MCQs In Pediatric Infectious Diseases

Q 1 :

An 8-year-old girl presents with a 4-day history of fever, headache, and abdominal pain. Her mother states that they live in a rural area and have multiple pets, including dogs, cats, horses,cows, and a pet raccoon. There is no history of tick bites. On physical examination, the girl appears mildly toxic, has a temperature of 102.2°F (39°C), and has a grade II/VI systolic ejection murmur best heard on the left side of the sternal border. Her right upper quadrant is tender to palpation, but there is no hepatosplenomegaly. Findings on her skin and extremity examination are normal. A complete blood count reveals a white blood cell count of 1.2x103/mcL (1.2x109/L) with 90% neutrophils and 10% lymphocytes. Her hemoglobin is 10 g/dL (100 g/L), and her platelet count is 50x103/mcL (50x109/L). Her alanine aminotransferase is 600 U/L, and her

aspartate aminotransferase is 450 U/L. Her amylase and lipase values are normal. Serum sodium is 133 mEq/L (133 mmol/L), but the remainder of her electrolyte values are normal.

Of the following, the MOST likely diagnosis is

A. human monocytic ehrlichiosis

B. Lyme disease

C. Rocky Mountain spotted fever

D. tularemia

E. typhus

Answer :

A


Explanation


Human monocytic ehrlichiosis (HME) is a rickettsial disease caused by Ehrlichia chaffeensis,which is transmitted to humans by the bite of a tick. 

Clinically, the ehrlichioses are nonspecific illnesses. Fever (~100%) and headache (~75%) are most common, but many patients also report myalgias, anorexia, nausea, and vomiting.

With HME, rash is more common in children (nearly 66%) than in adults (33%). The rash is usually macular or maculopapular, but petechial lesions can occur.

Photophobia, conjunctivitis, pharyngitis, arthralgias, and lymphadenopathy are less consistent features.

  Hepatomegaly and splenomegaly are detected in nearly 50% of children with ehrlichiosis.

Edema of the face, hands, and feet occurs more commonly in children than in adults, but arthritis is uncommon in both groups.


 A rash is described in approximately two thirds of children and one third of adults and starts as maculopapular but may progress into petechial/purpuric.

Meningoencephalitis with a lymphocyte-predominant CSF pleocytosis is an uncommon but potentially severe complication of HME

HME is clinically indistinguishable from Rocky Mountain spotted fever (RMSF).

Laboratory abnormalities common to both infections include thrombocytopenia and hyponatremia, but
patients who have HME are more likely to have elevated liver function test results and
leukopenia with lymphopenia. Approximately 50% to 75% of patients have no history of a tick
bite.


Patients who have Lyme disease typically do not appear toxic or have the laboratory abnormalities described in the vignette.

 Although there is a typhoidal form of illness due to Francisella tularensis (tularemia), it is extremely rare, and most affected children present with glandular or ulceroglandular disease. Typhus can be endemic or epidemic.

 Epidemic typhus is due to the bite of the human louse, and endemic typhus is caused by a mite bite. Although both of these rickettsial diseases can present with fever and a headache, patients usually are not
toxic and do not have laboratory abnormalities such as those reported for the girl in the vignette.

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Q2 :


A 4-year-old boy presents to your office for evaluation of a 3-day history of fever (temperature to 38.5°C), congestion, and sore throat. Physical examination of the well-appearing child shows only rhinorrhea and pharyngeal erythema. His mother and 6-year-old sister have had colds over the past week.
Of the following, the MOST appropriate treatment for this child, pending the results of the throat culture, is

A. amoxicillin
B. azithromycin
C. nasal saline drops
D. prednisone
E. pseudoephedrine

Answer :

C


The congestion and sore throat described for the boy in the vignette, combined with the history of upper respiratory tract infections in the family, strongly suggest that he has a viral illness. Supportive therapy such as nasal saline drops to relieve congestion is appropriate.

