I85PREP
⌘ K
CIC study materials
CIC study resources

CIC (AAPC) practice questions

One question at a time. Build your CIC understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Identification of Infectious Disease Processes

Which class of microorganism is an obligate intracellular pathogen that requires a host cell for replication and lacks its own energy-generating machinery?

  1. Gram-negative bacillus
  2. Yeast
  3. Virus Correct answer.
  4. Coagulase-negative staphylococcus

Explanation

Viruses are obligate intracellular parasites that lack ribosomes and ATP-generating systems, so they must use host cell machinery to replicate. Bacteria and yeasts are free-living cells capable of independent metabolism.

Question 2Identification of Infectious Disease Processes

A 62-year-old man develops fever and productive cough three days after admission for a hip replacement. Which specimen type is most appropriate for identifying the bacterial cause of a suspected hospital-acquired pneumonia?

  1. Sputum culture Correct answer.
  2. Cerebrospinal fluid culture
  3. Wound swab of the surgical site
  4. Stool culture

Explanation

Lower respiratory infection is best evaluated with a specimen from the site of infection, so sputum (or a deeper airway specimen) is appropriate for pneumonia. Specimens from unrelated sites do not reflect the pathogen in the lung.

Question 3Identification of Infectious Disease Processes

Which term describes a microorganism's ability to cause disease?

  1. Pathogenicity Correct answer.
  2. Commensalism
  3. Colonization
  4. Antisepsis

Explanation

Pathogenicity is the capacity of an organism to produce disease, while virulence refers to the degree of that capacity. Colonization and commensalism describe carriage without disease.

Question 4Identification of Infectious Disease Processes

Which structure gives Gram-positive bacteria their ability to retain crystal violet during Gram staining?

  1. Outer membrane
  2. Flagellar sheath
  3. Lipopolysaccharide layer
  4. Thick peptidoglycan cell wall Correct answer.

Explanation

The thick peptidoglycan layer of Gram-positive cells retains the crystal violet-iodine complex after decolorization, producing a purple result. Gram-negative cells have a thin peptidoglycan layer and an outer membrane that is removed by decolorizer.

Question 5Identification of Infectious Disease Processes

Which type of culture medium contains substances that inhibit the growth of some organisms while allowing others to grow, thereby aiding isolation of a specific group of bacteria?

  1. Transport medium
  2. Differential medium
  3. Enriched medium
  4. Selective medium Correct answer.

Explanation

Selective media include inhibitors such as antibiotics, dyes, or salts that suppress unwanted flora so the target organisms can grow. Differential media instead distinguish organisms by colony appearance, and enriched media supply extra nutrients without inhibition.

Question 6Identification of Infectious Disease Processes

A patient's blood culture turns positive, and the laboratory reports a Gram-negative rod. Which statement best describes the significance of this finding?

  1. It indicates the organism is likely a fungus.
  2. It identifies the organism to species level.
  3. It provides a preliminary classification to guide empiric therapy. Correct answer.
  4. It confirms a viral bloodstream infection.

Explanation

A Gram stain result from a positive blood culture gives a rapid preliminary classification (morphology and Gram reaction) that helps guide early therapy while identification and susceptibility testing are pending. It does not provide species-level identification.

Question 7Identification of Infectious Disease Processes

Which of the following is a key difference between bacteria and fungi?

  1. Fungi are obligate intracellular organisms, whereas bacteria are extracellular.
  2. Fungi are eukaryotic with a nucleus, whereas bacteria are prokaryotic. Correct answer.
  3. Bacteria are always unicellular, whereas fungi are always multicellular.
  4. Bacteria possess chitin in their cell walls, whereas fungi possess peptidoglycan.

Explanation

Fungi are eukaryotes with a true nucleus and organelles, while bacteria are prokaryotes lacking a membrane-bound nucleus. Cell wall composition and cellularity do not follow the patterns described in the other options.

Question 8Identification of Infectious Disease Processes

Which specimen collection practice best preserves the validity of a sputum culture for suspected bacterial pneumonia?

