Infectious disease screening US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Infectious disease screening. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Infectious disease screening US Medical PG Question 1: A 24-year-old gravida 2 para 0 presents to her physician at 15 weeks gestation to discuss the results of recent screening tests. She has no complaints and the current pregnancy has been uncomplicated. Her previous pregnancy terminated with spontaneous abortion in the first trimester. Her immunizations are up to date. Her vital signs are as follows: blood pressure 110/60 mm Hg, heart rate 78/min, respiratory rate 14/min, and temperature 36.8℃ (98.2℉). The physical examination is within normal limits. The laboratory screening tests show the following results:
HBsAg negative
HBcAg negative
Anti-HBsAg positive
HIV 1/2 AB negative
VDRL positive
What is the proper next step in the management of this patient?
- A. Full serum panel for HBV
- B. PCR for HBV DNA
- C. HBV vaccination
- D. Prescription of benzylpenicillin
- E. T. pallidum hemagglutination assay (Correct Answer)
Infectious disease screening Explanation: ***T. pallidum hemagglutination assay***
- A positive **Venereal Disease Research Laboratory (VDRL)** test indicates potential exposure to syphilis, but it is a **non-treponemal test** and can yield false positives.
- A **treponemal test** such as the *T. pallidum* hemagglutination assay (TPHA) or fluorescent treponemal antibody-absorbed (FTA-ABS) is required to confirm the diagnosis of syphilis.
*Full serum panel for HBV*
- The **hepatitis B surface antigen (HBsAg)** is negative, and **anti-HBsAg (HBsAb)** is positive, indicating either prior vaccination or resolved infection with immunity.
- This patient does not have active hepatitis B infection, so a full serum panel for HBV is not necessary.
*PCR for HBV DNA*
- Similar to the above, the serological markers indicate immunity to HBV, not active infection.
- **PCR for HBV DNA** would only be indicated if there were signs of active infection or **occult HBV**.
*HBV vaccination*
- The patient already has **protective antibodies (anti-HBsAg)** against Hepatitis B, indicating immunity.
- Vaccination would be redundant as she is already immune.
*Prescription of benzylpenicillin*
- While **benzylpenicillin** is the treatment for syphilis, a definitive diagnosis has not yet been made.
- Confirmation with a **treponemal test** is crucial before initiating treatment to avoid unnecessary antibiotic exposure.
Infectious disease screening US Medical PG Question 2: A 24-year-old man comes to the physician for a routine health maintenance examination. He feels well. He has type 1 diabetes mellitus. His only medication is insulin. He immigrated from Nepal 2 weeks ago . He lives in a shelter. He has smoked one pack of cigarettes daily for the past 5 years. He has not received any routine childhood vaccinations. The patient appears healthy and well nourished. He is 172 cm (5 ft 8 in) tall and weighs 68 kg (150 lb); BMI is 23 kg/m2. His temperature is 36.8°C (98.2°F), pulse is 72/min, and blood pressure is 123/82 mm Hg. Examination shows a healed scar over his right femur. The remainder of the examination shows no abnormalities. A purified protein derivative (PPD) skin test is performed. Three days later, an induration of 13 mm is noted. Which of the following is the most appropriate initial step in the management of this patient?
- A. Administer isoniazid for 9 months
- B. Collect sputum sample for culture
- C. Perform interferon-γ release assay
- D. Obtain a chest x-ray (Correct Answer)
- E. Perform PCR of the sputum
Infectious disease screening Explanation: ***Obtain a chest x-ray***
- A **positive PPD test** (13 mm induration in a patient with risk factors) indicates possible **latent tuberculosis infection (LTBI)**, but before initiating treatment, it's crucial to rule out **active tuberculosis (TB)**.
- A chest x-ray is the initial step to screen for signs of active disease, such as **infiltrates, cavitations**, or **lymphadenopathy**, which would necessitate a different treatment regimen than LTBI.
*Administer isoniazid for 9 months*
- This is a standard treatment for **LTBI**, but it should only be initiated after **active TB has been ruled out**.
- Treating active TB with LTBI monotherapy would be inadequate and could lead to **drug resistance**.