Cough and cold remedies, including those containing the decongestant pseudoephedrine, have not been demonstrated to be effective in treating viral upper respiratory tract infection symptoms, and based on potential toxicities in young children, the American Academy of Pediatrics and United States Food and Drug Administration have advised against their use in children younger than 6 years of age.

 There is no indication for prednisone in this setting. However, high-dose, short-term corticosteroid therapy may be beneficial in the treatment of the patient who has marked pharyngitis and impending airway obstruction associated with acute infectious mononucleosis.

Antibiotics are not indicated to treat a viral illness and do not prevent development of possible secondary bacterial infections (eg, otitis media, sinusitis).

 Increased use of antibiotics has been associated with increased rates of carriage of resistant bacteria (eg, penicillin-resistant Streptococcus pneumoniae, beta-lactamase-positive Haemophilus influenzae, methicillin-resistant Staphylococcus aureus).

Other common illnesses that generally do not require antibiotic therapy in children include bronchitis, middle ear effusion of short duration, mucopurulent rhinitis of less than 10 days’ duration, and most cases of acute pharyngitis (unless group A streptococcal infection is confirmed).

 Bronchitis in children is an acute cough illness that is generally self-limited and caused by viruses.

If the child in the vignette has a positive diagnostic test result (rapid antigen detection or throat culture), antibiotic treatment would be appropriate.

 Penicillin V is the drug of choice for streptococcal pharyngitis, although amoxicillin often is used instead as first-line treatment.

A firstgeneration cephalosporin (eg, cephalexin or cefadroxil) also may be used. Broader-spectrum agents (eg, amoxicillin-clavulanate, second- or third-generation cephalosporins) are not indicated routinely for this infection.

Azithromycin should be reserved for treating streptococcal pharyngitis in the patient who is allergic to penicillins and cephalosporins.

Streptococcal serogroups C and G rarely have been associated with symptomatic pharyngitis. They have not
been associated with rheumatic fever, but antibiotic therapy (same agents as for group A streptococcal infection) may be considered in the symptomatic patient who has a positive culture and no other cause determined for the pharyngitis.


Q3 :

A 12-year-old boy presents with a 5-day history of sore throat, fever, and progressive rightsided neck pain and swelling. On physical examination, his temperature is 40.0°C, he has trismus, the right side of his neck is swollen and tender to palpation, and his chest is clear to auscultation. His white blood cell count is 30.0x103/mcL (30.0x109/L), with 80% polymorphonuclear leukocytes, 15% lymphocytes, and 5% monocytes. Computed tomography scan of the neck reveals a deep parapharyngeal abscess (Item Q141).
Of the following, the MOST appropriate antimicrobial to include in his therapy is

A. ampicillin-sulbactam
B. azithromycin
C. clarithromycin
D. gentamicin
E. trimethoprim-sulfamethoxazole

Answer :

A


The boy described in the vignette has an abscess in the deep tissues of the neck. Streptococci, including S pyogenes, and Staphylococcus aureus are the most common pathogens associated with infections of the parapharyngeal space. However, oral anaerobic bacteria also are found frequently in these infections because the primary portals of entry for organisms into the parapharyngeal space are the oropharynx, lower molars, nasopharynx, paranasal sinuses, and mastoid.

 The most common anaerobic bacteria isolated from parapharyngeal infections are Bacteroides, Peptostreptococcus, and Fusobacterium. Most of these infections are polymicrobial.

 Because the parapharyngeal space is contiguous with the retropharyngeal, submandibular, and peritonsillar spaces, infection may spread in any number of directions and lead to a variety of clinical manifestations and complications.

Ampicillin-sulbactam is a beta-lactamase-resistant semisynthetic penicillin that has activity
against anaerobes, susceptible aerobic gram-positive organisms, and respiratory tract gramnegative
pathogens, making it an appropriate initial drug for the patient described in the vignette.

