Infectious diseases
Scarlet fever
Definition: a bacterial upper respiratory tract infection associated with rash, caused by
group A beta-hemolytic streptococci (GAS), which produce pyogenic toxins.
• Scarlet fever usually occurs after the age of 3 years.
Diagnosis & treatment
• Incubation period: 1-7 days.
• URT features:
o Symptoms: acute onset of fever, sore throat, cough with
abdominal pain & vomiting.
o Signs: the tonsils are hyperemic & edematous & covered by a
white-gray exudate or membrane.
• Rash:
o Usually appears 24-48 hrs. after the onset of the respiratory
symptoms (however, it may be the earliest sign of the
infection).
Clinical o It's diffuse, erythematous, fine papular eruption with
presentation characteristic "goose-pimple appearance" & rough sensation
on palpation.
o Starts around the neck and spreads to the trunk & extremities,
it's most intense in the axilla & groin.
• The face is spared, but there's flushing of the cheeks
with circumoral pallor.
• The tongue is coated with a white coat.
• Resolution:
o The rash starts to disappear after 3-4 days by desquamation.
o The white coat of the tongue begins to desquamate leaving a
red tongue with a "strawberry appearance".
1. Viral exanthems (measles, rubella, roseola infantum &
DDX enteroviruses).
2. Drug eruption.
• Serology: ASO titer (indicates recent infection).
Investigations
• Throat swab for culture (however, some people are carriers).
Page | 1
, Infectious diseases
Body Oral penicillin V (bid for Benzathine penicillin G
weight 10 days) (single dose)
Treatment
> 30 Kg 250 mg 600,000 IU
< 30 Kg 500 mg 1,200,000 IU
Roseola infantum
Definition: a viral URTI caused by human herpes virus (HHV-6).
• Peak incidence: 6-15 months.
Diagnosis & treatment
• Prodromal period: asymptomatic (mostly) or with mild URTI.
• Fever: high-grade (39.5-40 C), may be accompanied by
irritability, anorexia or seizure.
Clinical o It persists for 3-4 days, then resolves abruptly.
presentation • Rash:
o Appears within 12-24 hrs. after the resolution of fever.
o It starts at the trunk then spreads to the face, neck &
proximal extremities.
1. Scarlet fever.
DDX 2. Viral exanthems (measles, rubella).
3. Drug eruption.
• The diagnosis is mainly clinical.
Investigations
• CBC: leukopenia with relative lymphocytosis.
Treatment • Supportive measures (antipyretics for fever).
Note:
• Exanthem: rash on the skin.
• Enanthem: rash on the mucous membranes.
Page | 2
, Infectious diseases
Diphtheria
Definition: an acute bacterial (toxic) infection caused by Corynebacterium diphtheriae
(non-encapsulated, aerobic, spore forming, gram positive bacilli).
Transmission:
• Respiratory droplets.
• Contact with infected skin lesions (in cutaneous diphtheria).
Pathogenesis:
The major virulence of the organism is its ability to produce an exotoxin, which inhibits the
protein synthesis in the infected tissues, resulting in total tissue necrosis.
Diagnosis & treatment
• The clinical presentation is influenced by:
a. The anatomical site of the infection, the 2 most common sites:
• Pharynx & tonsils (94 %).
• Nose & larynx.
b. The systemic distribution of the toxin.
c. The immunity of the patient.
• Respiratory tract diphtheria:
o Incubation period: 2-4 days.
Clinical
o Symptoms: sore throat +/- fever (50 % only).
presentation
o On examination:
• Unilateral or bilateral tonsillar membrane (thick, gray-
white membrane adherent to the underlying tonsil).
• Soft tissue edema & LAP with characteristic "bull-neck
appearance".
• Cutaneous diphtheria:
o Superficial, ecthyma-like, non-healing ulcer with gray-brown
membrane, it's erythematous & very painful.
1. Respiratory tract obstruction (may require bronchoscopy or
intubation).
Complications
2. Toxic cardiomyopathy:
• Incidence: 10-15 %.