*Collect sputum sample for culture*
- **Sputum culture** is essential for diagnosing active pulmonary TB and for **drug susceptibility testing**, but it's typically performed *after* a chest x-ray suggests active disease.
- In a patient with a positive PPD and no symptoms, starting with sputum cultures without imaging is not the most appropriate first step.
*Perform interferon-γ release assay*
- **Interferon-γ release assays (IGRAs)**, such as QuantiFERON-TB Gold or T-Spot.TB, are alternative tests for detecting **M. tuberculosis infection**.
- While IGRAs can be used in place of or in conjunction with PPD, they also do not differentiate between latent and active infection, so a chest x-ray would still be required.
*Perform PCR of the sputum*
- **PCR (nucleic acid amplification test)** of sputum rapidly detects *M. tuberculosis* DNA and is a valuable tool for diagnosing **active TB**, especially in cases where rapid results are needed.
- However, like sputum culture, it is usually reserved for situations where there is a strong suspicion of active disease based on clinical symptoms or imaging findings.
Infectious disease screening US Medical PG Question 3: A 27-year-old man interested in pre-exposure therapy for HIV (PrEP) is being evaluated to qualify for a PrEP study. In order to qualify, patients must be HIV- and hepatitis B- and C-negative. Any other sexually transmitted infections require treatment prior to initiation of PrEP. The medical history is positive for a prior syphilis infection and bipolar affective disorder, for which he takes lithium. On his next visit, the liver and renal enzymes are within normal ranges. HIV and hepatitis B and C tests are negative. Which of the following about the HIV test is true?
- A. It is a quantitative test used for screening purposes.
- B. It is a qualitative test used for screening purposes. (Correct Answer)
- C. A secondary reagent is needed to interpret the results.
- D. A known antigen binds directly to the patient's serum.
- E. An unknown antigen binds to the known serum.
Infectious disease screening Explanation: ***It is a qualitative test used for screening purposes.***
- **HIV screening tests** (e.g., 4th generation antibody/antigen combination assays) are typically **qualitative**, meaning they detect the presence or absence of HIV markers, not their exact amount.
- These tests are primarily used for broad **screening** of populations to identify potential cases of HIV infection.
*It is a quantitative test used for screening purposes.*
- **Quantitative tests** for HIV, such as viral load tests, measure the amount of virus in the blood and are typically used for monitoring disease progression or treatment effectiveness, not for initial screening.
- Screening tests are designed for high sensitivity to detect infection, even with low viral loads or early antibody responses, making a quantitative measurement less relevant for initial screening.
*A secondary reagent is needed to interpret the results.*
- While some complex immunoassays might involve multiple steps, modern **HIV screening tests** often use advanced technologies that directly yield results, making a separate secondary reagent for interpretation generally unnecessary.
- The results are typically indicated by a color change or a signal detected by an instrument, without requiring an additional interpretive reagent.
*A known antigen binds directly to the patient's serum.*
- **HIV antibody tests** detect **antibodies** produced by the patient's immune system in response to HIV infection.
- In such tests, **known HIV antigens** (from the test kit) bind to **HIV-specific antibodies present in the patient's serum**, not to serum components directly.
- This option is incorrect because it omits the critical role of antibodies as the target molecules being detected.
*An unknown antigen binds to the known serum.*
- This statement describes a different type of immunological assay where an unknown antigen is being identified using a known antibody, which is contrary to how **HIV screening tests** for infection are typically structured.
- **HIV screening tests** use known components (e.g., HIV antigens or antibodies) in the test kit to detect unknown components (e.g., HIV antibodies or viral antigens) in the patient's sample.
Infectious disease screening US Medical PG Question 4: A 35-year-old man with no known past medical history presents to his physician because he is applying for a job as a healthcare worker, which requires screening for the hepatitis B virus (HBV). The patient states that he is in good health and denies any symptoms. His vital signs and physical exam are unremarkable. Labs are drawn, and the patient's HBV serology shows the following:
HBsAg: positive
anti-HBsAg antibody: negative
anti-HBcAg IgM: negative
anti-HBcAg IgG: positive
HBeAg: negative
anti-HBeAg antibody: positive
Which of the following best describes this patient's results?