Because group A streptococci are becoming increasingly resistant to macrolide antibiotics such as azithromycin and clarithromycin and to trimethoprim-sulfamethoxazole, these drugs are not appropriate.

In addition, macrolide antibiotics have less activity than ampicillin-sulbactam against B fragilis and Fusobacterium.

Gentamicin is not useful because aerobic enteric gram-negative rods do not play a significant role in parapharyngeal infections.

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Q 4:

A five year old boy is admitted to the paediatric ward with a two day history of fever, myalgia and jaundice.  His family live on a canal barge and have been moving around the country on a regular basis.  He has many  scabs on his knees and elbows, which his parents say result from his playing on the canal banks.  Observations show temperature 38.7 °C,heart rate 150 beats per minute, respiratory rate 35. He looks unwell but is fully  conscious. He has conjunctival suffusion and scleral icterus. Blood tests show: Haemoglobin 10.5 g/dL,  White cell count 22.5 x109/L,Neutrophils 19x109/L, Platelets 150x109/L, Urea22.5mmol/L,  Creatinine 250 micromol/L, Bilirubin 150 micromol/L, Aspartate Amino-Transferase 350 U/L. The mostlikely diagnosis is: A- Hepatitis B B- Hepatitis A C- Leptospirosis D- Haemolytic uraemic syndrome E- Reye’s syndrome

Answer :

C

Leptospirosis is caused by a spirochete organism, of which there are many serovars. It is contracted by contact with water contaminated with the urine or carcasses of infected animals eg rats. There have been cases in the UK associated with rats around waterways. It may cause asymptomatic infection, or an influenza like illness which may progress to severe disease with jaundice and renal impairment (Weil’s disease). Conjunctival suffusion is characteristic but not always present. Viral hepatitis is characterised by a prodromal phase with fever in those who are symptomatic, followed by hepatitis after the fever declined. Hepatitis A is frequently asymptomatic in children, and hepatitis B rarely causes acute hepatitis. Haemolytic uraemic syndrome typically follows a gastrointestinal disorder with bloody diarrhoea. The commonest aetiologic agent is E Coli 0157:H7. Reye’s syndrome is an acute and often fatal encephalopathy associated with hepatic failure. It is becoming increasingly rare.

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Q 5

A 5-year-old boy is hospitalized in January with fever and seizures. Lumbar puncture reveals clear cerebrospinal fluid that has a white blood cell count of 47/cu mm, all of which are lymphocytes. On physical examination, he appears obtunded but arouses with painful stimuli. Neurologic examination reveals no focal findings.

Of the following, the diagnostic test that is MOST likely to reveal the etiology of this child's illness is:

A.         bacterial culture of cerebrospinal fluid

B.         polymerase chain reaction test of cerebrospinal fluid for herpes simplex

C.         Streptococcus pneumoniae bacterial antigen test of cerebrospinal fluid

D.         viral culture of cerebrospinal fluid

E.         viral culture of nasopharyngeal and rectal swabs

Answer :

B

The boy described in the vignette has symptoms suggestive of encephalitis. These symptoms, combined with the cerebrospinal fluid (CSF) findings, are most consistent with a viral etiology. The most likely pathogen in a sporadic case of viral encephalitis is herpes simplex virus (HSV). 

In the past, HSV encephalitis was diagnosed by culture or direct fluorescence testing of brain biopsy tissue. More recently, polymerase chain reaction (PCR) testing of CSF for HSV DNA has become the preferred diagnostic modality.

 Viral cultures of the CSF for herpes are rarely positive in HSV encephalitis beyond the neonatal period, and the virus is not found in cultures of sites outside the central nervous system.

 Bacterial culture of CSF or use of antigen detection tests for Streptococcus pneumoniae are not likely to be positive in a child whose findings are consistent with encephalitis.

