Human herpes virus 6 is a ubiquitous virus that infects most children before the age of 3 years, although most infections are asymptomatic. The virus has an incubation period of 1-2 weeks and causes an illness associated with fever and mild respiratory symptoms, which lends to last for no longer than 5 days. Following defervescence, a characteristic rash appears suddenly. It is an erythematous maculopapular eruption that starts on the trunk and spreads rapidly to the extremities, with sparing of the face. The rash tends to disappear in 1-2 days. The diagnosis is primarily clinical, based on the history and examination. Because of the short-lived nature of the disease, no treatment is usually required other than reassurance.
The varicella zoster virus is a highly contagious virus that causes two clinical syndromes. Chickenpox is the more common childhood infection. A typical case of chickenpox includes a fever and a rash, which tends to develop in clusters. The initial exanthem is often papules or vesicles on an erythematous base, described as "dewdrops on a rose petal." The vesicles then progress to shallow, crusted erosions. Patients may also develop enanthems, with lesions on the oral, nasal, or gastrointestinal mucosa. In rare cases, serious complications may develop, which include encephalitis, meningitis, and pneumonitis. The diagnosis is usually clinical, but may be confirmed with Tzanck smear or identification of the virus on DNA probe testing. Antiviral therapy using acyclovir, valacyclovir, or famciclovir may shorten the course of the illness if started within 72 hours of onset. Varicella vaccination is now universally recommended at age 12-18 months and has significantly reduced the incidence of childhood chickenpox.
Shingles is a reactivation of the varicella virus, which can remain cfortuatic in a dorsal root ganglion following the initial infection. The reactivated virus causes a vesicular eruption, usually along a single dermatome and not crossing the midline. The reaction can occur at any age. but is more common in the elderly or immunosuppressed. The rash can be extremely painful and can result in a neuralgia that lasts long after resolution of the rash. Antiviral therapy started within 72 hours of the rash may reduce the incidence of the postherpetic neuralgia.
Parvovirus B19 causes a characteristic syndrome known as erythema infectiosum or fifth disease. This virus tends to infect children younger than 10 years of age and occurs most commonly in the winter or spring. The rash usually starts as confluent erythematous macules on the face, which usually spares the nose and periorbital regions. This gives the classic "slapped cheek" appearance that is commonly diagnostic of the infection. The facial rash lasts for 2-4 days, followed by lacy, pruritic exanthem on the trunk and extremities that usually lasts for 1-2 weeks, but can have a relapsing course for several months. Parvovirus BI9 tends to cause a more severe illness, with rheumatic complaints such as arthritis. The virus can be transmitted from mother to fetus during pregnancy, resulting in fetal hydrops and pregnancy loss.
Common Bacterial Infections Group A p-Hemolytie Streptococcus
Group A P-hemolytic Streptococcus (GAS) is associated with numerous diseases, particularly in children. It is the causative agent of streptococcal pharyngitis and its complications, which include rheumatic fever and glomerulonephritis. It can also cause a cellulitis of the skin.
The rash of scarlet fever usually starts about 2 days after the onset of sore throat. The rash consists of punctate, raised, erythematous eruptions that can become confluent and feel like sandpaper. The rash tends to start on the upper trunk and spreads to the rest of the trunk and the extremities. The exanthem can also be associated with an enanthem, causing the appearance of a "strawberry tongue." The rash fades and desquamation occurs 4—5 days after the first appearance of the rash.
GAS infections can be confirmed by rapid antigen testing or culture from a throat swab. The first-line treatment for GAS infections is penicillin, with cephalosporins or macrolides as alternatives in the penicillin allergic.
The meningococcus causes an acute, life-threatening infection, often associated with a rash. Meningococcemia can cause a severe illness with high fevers, hypotension. and altered mental status. Most people with meningococcemia progress to develop frank meningitis, with its associated signs of meningeal irritation. The rash of meningococcemia often starts as an erythematous maculopapular eruption that progresses to form peteehiae.
Someone with suspected meningococcemia should be immediately hospitalized, usually in the intensive care unit. The ABCs (Airway, Breathing, and Circulation) should be urgently evaluated, blood and cerebrospinal fluid cultures collected, and empiric antibiotic therapy instituted. A common regimen includes vancomycin and ceftriaxone, with adjustments based on culture results. A meningococcal vaccine is now recommended for routine childhood immunization and also should be offered to patients at risk for the disease (asplenic, those living in dormitories or military barracks). Close contacts of someone with meningococcal infection should be offered prophylaxis with rifampin.
Rocky Mountain spotted fever (RMSF) is an acute, life-threatening infection caused by the organism Rickettsia rickettsii, which is transmitted via a tick bite. The infection occurs more often in the summer months, when people are more likely to be outdoors. The illness causes acute fever, headache, myalgia, and fatigue. The classic exanthem is a macular, papular, or petechial eruption that starts on the wrists and ankles. Laboratory tests often show a low white blood cell count, low platelet count, and elevated liver enzymes. The diagnosis is confirmed with serology, but this is not helpful in the acute setting. Suspected RMSF should be treated empirically with doxycycline.
Lyme disease is endemic in many areas of the United States, including New England and the Mid-Atlantic regions. The causative spirochete, Borrelia burgdorferi, is transmitted via bite of the Ixodes tick. Because the tick is very small, infected persons are often unaware of a history of a tick bite. The characteristic rash, erythema migrans, develops 3-30 days following infection. The exanthema is typically an expanding erythematous macule with central clearing, often described as appearing like a "bull's-eye." In this stage of disease, treatment with oral doxycycline can prevent progression to the more serious complications of Lyme disease, including arthritis, carditis, and complete heart block. The diagnosis can be confirmed with serologic studies.
|48.I] A 6-year-old is brought to your office with a fever and upper respiratory symptoms. On examination, he is noted to have a low-grade fever, a normal general examination, and an erythematous macular eruption on his cheeks. Which of the following is the most likely causative organism?
A. Varicella zoster virus
B. Parvovirus B19
C. Human herpes virus 6
[48.2] A 10-year-old is found to have an exudative pharyngitis and a fine, sand-papery eruption on his trunk. He is allergic to no medications. Which of the following is the most appropriate first-line treatment?
B. Vancomycin and ceftriaxone
[48.3] You are called to see a 16-year-old in the emergency department. His parents say that he acutely developed fever, chills, and rash. He has been confused and not answering their questions. On examination he is toxically ill appearing, and is febrile, tachycardic, and hypotensive. He is noted to have a diffuse petechial rash. What is the most likely diagnosis?
B. Rocky Mountain spotted fever
C. Scarlet fever
D. Lyme disease
|48.1| B. Erythema infectiosum, fifth disease, characteristically causes the "slapped cheek" appearance described in this question. It is caused by parvovirus BI9.
|48.2] I). Scarlet fever, caused by GAS infection, should be treated with penicillin in those who are not allergic to it. A macrolide, like erythromycin. is an alternative for use by the penicillin-allergic patient.
|48.31 A- This acute, severe illness is consistent with meningococcemia. This adolescent should be admitted to the ICU. his hypotension aggressively managed, and antibiotics started. His family should receive prophylactic therapy with rifampin.
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