- A. Immune due to previous infection
- B. Chronically infected, low infectivity (Correct Answer)
- C. Immune due to previous vaccination
- D. Acutely infected
- E. Chronically infected, high infectivity
Infectious disease screening Explanation: ***Chronically infected, low infectivity***
- The presence of **HBsAg positive** for more than 6 months indicates **chronic HBV infection**. The presence of **anti-HBeAg antibody** and **negative HBeAg** suggests **low viral replication activity** and thus low infectivity.
- **HBeAg negativity** along with positivity for **HBV DNA** (if tested, though not provided here) would further differentiate this state as **"HBeAg-negative chronic hepatitis B,"** which typically implies lower, but still present, infectivity compared to HBeAg-positive chronic infection.
*Immune due to previous infection*
- Immunity due to previous infection is characterized by **negative HBsAg** and **positive anti-HBsAg antibody**, along with **positive anti-HBcAg IgG**.
- This patient, however, is **HBsAg positive** and **anti-HBsAg antibody negative**, ruling out resolved infection.
*Immune due to previous vaccination*
- Immunity due to vaccination is characterized by **negative HBsAg**, **positive anti-HBsAg antibody**, and **negative anti-HBcAg antibody** (both IgM and IgG).
- This patient has **positive HBsAg** and **positive anti-HBcAg IgG**, indicating either current or past infection, not vaccination-induced immunity.
*Acutely infected*
- **Acute infection** is characterized by **positive HBsAg**, **negative anti-HBsAg antibody**, and typically **positive anti-HBcAg IgM**.
- This patient has **negative anti-HBcAg IgM**, which makes acute infection unlikely, as IgM antibodies are present early in acute infection.
*Chronically infected, high infectivity*
- **High infectivity** in chronic HBV infection is typically indicated by **positive HBsAg** and **positive HBeAg**, often with high levels of HBV DNA.
- This patient is **HBeAg negative** and **anti-HBeAg antibody positive**, indicating a lower level of viral replication and thus lower infectivity.
Infectious disease screening US Medical PG Question 5: An endocervical swab is performed and nucleic acid amplification testing via polymerase chain reaction is conducted. It is positive for Chlamydia trachomatis and negative for Neisseria gonorrhoeae. Which of the following is the most appropriate pharmacotherapy?
- A. Oral azithromycin (Correct Answer)
- B. Intramuscular ceftriaxone plus oral azithromycin
- C. Oral doxycycline
- D. Intramuscular ceftriaxone
- E. Intravenous cefoxitin plus oral doxycycline
Infectious disease screening Explanation: ***Oral azithromycin***
- A single 1-gram oral dose of **azithromycin** is a highly effective and convenient first-line treatment for uncomplicated **Chlamydia trachomatis** infections.
- Its long half-life allows for once-daily dosing, improving patient adherence.
*Intramuscular ceftriaxone plus oral azithromycin*
- This combination therapy is primarily used for suspected or confirmed **gonorrhea** and chlamydia coinfection, particularly if N. gonorrhoeae cannot be ruled out.
- Since **Neisseria gonorrhoeae** was explicitly negative, the ceftriaxone component is unnecessary.
*Oral doxycycline*
- **Doxycycline** (100 mg twice daily for 7 days) is an alternative first-line treatment for **Chlamydia trachomatis** infections and is highly effective.
- However, azithromycin is often preferred for its single-dose regimen which can improve treatment adherence, especially in asymptomatic patients.
*Intramuscular ceftriaxone*
- **Ceftriaxone** is the primary treatment for **Neisseria gonorrhoeae** infections.
- As the test for **N. gonorrhoeae** was negative, this treatment is not indicated for the current patient's diagnosis.
*Intravenous cefoxitin plus oral doxycycline*
- This regimen is typically reserved for more severe infections, such as **pelvic inflammatory disease (PID)**, often requiring hospitalization, which is not indicated by the simple positive chlamydia swab.
- Administering **IV cefoxitin** is an escalation beyond what is necessary for uncomplicated chlamydial cervicitis.