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Q 6 :

A 3-year-old child is brought to the emergency department with a fever of 103.1°F (39.5°C) and diarrhea of acute onset. The stool is guaiac-positive and contains leukocytes. There is no history of foreign travel, and the child has not received antibiotics recently.

Of the following, the organism that is MOST likely to be isolated from this child's stool is:

A.         Clostridium difficile

B.         Giardia lamblia

C.         rotavirus

D.         Salmonella enteritidis

E.         Vibrio cholerae

     Answer:

D

Infectious diarrhea is a common illness among children and is caused by a wide variety of pathogens. The clinical presentation of the child can aid in identifying the likely pathogen. 

Children who have viral diarrheas usually have low-grade fever; vomiting; and large, loose, watery stools. Dehydration commonly accompanies rotavirus infection, which is the most common of the viral diarrheas.

            The symptoms exhibited by the child in the vignette are most consistent with a bacterial diarrhea, such as those caused by Salmonella or Shigella sp. Patients who have these infections often present with high fevers and small, frequent stools that contain mucus or blood. Stool cultures reveal the pathogen, and susceptibility testing of the isolate is useful because many Salmonella and Shigella isolates are resistant to ampicillin and trimethoprim-sulfamethoxazole. Although antibiotic treatment is indicated for Shigella infections, Salmonella gastroenteritis is self-limited in immunocompetent patients, and antibiotic treatment usually is withheld because it may prolong carriage of the organism.

            Clostridium difficile is most common in the setting of antibiotic-induced colitis. 

Vibrio cholerae is acquired from contaminated seafood or water and rarely is seen in the United States. Infection with Giardia lamblia is more likely to result in chronic or persistent diarrhea with malabsorption

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Q 7 :

A 2-year-old girl presents with a swollen, tender, erythematous knee. Two weeks ago she had fever and bloody diarrhea that lasted 4 days.

Of the following, the MOST likely organism to be associated with arthritis in this patient is:

A.  Escherichia coli

B.  Giardia lamblia

C.  Norwalk virus

D.  rotavirus

E.  Shigella flexneri

Answer :

E

Postinfectious or reactive arthritis often occurs several weeks or months after an acute infection. 

Reactive arthritis frequently follows enteric infections with Shigella, Salmonella, Yersinia, and Campylobacter sp. 

As described in the vignette, affected children initially develop bloody diarrhea, followed by the onset of arthritis, typically 1 to 2 weeks after the triggering infection. 

Reactive arthritides are usually acute and self-limited, resolving within weeks or months.

 There is no specific treatment for reactive arthritis. The patient may need analgesics for pain relief. Of the choices listed, Shigella would be the most likely organism to cause bloody diarrhea and arthritis.

            Other important examples of reactive arthritis include postvenereal reactive arthritis (especially with Chlamydia trachomatis) and virus-related arthritis.

 A variety of viruses have been associated with reactive arthritis, including rubella, hepatitis B, mumps, parvoviruses, and herpesviruses. 

Poststreptococcal reactive arthritis and acute rheumatic fever (ARF) are two other examples of reactive arthritis. 

            Reactive arthritis does not typically follow infections with Escherichia coli, Giardia lamblia, Norwalk virus, or rotavirus.

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Q8

A 12-year-old girl who has systemic lupus erythematosus was exposed to varicella 24 hours ago. She has been receiving prednisone 40 mg bid for 9 weeks because of an exacerbation of nephropathy. She has not had varicella or received varicella immunization.

Of the following, the MOST appropriate next step is to:

A.  administer varicella vaccine

B.  administer varicella-zoster immune globulin

C.  begin prophylactic doses of acyclovir

D.  discontinue the prednisone

E.  provide stress doses of prednisone

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Q 9

A 5-year-old girl complains of perianal pruritus. Results of a clear adhesive tape test are positive.