Page | 3
Scarlet fever
Definition: a bacterial upper respiratory tract infection associated with rash, caused by
group A beta-hemolytic streptococci (GAS), which produce pyogenic toxins.
• Scarlet fever usually occurs after the age of 3 years.
Diagnosis & treatment
• Incubation period: 1-7 days.
• URT features:
o Symptoms: acute onset of fever, sore throat, cough with
abdominal pain & vomiting.
o Signs: the tonsils are hyperemic & edematous & covered by a
white-gray exudate or membrane.
• Rash:
o Usually appears 24-48 hrs. after the onset of the respiratory
symptoms (however, it may be the earliest sign of the
infection).
Clinical o It's diffuse, erythematous, fine papular eruption with
presentation characteristic "goose-pimple appearance" & rough sensation
on palpation.
o Starts around the neck and spreads to the trunk & extremities,
it's most intense in the axilla & groin.
• The face is spared, but there's flushing of the cheeks
with circumoral pallor.
• The tongue is coated with a white coat.
• Resolution:
o The rash starts to disappear after 3-4 days by desquamation.
o The white coat of the tongue begins to desquamate leaving a
red tongue with a "strawberry appearance".
1. Viral exanthems (measles, rubella, roseola infantum &
DDX enteroviruses).
2. Drug eruption.
• Serology: ASO titer (indicates recent infection).
Investigations
• Throat swab for culture (however, some people are carriers).
Page | 1
, Infectious diseases
Body Oral penicillin V (bid for Benzathine penicillin G
weight 10 days) (single dose)
Treatment
> 30 Kg 250 mg 600,000 IU
< 30 Kg 500 mg 1,200,000 IU
Roseola infantum
Definition: a viral URTI caused by human herpes virus (HHV-6).
• Peak incidence: 6-15 months.
Diagnosis & treatment
• Prodromal period: asymptomatic (mostly) or with mild URTI.
• Fever: high-grade (39.5-40 C), may be accompanied by
irritability, anorexia or seizure.
Clinical o It persists for 3-4 days, then resolves abruptly.
presentation • Rash:
o Appears within 12-24 hrs. after the resolution of fever.
o It starts at the trunk then spreads to the face, neck &
proximal extremities.
1. Scarlet fever.
DDX 2. Viral exanthems (measles, rubella).
3. Drug eruption.
• The diagnosis is mainly clinical.
Investigations
• CBC: leukopenia with relative lymphocytosis.
Treatment • Supportive measures (antipyretics for fever).
Note:
• Exanthem: rash on the skin.
• Enanthem: rash on the mucous membranes.
Page | 2
, Infectious diseases
Diphtheria
Definition: an acute bacterial (toxic) infection caused by Corynebacterium diphtheriae
(non-encapsulated, aerobic, spore forming, gram positive bacilli).
Transmission:
• Respiratory droplets.
• Contact with infected skin lesions (in cutaneous diphtheria).
Pathogenesis:
The major virulence of the organism is its ability to produce an exotoxin, which inhibits the
protein synthesis in the infected tissues, resulting in total tissue necrosis.
Diagnosis & treatment
• The clinical presentation is influenced by:
a. The anatomical site of the infection, the 2 most common sites:
• Pharynx & tonsils (94 %).
• Nose & larynx.
b. The systemic distribution of the toxin.
c. The immunity of the patient.
• Respiratory tract diphtheria:
o Incubation period: 2-4 days.
Clinical
o Symptoms: sore throat +/- fever (50 % only).
presentation
o On examination:
• Unilateral or bilateral tonsillar membrane (thick, gray-
white membrane adherent to the underlying tonsil).
• Soft tissue edema & LAP with characteristic "bull-neck
appearance".
• Cutaneous diphtheria:
o Superficial, ecthyma-like, non-healing ulcer with gray-brown
membrane, it's erythematous & very painful.
1. Respiratory tract obstruction (may require bronchoscopy or
intubation).
Complications
2. Toxic cardiomyopathy:
• Incidence: 10-15 %.
Page | 3