Infectious disease screening US Medical PG Question 6: A 34-year-old man comes to the physician for a routine health maintenance examination. He was diagnosed with HIV 8 years ago. He is currently receiving triple antiretroviral therapy. He is sexually active and uses condoms consistently. He is planning a trip to Thailand with his partner to celebrate his 35th birthday in 6 weeks. His last tetanus and diphtheria booster was given 4 years ago. He received three vaccinations against hepatitis B 5 years ago. He had chickenpox as a child. Other immunization records are unknown. Vital signs are within normal limits. Cardiopulmonary examination shows no abnormalities. Leukocyte count shows 8,700/mm3, and CD4+ T-lymphocyte count is 480 cells/mm3 (Normal ≥ 500); anti-HBs is 150 mIU/mL. Which of the following recommendations is most appropriate at this time?
- A. Yellow fever vaccine
- B. Hepatitis B vaccine
- C. Tetanus, diphtheria, pertussis vaccine (Tdap)
- D. Measles, mumps, rubella vaccine
- E. No vaccination (Correct Answer)
Infectious disease screening Explanation: ***Correct: No vaccination***
- Given the patient's current immunization status and clinical scenario, **none of the listed vaccines are indicated at this time**.
- His CD4+ count of 480 cells/mm³ indicates relatively preserved immune function on effective antiretroviral therapy.
- His **anti-HBs level of 150 mIU/mL** demonstrates **adequate hepatitis B immunity** (protective level ≥10 mIU/mL).
- His **tetanus-diphtheria booster was given 4 years ago**, and routine boosters are recommended every **10 years**, so he is not due for another 6 years.
*Incorrect: Yellow fever vaccine*
- **Thailand is not a yellow fever endemic country**, so yellow fever vaccination is **not required or recommended** for travel there.
- Yellow fever vaccine is a **live attenuated vaccine** that can be given to HIV-positive patients with **CD4+ counts ≥200 cells/mm³** when travel to endemic areas (parts of Africa and South America) is necessary.
- Since the patient has a CD4+ count of 480 and Thailand doesn't require this vaccine, this is not applicable.
*Incorrect: Hepatitis B vaccine*
- The patient's **anti-HBs level of 150 mIU/mL** indicates **adequate protective immunity** against hepatitis B.
- A level ≥10 mIU/mL is considered protective, so **no booster is needed**.
*Incorrect: Tetanus, diphtheria, pertussis vaccine (Tdap)*
- **Tetanus-diphtheria boosters are recommended every 10 years**.
- The patient received his last booster **4 years ago**, so he is **not due** for another booster at this time.
- There is no specific indication for **pertussis vaccination** (e.g., pregnancy, close contact with infants).
*Incorrect: Measles, mumps, rubella vaccine*
- **MMR is a live attenuated vaccine** that is **contraindicated** in HIV-positive individuals with **CD4+ counts <200 cells/mm³**.
- While this patient's CD4+ count is 480, MMR should only be given to HIV patients if they lack immunity and have CD4 ≥200.
- There is **no documented need** for MMR based on the clinical scenario provided, and his immunity status to these infections is unknown.
- Without evidence of susceptibility or specific exposure risk, vaccination is not indicated.
Infectious disease screening US Medical PG Question 7: A 36-year-old man comes to the physician because of a 2-week history of productive cough, weight loss, and intermittent fever. He recently returned from a 6-month medical deployment to Indonesia. He appears tired. Physical examination shows nontender, enlarged, palpable cervical lymph nodes. An x-ray of the chest shows right-sided hilar lymphadenopathy. A sputum smear shows acid-fast bacilli. A diagnosis of pulmonary tuberculosis is made from PCR testing of the sputum. The patient requests that the physician does not inform anyone of this diagnosis because he is worried about losing his job. Which of the following is the most appropriate initial action by the physician?
- A. Request the patient's permission to discuss the diagnosis with an infectious disease specialist
- B. Assure the patient that his diagnosis will remain confidential
- C. Confirm the diagnosis with a sputum culture
- D. Notify all of the patient's household contacts of the diagnosis
- E. Inform the local public health department of the diagnosis (Correct Answer)
Infectious disease screening Explanation: ***Inform the local public health department of the diagnosis***
- **Tuberculosis** is a **reportable disease** to public health authorities due to its significant public health implications, including the risk of transmission.