Of the following, the drug of CHOICE for this infection is:

A. iodoquinol

B. ivermectin

C. mebendazole

D. praziquantel

E.  thiabendazole


Answer

C

Perianal pruritus is a common symptom of infection with Enterobius vermicularis (pinworms). 

Although infection may appear in all age groups and socioeconomic levels, it is most prevalent in preschool and school-age children.

            Typically, embryonated eggs are ingested and migrate to the duodenum, where they hatch and undergo sexual maturation before reaching the cecum. Adult pinworms reside in the cecum, emerge at night through the anus, and migrate to the perianal region, where gravid females deposit their eggs and die. The eggs cause anal pruritus, which leads to scratching and accumulation under the fingernails, thereby promoting autoinfection and spread to close contacts. The eggs remain infective for 2 to 3 weeks. Aberrant migration of the adult worm from the perineum rarely may give rise to urethritis, vaginitis, salpingitis, or pelvic peritonitis.

            Some physicians treat the infestation based only on the history, but a definitive diagnosis should be made. Eggs are detected easily on clear adhesive tape that is applied to the perianal area early in the morning on awakening. The tape is applied to a slide and viewed under a low-power microscopic lens. Repeated examinations on successive mornings may be necessary. Because Enterobius vermicularis eggs are not excreted in the stool, examination of feces is not a useful test.

            The drugs of choice for treatment of enterobiasis are either mebendazole (100 mg regardless of weight), pyrantel pamoate (11 mg/kg, not to exceed 1 g), or albendazole (400 mg) administered as a single dose. Because none of these drugs is completely effective against eggs or developing larvae, a second treatment 2 weeks after the first is recommended. Frequently, all family members are treated in an attempt to break the cycle of reinfection. 

Because pinworm infection often carries substantial unwarranted social stigma, reassurance of families that this infection is very common, often recurs, and does not reflect uncleanliness is an important component of therapy.

            Reinfection with pinworms occurs easily. Measures that may reduce egg contamination of the local environment are helpful and include:

            • having the infected person bathe in the morning, which removes a large proportion of the eggs;

            • frequent changing of the infected person’s underclothes, bed clothes, and bedsheets;

            • hygienic measures such as washing hands prior to eating or preparing food, keeping fingernails short, and avoiding nail biting.

            Measures such as cleaning or vacuuming the entire house or washing bed clothes and bedsheets daily are not necessary.

            Mebendazole also is an effective treatment for other roundworm infections, such as ascariasis, capillariasis, hookworm infections, trichinosis, whipworm infections, and visceral larva migrans. Iodoquinol is used to eradicate intestinal carriage of Entamoeba histolytica. Ivermectin is recommended for treatment of cutaneous larva migrans, river blindness (infection with Onchocerca volvulus), and strongyloidiasis. Praziquantel is the drug of choice for treatment of fluke and tapeworm infections, such as schistosomiasis and cysticercosis. Thiabendazole is effective in treating strongyloidiasis and cutaneous larva migrans.

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Q 10

A 2-year-old boy presents with rales, pallor, chronic failure to thrive, recurrent thrush, diarrhea, and oxygen saturation of 84% on room air. Echocardiography demonstrates an enlarged left ventricle with diminished systolic function.

Of the following, the blood test MOST likely to establish the diagnosis in this child is:

A.  antibody testing for Epstein-Barr virus

B.  antibody testing for human immunodeficiency virus

C.  antibody testing for human parvovirus

D.  serum carnitine level

E.  serum selenium level

Answer

B

It is now appreciated that varying degrees of myocardial dysfunction are common in human immunodeficiency virus (HIV) infection in children, especially when the infection has reached the point of clinical immunodeficiency. Pallor is common in affected children from the combination of anemia and congestive heart failure. Diarrhea probably is related more to the acquired immunodeficiency syndrome (AIDS) than to the cardiomyopathy. The unusually low oxygen saturation may be explained by interstitial pneumonitis, sometimes due to Pneumocystis jiroveci (carinii)  infection. Although maternal HIV screening and treatment have decreased significantly the number of children who present in the first few years of life with cardiomyopathy and frank AIDS symptoms, cases still do occur in clinical practice.

