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USMLE STEP2 Exam
Step2 (Page 24 )

Updated On: 30-Jan-2026
Page 24 of 149
PDF with 738 Questions

Select the appropriate incubation period of the Rubella infectious disease of childhood.

  1. 16 days
  2. 78 days
  3. 810 days
  4. 1021 days
  5. 3050 days
  6. 120180 days

Answer(s): D

Explanation:

The incubation period for diphtheria is 17 days. The incubation period for chicken pox is 1021 days, average 14. Infectious mononucleosis, caused by the Epstein-Barr virus, has an estimated incubation period of 3050 days. The incubation period following infection by the mumps virus is usually 1618 days but, like chicken pox, may vary from 14 to 25 days. Pertussis has a shorter incubation period, usually 710 days, with a variation of 421 days. The usual period from contamination with tetanus spores to clinical symptoms is generally 68 days. For rubella, the incubation period is from 14 to 21 days, but usually ranges from 16 to 18 days.



Select the organism associated with the following clinical findings:

A male student returns from traveling to a developing country, with a complaint of eructation, abdominal cramps, and diarrhea for the past 2 weeks, and has lost 10 lbs.

  1. aureus
  2. beta-hemolytic Streptococcus
  3. respiratory syncytial virus (RSV)
  4. Mycoplasma pneumoniae
  5. Haemophilus pertussis
  6. Helicobacter pylori
  7. Escherichia coli
  8. Rickettsia prowazekii
  9. Giardia lamblia
  10. C. perfringens

Answer(s): I

Explanation:

Giardiasis may cause cramping and a chronic diarrheal syndrome, with malabsorption and weight loss. Its distribution is worldwide, particularly where hygienic standards are not high. It also occurs sporadically in high-risk individuals. Streptococcal pyoderma, including erysipelas and impetigo, has been demonstrated to precede acute glomerulonephritis. Even when appropriate antibiotics are given in adequate dosage and duration for these conditions, renal damage may still result. Prevention thus consists of wound care, including cleaning wounds well and removal of crust. Mycoplasma infections are particularly common in families with younger children. They are frequently imported to the family by school-aged children, leading to a low-grade fever and persisting tracheobronchitis in the parents, or more acutely, an atypical pneumonia. G. lamblia is found in up to 20% of homosexual males, and may cause chronic diarrhea, although in these patients it tends to be asymptomatic. E. coli was first reported as a cause of watery diarrhea in nurseries in the 1940s. Although nursery epidemics with enteropathogenic serotypes had decreased in recent years in the United States, the increase of infant- child day care centers has resulted in their relatively frequent occurrence. Furunculosis is most frequently caused by coagulase-positive staphylococcal infections. The public health significance of this largely relates to the hazards of skin infections in food handlers and subsequent staphylococcal toxin in the food, leading to staphylococcal intoxication food-borne disease. H. pylori has been associated with gastric ulcers, but not with duodenal ulcers. Otitis media, whether acute or with effusion, commonly results from viral infection, such as by RSV.
Various other organisms may be responsible including Streptococcu pneumoniae, H. influenzae, and others. C. perfringens, with rare exceptions, is transmitted in a meat dish prepared in bulk. Under propitious circumstances for the organism, especially on cooling of the food, bacterial multiplication can be very rapid.
Symptoms begin to occur in the affected population in about 12 hours. Epidemic typhus is a rickettsial illness. Man is the host and long-term reservoir. The vectors are body lice (P. humanus corporis). The rickettsia are not present in human excretions and cannot be transmitted by person-to-person contact.



For each of the following scenarios, select the gas exposure responsible for the signs and symptoms. A garage worker turns on the ventilation system in the winter time while testing a motor, and now complains of a headache and vertigo

  1. carbon monoxide
  2. methane
  3. hydrogen sulfide
  4. ozone
  5. sulfur dioxide

Answer(s): C

Explanation:

Carbon monoxide is an odorless, colorless, tasteless gas produced by partial combustion of tobacco and fuels. The amounts produced by cigarette smoking are not insignificant. The gas combines with hemoglobin preferentially to form carboxyhemoglobin, which makes the patient appear pink. This diminishes the oxygen-carrying capacity of the blood. The resulting anoxia is the major hazard. The onset of symptoms is insidious. Individuals exposed to carbon monoxide may not voluntarily take the action necessary to remove themselves from the toxic fumes



Select the organism associated with the following clinical findings:
A 4-year-old child in late summer fell 1 week ago, and now has a crusty, mildly erythematous wound with regional lymphadenitis.

  1. aureus
  2. beta-hemolytic Streptococcus
  3. respiratory syncytial virus (RSV)
  4. Mycoplasma pneumoniae
  5. Haemophilus pertussis
  6. Helicobacter pylori
  7. Escherichia coli
  8. Rickettsia prowazekii
  9. Giardia lamblia
  10. C. perfringens

Answer(s): B

Explanation:

Giardiasis may cause cramping and a chronic diarrheal syndrome, with malabsorption and weight loss. Its distribution is worldwide, particularly where hygienic standards are not high. It also occurs sporadically in high-risk individuals. Streptococcal pyoderma, including erysipelas and impetigo, has been demonstrated to precede acute glomerulonephritis. Even when appropriate antibiotics are given in adequate dosage and duration for these conditions, renal damage may still result. Prevention thus consists of wound care, including cleaning wounds well and removal of crust. Mycoplasma infections are particularly common in families with younger children. They are frequently imported to the family by school-aged children, leading to a low-grade fever and persisting tracheobronchitis in the parents, or more acutely, an atypical pneumonia. G. lamblia is found in up to 20% of homosexual males, and may cause chronic diarrhea, although in these patients it tends to be asymptomatic. E. coli was first reported as a cause of watery diarrhea in nurseries in the 1940s. Although nursery epidemics with enteropathogenic serotypes had decreased in recent years in the United States, the increase of infant- child day care centers has resulted in their relatively frequent occurrence. Furunculosis is most frequently caused by coagulase-positive staphylococcal infections. The public health significance of this largely relates to the hazards of skin infections in food handlers and subsequent staphylococcal toxin in the food, leading to staphylococcal intoxication food-borne disease. H. pylori has been associated with gastric ulcers, but not with duodenal ulcers. Otitis media, whether acute or with effusion, commonly results from viral infection, such as by RSV.
Various other organisms may be responsible including Streptococcu pneumoniae, H. influenzae, and others. C. perfringens, with rare exceptions, is transmitted in a meat dish prepared in bulk. Under propitious circumstances for the organism, especially on cooling of the food, bacterial multiplication can be very rapid.
Symptoms begin to occur in the affected population in about 12 hours. Epidemic typhus is a rickettsial illness. Man is the host and long-term reservoir. The vectors are body lice (P. humanus corporis). The rickettsia are not present in human excretions and cannot be transmitted by person-to-person contact.



For each of the following scenarios, select the gas exposure responsible for the signs and symptoms.

A man has been pulled unconscious from a mine. No odors are noted, but an experienced miner says there was coal damp in the mine.

  1. carbon monoxide
  2. methane
  3. hydrogen sulfide
  4. ozone
  5. sulfur dioxide

Answer(s): B

Explanation:

Methane is a colorless, odorless, flammable gas sometimes encountered in mines and wells. Methane (coal damp) is a frequent cause of death in inadequately ventilated mines and wells. It acts as an asphyxiant as well as being explosive. Miners used to take caged animals, especially birds, with them. The birds succumbed to the asphyxiants (methane and carbon dioxide) sooner than humans.



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