- Physicians have a **legal and ethical obligation** to report such diagnoses to protect the community, even against a patient's wishes for secrecy.
*Request the patient's permission to discuss the diagnosis with an infectious disease specialist*
- While consulting an infectious disease specialist is often beneficial for managing TB, the immediate and most appropriate initial action is related to **public health notification**.
- Delaying notification to seek patient permission first would **compromise public health safety** regarding a reportable disease.
*Assure the patient that his diagnosis will remain confidential*
- This assurance would be **misleading and unethical** because TB is a reportable condition, meaning its confidentiality is necessarily breached for public health purposes.
- Physicians are bound by law to report communicable diseases, which supersedes general confidentiality in this specific context.
*Confirm the diagnosis with a sputum culture*
- The diagnosis of pulmonary tuberculosis has already been established by a **sputum smear showing acid-fast bacilli** and **PCR testing**, which are highly reliable.
- While a sputum culture provides drug susceptibility information, it is not the *initial* most appropriate action regarding the patient's stated concerns about confidentiality in the context of a reportable disease.
*Notify all of the patient's household contacts of the diagnosis*
- While contact tracing is an important part of TB control, it is typically initiated and managed by the **public health department** after notification.
- The physician's primary responsibility is to notify the health department, who then assumes the role of **contact investigation** and management.
Infectious disease screening US Medical PG Question 8: A pharmaceutical corporation is developing a research study to evaluate a novel blood test to screen for breast cancer. They enrolled 800 patients in the study, half of which have breast cancer. The remaining enrolled patients are age-matched controls who do not have the disease. Of those in the diseased arm, 330 are found positive for the test. Of the patients in the control arm, only 30 are found positive. What is this test’s sensitivity?
- A. 330 / (330 + 30)
- B. 330 / (330 + 70) (Correct Answer)
- C. 370 / (30 + 370)
- D. 370 / (70 + 370)
- E. 330 / (400 + 400)
Infectious disease screening Explanation: ***330 / (330 + 70)***
- **Sensitivity** measures the proportion of actual **positives** that are correctly identified as such.
- In this study, there are **400 diseased patients** (half of 800). Of these, 330 tested positive (true positives), meaning 70 tested negative (false negatives). So sensitivity is **330 / (330 + 70)**.
*330 / (330 + 30)*
- This calculation represents the **positive predictive value**, which is the probability that subjects with a positive screening test truly have the disease. It uses **true positives / (true positives + false positives)**.
- It does not correctly calculate **sensitivity**, which requires knowing the total number of diseased individuals.
*370 / (30 + 370)*
- This expression is attempting to calculate **specificity**, which is the proportion of actual negatives that are correctly identified. It would be **true negatives / (true negatives + false positives)**.
- However, the numbers used are incorrect for specificity in this context given the data provided.
*370 / (70 + 370)*
- This formula is an incorrect combination of values and does not represent any standard epidemiological measure like **sensitivity** or **specificity**.
- It is attempting to combine false negatives (70) and true negatives (370 from control arm) in a non-standard way.
*330 / (400 + 400)*
- This calculation attempts to divide true positives by the total study population (800 patients).
- This metric represents the **prevalence of true positives within the entire study cohort**, not the test's **sensitivity**.
Infectious disease screening US Medical PG Question 9: A 28-year-old asymptomatic pregnant woman at 12 weeks gestation presents for prenatal care. She has no personal or family history of diabetes. Her BMI is 32 kg/m². She had a random glucose of 118 mg/dL at her first visit. She asks about gestational diabetes screening. Considering her risk factors and current pregnancy, what is the most appropriate screening approach?
- A. Perform 3-hour oral glucose tolerance test at 16 weeks
- B. Diagnose gestational diabetes based on random glucose and begin treatment
- C. Perform 1-hour glucose challenge test now
- D. Perform fasting glucose and hemoglobin A1c now to assess for preexisting diabetes (Correct Answer)
- E. Defer screening until 24-28 weeks gestation per routine protocol
Infectious disease screening Explanation: ***Perform fasting glucose and hemoglobin A1c now to assess for preexisting diabetes***
- A **BMI ≥ 30 kg/m²** is a major risk factor necessitating early screening at the first prenatal visit to identify **pre-existing (overture) diabetes**.
