-ray of die neck. Treat support-ively with a mist tent and racemic epinephrine.

2. Epiglottitis: the patient usually is 2-5 years old. The main cause by far used to be Haemophilus influenzae type b, but with widespread vaccination, H, influenzae and. S, aureus are equally frequent. Pick H. influenzae if you have to choose. Look for little or no prodrome, with rapid progression to high fever, toxic appearance, drooling, and respiratory distress with no coughing. The "thumb sign" is classic on lateral neck x-ray. Do not examine the throat or irritate the patient in any way—you may precipitate airway obstruction. When a case of epiglottitis is presented, the first step is to be prepared to establish an airway (intubate, tracheostomy if needed). Treat with antibiotics (e.g., third-generation cephalosporin).

3. RSV/bronchiolitis: look for 0-18 months old patient; usually occurs in fall or winter. Over 75% of cases are caused by RSV; other causes are parainfluenza and influenza. Patients start with symptoms of viral upper respiratory infection, followed 1—2 days later by rapid respirations, intercostal retractions, and expiratory wheezing. The patient also may have crackles on auscultation of the chest. Diffuse hyperinflation of the lungs is classic on chest x-ray; look for flattened diaphragms.Treat supportively (oxygen, mist tent, bronchodilators, IV fluids). Use ribavarin in patients with severe symptoms or increased risk (cyanosis, other health problems).

Note: Diphtheria (Corynebacterium diphtheriac) and pertussis (BordeteHa pertussis) should be considered if the patient is not immunized. Diphtheria is associated with grayish psendomembranes (necrotic epithelium and inflammatory exudate) on the pharynx, tonsils, and/or uvula and myocarditis. Pertussis is associated with severe paroxysmal coughing and. a high-pitched whooping inspiratory noise (classically called "whooping cough").Treat both with antibiotics.

Rabies: in the U.S., usually due to bites from bats, skunks, raccoons, or foxes. Vaccination has eliminated dog rabies. The incubation period is usually around 1 2 months. Classic symptoms are hydrophobia and central nervous system signs (paralysis). After a bite, several steps should be taken:

1. Local wound treatment: cleanse thoroughly with soap; do not cauterize or suture the wound.

2. Observe the animal. If possible, capture and observe a dog or cat to see if it develops rabies. If a wild animal (bat, skunk, raccoon, fox) is caught, it should be killed and the tissue examined for rabies.

3. Prophylaxis with rabies immunoglobulin and vaccine:

h if a captured or killed animal has rabies, definitely give prophylaxis and vaccinate.

m if a wild animal (bat, skunk, raccoon, fox only) bites and escapes, give prophylaxis and vaccine.

¡n If a dog or cat bites and escapes, do not give prophylaxis or vaccine unless the animal acted strangely and/or bit the patienht without provocation titid rabies is prevalent in the area (rare).

a Do not give prophylaxis or vaccine for bites by rabbits or other rodents (rats, mice, squirrels, chipmunks).

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