Infectious Diseases

Question 1

What is malaria? How is it transmitted?

Answer 1

Malaria is a protozoan disease transmitted by the female anopheles mosquito. Most common forms are falciparum and vivax.

Question 2

What are the symptoms of malaria infection? What is the time course?

Answer 2

Symptoms start 12-14 days after exposure.

Mild/moderate symptoms are usually nonspecific: malaise, fatigue, headache, myalgia, abdominal discomfort, followed by irregular fever, often with nausea, vomiting, orthostatic hypotension.

Question 3

How is malaria treated?

Answer 3

If the patient contracted malaria in a chloroquine sensitive area chloroquine and hydroxychloroquine can be used.

If malaria is resistant or unknown can use artemisinin or atovaquone-proguanil.

Question 4

What is Babesia?

Answer 4

Babesia is a tick borne illness caused by protozoan infections. It infects erythrocytes causing lyses.

Question 5

What is the epidemiology of Babesia?

Answer 5

• Primarily endemic to northeastern coastal United States
  
  • Babesia microti transmitted by Ixodes scapularis tick
  • Prevalence between 3.7-6.9%
• Disease severity ranges between asymptomatic infection to fulminant course
  
  • Symptoms generally develop 1-6 weeks following tick bite

Question 6

How do you diagnose Babesia?

Answer 6

• Microscopy (manual review of thin blood smear)
  
  • “Maltese Cross”
  • Ring forms
• Serum Babesia PCR
  
  • Particularly useful in low-level parasitemia
• Babesia serology (IgM and IgG)
  
  • Not alone sufficient for diagnosis
  • Infectious symptoms precede rise in antibodies
• Should check other serologies
  
  • Anaplasma and Lyme

Question 7

What is the treatment for Babesiosis?

Answer 7

• Antibiotics
  
  • Standard course: 7-10 days
  • Atovaquone + azithromycin for mild/moderate disease
  • Clindamycin + quinine for severe disease*
• Blood transfusions
• Exchange transfusions; Indicated for severe anemia Hgb < 10 and high grade parasitemia (>10%) OR High grade parasitemia and immediate risk of organ collapse. Goal is to remove infected RBC and clear inflammatory mediators/toxins

Question 8

What is a lung abscess?

Answer 8

• A localized area of necrosis of the lung parenchyma caused by pyogenic organisms
  
  • Also known as: “necrotizing pneumonia” or “lung gangrene”
• On CXR or CT scan, shows up as cavity with air-fluid level

Question 9

What is the etiology of a lung abscess?

Answer 9

• Most commonly a sequelae of aspiration pneumonia. Pneumonitis arises first and progresses to tissue necrosis after 7 to 14 days
• Aspiration
  
  • Depressed consciousness (alcoholism, drug abuse, general anesthesia, head trauma)
  • Impaired laryngeal closure
  • Dysphagia
  • Delayed gastric emptying/multiple episodes of vomiting
• Dental/periodontal infection
• Septic emboli
• Trauma
• Infected pulmonary infarct

Question 10

How is a lung abscess diagnosed?

Answer 10

• Sputum culture obtained prior to antibiotics
  
  • If only aerobic bacteria, still need to cover anaerobic bacteria
• Blood cultures
  
  • Rarely positive if caused by anaerobe
• Imaging:
  
  • CT scan if there is a question of cavitation that cannot be clearly delineated on CXR or if an associated mass lesion is suspected

Question 11

How do you treat a lung abscess?

Answer 11

• Empiric treatment with Unasyn or carbepenem (can use Clindamycin)
  
  • Do NOT use flagyl as monotherapy (failed 50% of time)
  • Daptomycin is inactivated by surfactant
• Treatment duration depends: at least 3 weeks of IV antibiotics
• Surgery; when medical management fails, suspected malignancy, hemorrhage

Question 12

What is Anaplasma?

Answer 12

Obligate intracellular bacteria that grows within membrane bound vacuoles in human and animal leukocytes.

Vector is Ixodes Scapularis (similar vector as lyme disease and babesiosis).

Coinfetion with Lyme occurs in 3-15% of the cases.

Question 13

What are the symptoms of anaplasma? What are the lab abnormalities?