- Identifying hyperglycemia early in pregnancy allows for immediate management to reduce the risk of **congenital anomalies** associated with pre-gestational diabetes.
*Perform 1-hour glucose challenge test now*
- While the **1-hour GCT** is a valid tool for early screening, standard biomarkers like **fasting plasma glucose** or **HbA1c** are also appropriate for detecting overt diabetes at the initial visit.
- The goal in the first trimester for high-risk patients is often to rule out **Type 2 Diabetes mellitus** that existed prior to pregnancy.
*Defer screening until 24-28 weeks gestation per routine protocol*
- Routine screening at **24-28 weeks** is reserved for women without significant risk factors; this patient's **obesity** mandates earlier evaluation.
- Delayed screening in obese patients may miss a window for intensive **glycemic control** during critical fetal organogenesis.
*Diagnose gestational diabetes based on random glucose and begin treatment*
- A **random glucose of 118 mg/dL** is within the normal range and is not diagnostic of either GDM (which requires >200 mg/dL with symptoms) or overt diabetes.
- Diagnosis requires structured testing such as an **HbA1c ≥ 6.5%**, fasting glucose ≥ 126 mg/dL, or a formal **oral glucose tolerance test (OGTT)**.
*Perform 3-hour oral glucose tolerance test at 16 weeks*
- The **3-hour OGTT** is typically the second step of a two-step screening process and is not indicated as an initial screening tool at 16 weeks.
- High-risk patients should be screened as soon as possible, often at the **first prenatal visit** (12 weeks in this case), rather than waiting until the second trimester.
Infectious disease screening US Medical PG Question 10: A 66-year-old man underwent screening colonoscopy which revealed a 1.2 cm tubular adenoma with low-grade dysplasia in the sigmoid colon that was completely removed. He has no family history of colorectal cancer. His colonoscopy 8 years ago was normal. He asks about surveillance recommendations. Considering current guidelines and competing risks, what is the most appropriate surveillance interval?
- A. Annual fecal immunochemical testing
- B. Repeat colonoscopy in 3 years
- C. Repeat colonoscopy in 10 years
- D. Repeat colonoscopy in 1 year
- E. Repeat colonoscopy in 5-10 years (Correct Answer)
Infectious disease screening Explanation: ***Repeat colonoscopy in 5-10 years***
- According to the **USMSTF 2020 guidelines**, patients with **1 to 2 small (<10 mm) tubular adenomas** should have a surveillance colonoscopy in **7-10 years**; however, for a single adenoma **≥ 10 mm** (like this 1.2 cm lesion) with low-grade dysplasia, the recommended interval is **5-10 years**.
- This recommendation balances the slightly higher risk of a **larger lesion** against the **low-grade pathology** and the patient's age and overall risk profile.
*Repeat colonoscopy in 10 years*
- A strictly **10-year interval** is reserved for patients with a **normal colonoscopy** or those with only **distal hyperplastic polyps**.
- While 10 years is the upper limit of the recommended range, the presence of a **1.2 cm adenoma** requires a surveillance designation rather than a standard screening interval.
*Repeat colonoscopy in 3 years*
- The **3-year interval** is indicated for **high-risk findings** such as **≥3 adenomas**, adenomas with **villous histology**, or those with **high-grade dysplasia**.
- This patient only had a single lesion with **low-grade dysplasia**, making 3-year surveillance an over-utilization of resources.
*Repeat colonoscopy in 1 year*
- A **1-year interval** is generally only indicated for cases of **incomplete resection**, piece-meal removal of large sessile polyps, or **inadequate bowel preparation**.
- It is not appropriate for a **completely removed** 1.2 cm tubular adenoma.
*Annual fecal immunochemical testing*
- **Fecal immunochemical testing (FIT)** is a primary **screening modality**, not a surveillance tool for patients who have already been diagnosed with adenomas via colonoscopy.
- Once an adenoma is identified, the patient enters a **colonoscopy-based surveillance** program to directly monitor for recurrent or advancing lesions.
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