            It has been proposed that the dilated cardiomyopathy of childhood AIDS is due primarily to chronic viral myocarditis from coxsackievirus, adenovirus, or cytomegalovirus that is not cleared effectively by the damaged immune system.

            Epstein-Barr viral infection of the myocardium has bee

n diagnosed by polymerase chain reaction analysis of myocardial biopsy in some children who have dilated cardiomyopathy. Clinical signs of Epstein-Barr virus-related myocarditis are not specific and include cardiomegaly, poor systolic left ventricular function, and physical signs of congestive heart failure.

            Human parvovirus may cause a number of clinical illnesses, including erythema infectiosum (“fifth disease”) or papulopurpuric “gloves and socks” syndrome. It does not have any important association with myocarditis.

            Serum carnitine levels may be normal or decreased in children who have cardiomyopathy from a variety of causes. Low serum carnitine concentrations do not define or suggest a single specific etiology in cardiomyopathy.

            Selenium deficiency is a rare mineral deficiency disorder believed to be associated with cardiomyopathy. Some investigators believe that selenium deficiency is common in AIDS and postulate a role for it in the cardiac dysfunction of AIDS infection. However, as noted previously, others believe that chronic viral infection 

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Q 11

A 10 year old child  has just been diagnosed with meningococcal meningitis.

In discussing chemoprophylaxis with his family, you are MOST likely to include the statement that rifampin:

A.  causes a reactive arthritis

B.  causes discoloration of body fluids

C.  decreases the reliability of depot medroxyprogesterone

D.  is contraindicated if she has asthma

E.  is safely used during pregnancy

Answer

B

            Rifampin penetrates the central nervous system and is found in most body fluids. It can cause orange-colored secretions, including urine, sweat, and tears. Patients should be advised that contact lenses may be stained orange.

            Rifampin is metabolized by the liver and excreted in bile and urine. It can alter the serum concentrations of many drugs and possibly interfere with the efficacy of oral contraceptives. The reliability of intramuscular medroxyprogesterone is not altered with rifampin use. Neither rifampin nor ciprofloxacin is recommended for use during pregnancy. A single intramuscular dose of ceftriaxone is the recommended prophylaxis during pregnancy.

            Rifampin therapy is not contraindicated for patients who have asthma, although its use may decrease the efficacy of corticosteroids. Reactive arthritis is not a common adverse reaction associated with rifampin.

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Q 11

A child who has acute myelogenous leukemia is being treated for Pseudomonas bacteremia with intravenous doses of piperacillin and gentamicin. Gentamicin levels are measured after 2 days of therapy.

How long after completing a 30-minute infusion should blood for peak gentamicin concentrations be drawn?:

A. 30 minutes

B. 60 minutes

C. 90 minutes

D. 120 minutes

E. 150 minutes

Answer

B

Therapeutic drug monitoring is used to prevent or decrease the risk of toxic effects of medication. Monitoring serum concentrations of most antibiotics is unnecessary because these drugs are effective over a wide range of serum levels, therapeutic levels are achieved easily, and levels associated with toxicity rarely are encountered when standard dosing schedules are employed and patients have normal clearance mechanisms. However, certain antibiotics, especially chloramphenicol, vancomycin, and the aminoglycosides, have narrow therapeutic windows and are associated with potential adverse reactions. Therefore, careful monitoring of serum concentrations of these drugs is critical.

            Measurement of serum drug levels can help determine the dose and frequency of administration that allow for maximum therapeutic benefit with minimum toxicity. Appropriately timed blood samples are essential for accurate interpretation of serum drug levels. The best times to obtain blood samples for most parenterally administered antibiotics is 30 minutes after a 20- to 30-minute intravenous infusion, when the level is presumed to be highest (peak level), and immediately before the next dose, when the level is presumed to be lowest (trough level). For oral antibiotics, peak levels should be obtained 30 minutes to 1 hour after oral liquid or 1.5 hours following oral capsule administration.