Answer 13

Incubation period of about 1 week (5.5 days)

Common (66%): Fever, malaise, myalgia, headache

Less common (25-50%): nausea, abdominal pain, diarrhea, cough

Rash rare in anaplasma, so think of co-infection with Lyme or Rickesttsia if you see a rash.

Lab abnormalitites: Thrombocytopenia, elevated transaminases, leukopenia with left shift, anemia.

Question 14

How do you diagnose anaplasma?

Answer 14

Indirect fluorescent antibody (IFA) test

–Sensitivity 94-100%, but can take 2-3 weeks to turn positive

Peripheral blood smear for intraleukocytic morulae

PCR for HGA

–sensitivity 60-70%

Question 15

What is the treatment for Anaplasma?

Answer 15

Treat with doxycycline for 10 days, this will also treat co-infection with boreilla.

If allergic to doxycycline can treat with rifampin.

Question 16

What is cryptococcus? What is its reservoir? What is the transmission? What are risk factors?

Answer 16

Cryptococcus is a type of opportunistic, encapsulated yeast that most commonly affects immunosuppressed individuals.

The reservoir is pigeons, chickens, and eucalyptus trees.

Transmission is via respiraory particles.

Vast majority of cases occur among patients with AIDS (CD4 count < 100). Other at risk groups are HIV/AIDS, glucocorticoid therapy, solid organ transplant, hematologic malignancies, sarcoidosis, hepatic failure.

Question 17

How does cryptococcus present? How do you make the diagnosis?

Answer 17

Subacute presentation occuring over one to two weeks. Fever, malaise, and headache with stiff neck, photophobia, and nausea/vomiting.

Diagnosis is made via LP (CT scan prior), opening pressure is greater than 25, cell coun is 20-200 with lymphocytic/mononuclear cells predominant, low glucose and elevated protein.

Can use india ink staining of CSF, CSF crypto antigen is very sensitive and specific, serum crypto antigen can help determine disease burden.

Question 18

How do you treat cryptococcus?

Answer 18

Amphoteicin B with Flucytosine. Repeat LP at 2 weeks if CSF cultures are negative can start on Fluconazole.

Need to manage increased ICP with therapeutic lumbar punctures.

Question 19

What is prophylaxis and treatment for PCP in HIV patients?

Answer 19

PCP prophylaxis should be initiated with CD4 less than 200 with Bactrim DS tablet daily.

Treatment; Bactrim (dose depending on severity) with corticosteroids if PaO2 < 70 or A-a O2 gradient > 35.

Question 20

How do you provide prophylaxis for Toxoplasma gondii in HIV patiens? How do you treat?

Answer 20

Provide prophylaxis with a CD4 count lesss than 100 in IgG positive patient with Bactrim DS tablet once daily.

Treat with pyrimethamine 200 mg daily.

Question 21

How you provide prophylaxis for mycobacterium avium in HIV patients? How do you treat?

Answer 21

Prophylaxis once CD4 count is less than 50 with Azithromycin 1200 mg once weekly or clarithromycin 500 mg BID until CD4 count is > 100 for three months.

Treat with Clarithromycin 500 mg oral BID with ethambutol until CD4 > 100 for 6 months and no more symptoms.

Question 22

What is hemolytic uremic syndrome?

Answer 22

• Predominantly a pediatric disease with morbidity ranging between 5-10%.
  
  • Up to 30% will have residual renal deficits.
• Associated with e. Coli O157:H7 (shiga like toxin), Shigella, and campylobacter

Question 23

How does HUS present?

Answer 23

• Presents with diarrhea -> bloody diarrhea and hemorrhagic colitis
• 5-10 days after diarrhea:
  
  • Oliguria
  • Hematuria
  • Thrombocytopenia/anemia
  • +/- HTN, neuro changes

Question 24

How do you differentiate HUS from TTP?

Answer 24

• HUS and TTP both present with acute renal failure, microangiopathic hemolytic anemia, and thrombocytopenia.
• However; TTP presentes with fever, altered mental status, and a prodrome of purpuric skin lesions (as opossed to diarrheal prodrome).
  
  • In TTP ADAMTS13 is absent while in HUS it is reduced.

Question 25

How do you treat HUS?

Answer 25

• Treat with plasma exchange.
• Eculizumab (Soliris); C5a-inhibiotr