Viral

Herpes

(Herpesvirus 6)

A 1 year old boy comes into the pediatrician's office with a skin rash. His mother says that 4 days ago, he had a fever of about 105°F. The fever suddenly dropped. As fever disappeared the skin rash began first on the trunk. His mother also reports that the child has been unwilling to eat and has been irritable. On physical examination, you find a maculopapular, nonpruritic rash that blanches on pressure. Rash appears as very slightly elevated, rose-pink papules that appear profusely on trunk, arms and neck; mild on face and legs. There is lymphadenopathy in cervical and posterior auricular regions. The mother reports that the boy goes to day care.

Laboratory: Tissue culture or blood sample and PCR reveals DNA enveloped virus.

Discussion: Diagnosis of roseola infantum (aka exanthem subitum) is by clinical presentation, tissue culture and PCR of the serum. It is the most common exanthematous disease in infants 2 years of age or younger and frequently causes febrile convulsions.

Measles

(Measles virus)

A 12 year old boy comes to the pediatrician presenting with brassy cough, coryza, and conjunctivitis, fever, malaise, and photophobia. History of present illness reveals that a few days ago his mother found minute, whitish spots over buccal/labial mucosa that rapidly increased in number and coalesced. Red, morbilliform, blanching rash.

Laboratory: Unsegmented ssRNA with a helical nucleocapsid on viral isolation in tissue culture.

Discussion: Diagnosis is made by clinical presentation. Tissue culture can be performed but rarely done. Koplik spots in the mouth are pathognomonic. Patients are contagious from 2 days before symptoms to 4 days after onset of rash.

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Rubella

(Togavirus)

A 12 year old boy is brought into the pediatrician's office by his father for complaints of low-grade fever, coryza, malaise, rash and polyarthralgia/polyarthritis. His father reports that the rash began on the face and then spread to the trunk. Physical exam reveals soft palate petechiae (Forschheimer's sign).

Laboratory: Fourfold rise in serum levels of antibody to ssRNA virus with an icosahedral nucleocapsid. Virus is able to interfere with echovirus cytopathic effect (CPE).

Discussion: Diagnosis of rubella (aka German measles) is made by clinical presentation and labs. There is a live, attenuated virus vaccine available that should not be given to pregnant women although it has not been associated with teratogenic effects. The disease in pregnant women results in severe birth defects so all children should be vaccinated.

Chickenpox

(Varicella-Zoster virus)

The pediatrician's office is getting a large number of patients with a similar clinical presentation. The middle school aged children present with a rash that looks like "teardrop" vesicles on erythematous bases. The lesions progress from macule to papule to vesicle and then begin to crust. The rash is pruritic and usually begins on the trunk and then spreads to face and scalp. There is minimal involvement of the extremities. Interestingly, these children attend the same school.

Laboratory: Tzanck smear shows multinucleated giant cells with intranuclear inclusions. Enveloped dsDNA virus found on viral cell culture.

Discussion: The diagnosis of chickenpox by Varicella-zoster virus (VZV) is made clinically however labs can be used to confirm the results. Chickenpox is a common, highly contagious, childhood exanthem characterized by the development of typical crops of vesicles on the skin and mucous membranes. The virus is spread by respiratory droplets or direct contact with vesicles or indirectly through freshly soiled articles. Most people acquire chickenpox during childhood and develop long lasting immunity. Human (alpha) herpesvirus 3 (varicella-zoster virus, V-Z virus) is a member of the Herpesvirus group. Varicella (Chickenpox) is the primary disease while Zoster (shingles) is the recurrent form and occurs in older or immunocompromised patients. A vaccine is available.

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Fifth's disease

(B-19 virus)

A 28 year old woman pregnant with her second child comes to her obstetrician with a rash on her face looking like someone has "slapped" her. She denies physical abuse. A week ago, her 4 year old had a similar rash that spread to the trunk and extremities.

Laboratory: She has a titer of anti-B19 IgM.

Discussion: B19 is a parvovirus with circular, ssDNA. It is the only pathogenic parvovirus. It is serious in pregnant women and can cause fetal death due to erythrocyte lysis.

Fungal

Ringworm

(Trichophyton rubrum)

A 34 year old veterinarian present to the clinic with rash and mild pruritus. The scaling plaques are circular, bright red, sharply marginated, and occur in groups. Each plaque is less than 5 cm in diameter. She says the plaques are extremely itchy. Hyperpigmentation is present.

Laboratory: Potassium hydroxide preparation of skin scrapings show long septate hyphae . Fungal culture may be obtained, but is not generally necessary.

Discussion: The diagnosis of tinea corporis (ringworm) is made by clinical presentation and labs.

Bacterial

Rocky Mountain Spotted Fever

(Rickettsia rickettsii)

A 22 year old female comes into your office with fever, rash, headache, and nausea and vomiting. She had been camping over the past weekend. On further questioning, she reports that the rash began peripherally but now involves the entire body including her palms and soles. She remembers being bitten by a tick.

Laboratory: Antigens crossreact with serum Proteus vulgaris Ox-19 antibody (Weil-Felix reaction). There is also fourfold increase (acute and convalescent) or solitary titer > 1:320

Discussion: Diagnosis of Rocky Mountain Spotted Fever caused by Rickettsia rickettsii is by clinical presentation and the Weil-Felix reaction. Stain and culture rarely done. The organism is transferred by the dog tick which serves as both vector and reservoir.