            The principles of therapeutic drug monitoring are based on two pharmacokinetic parameters: volume of distribution (Vd) and half-life (t1/2). Vd is the hypothetical volume within which the drug is distributed and is used to determine the dose required to maximize activity. The t1/2 reflects the rate of drug elimination and, thus, is used to determine the most appropriate frequency of dosing. The blood sample obtained 1 hour after completing the infusion provides information about the Vd after the drug has begun to be dispersed through the body but before significant amounts have been eliminated. The trough level, drawn immediately before the next dose, helps to determine elimination kinetics and t1/2.

            A level drawn 30 minutes after completing a gentamicin infusion will not be a reliable indicator of Vd because not enough time has passed for drug distribution to begin. Serum samples drawn 90, 120, or 150 minutes after completing the infusion are not as reliable as a sample obtained 1 hour after completing the infusion because drug elimination will have begun.

            Aminoglycoside antibiotics (eg, gentamicin, tobramycin, amikacin) have a high profile of toxic side effects, such as nephrotoxicity and ototoxicity. Although aminoglycoside-induced renal injury usually is reversible, ototoxicity, characterized by both auditory and vestibular nerve damage, is not. Individual risk factors may contribute to the development of toxicity, but the major association with organ damage is elevated peak and trough serum drug concentrations. Sustained peak serum gentamicin concentrations of more than 12 to 14 mg/L and trough serum concentrations of more than 2 mg/L have been associated with a significantly increased risk of both toxicities.

            Monitoring of serum aminoglycoside peak and trough concentrations has been shown to decrease the incidence of nephrotoxicity, although these toxicities still can occur in patients whose serum concentrations are in the desired therapeutic range. Thus, regular monitoring of levels is recommended to assure the adequacy of the dosing regimen and to monitor for drug accumulation and potential toxicity. Serial trough concentrations correlate better than peak levels with the rising tissue accumulation of drug during a course of treatment.

            Peak and trough serum concentrations should be measured following the fifth or sixth dose of the aminoglycoside. If these levels are appropriate, serial trough concentrations should be obtained every 4 to 7 days, depending on the clinical status of the patient. Sustained elevation of the trough concentration in excess of 25% over a 2- to 4-day period has been found to place patients at measurable risk for aminoglycoside-induced toxicity.

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Q12

A child is bitten on the hand by a neighbor's dog. Within 24 hours there is erythema, pain, and swelling at the site of the bite. The child is taken to the emergency department where cultures are taken of sanguinopurulent drainage from the wound.

Of the following, the MOST likely organism infecting the wound is:

A. Eikenella corrodens

B. Francisella tularensis

C. Pasteurella multocida

D. Staphylococcus aureus

E. Streptococcus pyogenes

Answer

C

Pasteurella multocida is the organism most likely to infect animal bite wounds. Clinical infection with P multocida is characterized by the rapid evolution of an intense inflammatory response, with substantial pain and swelling developing within 24 hours of the initial injury in 70% of cases and by 48 hours in 90% of patients who develop an infection. P multocida infection has resulted in abscess formation, septic arthritis, osteomyelitis, sepsis, meningitis, endocarditis, and pneumonia. Infections usually exhibit localized cellulitis and purulent discharge. Fever, regional adenopathy, and lymphangitis are seen in fewer than 20% of patients.

The drug of choice for treatment of P multocida infections is penicillin. Other effective agents include ampicillin, amoxicillin-clavulanate, cefuroxime, cefpodoxime, trimethoprim-sulfamethoxazole, and tetracycline. For patients allergic to beta-lactam agents, tetracycline is effective, but it should not be administered to children younger than 8 years of age.