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Lyme Disease

(Borrelia burgdorferi)

A 34 year old female comes into the clinic complaining of fever, headache, myalgias, and arthralgias. It is the month of August and she has just returned from a camping trip to Connecticut. Physical exam reveals erythema chronicum migrans, a spreading, nonpruritic, circular red rash with a clear center at the site of a tick bite. The rash is painless.

Laboratory: Serological detection with ELISA for IgM and IgG antibodies or observation of irregular loosely coiled spirochetes in skin biopsies.

Discussion: Diagnosis of Lyme disease by Borrelia burgdorferi is made by serological detection with ELISA and clinical presentation. Cultures are rarely useful. Infection with the spirochete Borrelia burgdorferi is transmitted by the bite of Ixodid ticks. Regions at risk include the North Atlantic seaboard and the northern Midwestern states. The months of highest risk are August and September. A vaccine is now available.

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Secondary Syphilis

(Treponema pallidum)

A 19 year old female student comes into the student health clinic complaining of a maculopapular rash on the palms and soles of her body. The rash is bilaterally symmetric, polymorphic, and palpable a with "fresh cut ham" color. It is not pruritic. There are also some moist, flat, pink, peripheral warty lesions on her vulva. She also reports some hair loss on her scalp. She recalls that 2 weeks ago there was a local, nontender ulcer (chancre) on her labia that resolved spontaneously. She admits to being an IV drug user.

Laboratory: Spirochete on darkfield and immunoflourescence microscopy. FTA-ABS positive. VDRL positive.

Discussion: The clinical presentation and labs diagnose primary syphilis caused by Treponema pallidum. The primary and secondary stages are infectious. The moist lesions on genitalia are called condylomata lata. In secondary syphilis, alopecia of scalp, eyebrows and beard is common. Risk factors include multiple sexual partners, exposure to infected body fluids, IV drug use, and transplacental exposure.

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Scarlet Fever

Streptococcus pyogenes (Group A beta-hemolytic)

A 23 year old female comes into the office complaining of something that looks like "sunburn with goose pimples" on her abdomen. History of present illness includes sore throat, headache, vomiting, and fever 2 days ago. Physical exam reveals orange-red punctate skin eruption with sandpaper-like texture. Initially, it covered her chest and axillae, then it spread to her abdomen and extremities.

Laboratory: Swab culture from pharynx grows beta-hemolytic gram positive cocci colonies that are sensitive to bacitracin.

Discussion: The diagnosis of the morbilliform rash caused by Streptococcus pyogenes (Group A beta-hemolytic) is made by clinical presentation and labs. Throat culture leads to the definitive diagnosis. Rapid Strep antigen tests is diagnostic if positive, but sensitivity only 50-90%, so you must do a throat culture if results are negative.

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Toxic Shock Syndrome

Staphylococcus aureus

A 24 year old female is brought to the emergency room by her friend who found her unconscious at home. She is feverish and hypotensive with a diffuse erythematous eruption that looks strikingly similar to the rash of scarlet fever. Additionally, there are areas of desquamation of her palms and soles. She is extremely disoriented but able to report muscle pains and painful urination. She is also currently experiencing menstrual cycle bleeding. You astutely ask her whether she uses tampons or feminine napkins.

Labs: Culture on blood agar reveals gram positive cocci that is catalase and coagulase positive.

Discussion: The diagnosis of toxic shock syndrome by Staphylococcus aureus is made by clinical presentation. Blood culture is confirmatory. TSS is an acute febrile illness that presents with a (1) generalized scalatiniform eruption, (2) hypotension, (3) functional abnormalities of three or more organ systems and (4) desquamation in the evolution of skin lesions. Over 90% of cases occur in menstruating females who use tampons. The organ systems involved include muscle, kidney, CNS, liver, and blood as thrombocytopenia. Staphylococcus aureus is also the cause of brain abscesses, scalded skin syndrome, and pneumonia. It is also responsible for a majority of cases of acute bacterial endocarditis in IV drug abusers.

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Meningitis

Neisseria meningitidis

A 12 year old boy is brought to the emergency room with recent onset fever, severe headache, irritability and malaise. His parents report a history of present illness that includes neck stiffness and projectile vomiting. When the child is disrobed during the physical exam, 2 mm in diameter lesions best described as petechial rashes is found by the elastic portion of his underwear as well as on the trunk and lower portions of the body.

Labs: Culture on blood agar reveals gram negative diplococci that grows on Thayer-Martin media. Lumbar puncture reveals cloudy CSF, neutrophilic pleocytosis, decreased glucose, and increased protein.

Discussion: The diagnosis of meningitis is made by clinical presentation with lumbar puncture and blood culture as confirmatory tools. In patients who present with fever, headache, and neck stiffness, lumbar puncture must be done as soon as increased intracranial pressure has been ruled out. Neisseria meningitidis is the causative agent of meningitis that is associated with a petechial skin rash. Meningitis caused by S. pneumoniae is assocated with sickle cell anemia. The lesions of Neisseria meningitidis may actually be secondary to small subcutaneous hemorrhages. They can be vesicular and desquamate as patients recover.

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