  1. Collecting the specimen after initiating antibiotics
  2. Collecting saliva from the mouth
  3. Obtaining a deep cough specimen before antimicrobial therapy Correct answer.
  4. Storing the specimen at room temperature overnight

Explanation

A deep cough specimen collected before antibiotics reflects the lower airway flora and avoids suppression of the causative organism. Saliva is contaminated with oral flora, and delays or room-temperature storage reduce recovery of fastidious pathogens.

Question 9Identification of Infectious Disease Processes

A 45-year-old woman presents with a fluctuant, erythematous skin abscess. Which specimen is most appropriate for culture?

  1. Pus aspirated from the abscess Correct answer.
  2. A superficial swab of intact skin adjacent to the lesion
  3. Blood drawn from a peripheral vein
  4. Urine collected by clean catch

Explanation

The specimen should be obtained directly from the site of infection, so aspirated pus from the abscess yields the causative organism. Blood cultures are indicated for systemic signs, and swabbing intact adjacent skin collects colonizing flora.

Question 10Identification of Infectious Disease Processes

Which bacterial structure is primarily responsible for adherence to host cell surfaces during the initial step of colonization?

  1. Plasmid
  2. Endospore
  3. Capsule
  4. Fimbriae Correct answer.

Explanation

Fimbriae (pili) are surface appendages that mediate attachment to host epithelial cells, a critical first step in colonization. Capsules resist phagocytosis, and endospores are dormant survival structures.

Question 11Identification of Infectious Disease Processes

A laboratory reports growth of an organism that requires increased CO2 and a supplemented atmosphere to grow on primary culture. This organism is best described as which of the following?

  1. Fastidious Correct answer.
  2. Aerotolerant anaerobe
  3. Nonviable
  4. Contaminant

Explanation

Fastidious organisms have complex nutritional or atmospheric requirements and will not grow on routine media without supplementation. The need for added CO2 reflects such specialized growth requirements.

Question 12Identification of Infectious Disease Processes

Which of the following best distinguishes sterilization from disinfection?

  1. Disinfection is always performed with heat.
  2. Sterilization applies only to living tissue.
  3. Sterilization destroys all microbial life including spores, whereas disinfection reduces pathogens on inanimate objects. Correct answer.
  4. Disinfection kills all microorganisms including bacterial spores.

Explanation

Sterilization destroys or removes all microbial life, including spores, whereas disinfection reduces pathogenic organisms on inanimate surfaces and may spare spores. Antisepsis, not sterilization, applies to living tissue.

Question 13Identification of Infectious Disease Processes

A patient with neutropenia develops fever, and blood cultures grow a gram-positive coccus in clusters. Which organism is most consistent with this Gram stain morphology?

  1. Clostridium perfringens
  2. Staphylococcus aureus Correct answer.
  3. Escherichia coli
  4. Neisseria meningitidis

Explanation

Gram-positive cocci in clusters are characteristic of Staphylococcus species, and S. aureus is a common cause of bacteremia in neutropenic patients. The other organisms have different Gram stain morphology.

Question 14Identification of Infectious Disease Processes

Which of the following statements correctly describes the role of normal flora in host defense?

  1. Normal flora routinely cause invasive disease in healthy hosts.
  2. Normal flora can competitively exclude pathogens from colonizing host surfaces. Correct answer.
  3. Normal flora have no interaction with the immune system.
  4. Normal flora eliminate the need for hand hygiene.

Explanation

Indigenous microbiota occupy attachment sites and consume nutrients, providing colonization resistance against invading pathogens. They are typically nonpathogenic in their normal niche and do not replace standard infection control measures.

Question 15Identification of Infectious Disease Processes

A sputum Gram stain shows numerous squamous epithelial cells per low-power field. How should this finding be interpreted?

  1. The specimen likely reflects lower respiratory secretions.
  2. The specimen is likely contaminated with oral flora. Correct answer.
  3. The specimen should be processed for acid-fast bacilli only.
  4. The specimen is highly suitable for bacterial culture.

Explanation

Abundant squamous epithelial cells indicate saliva and oropharyngeal contamination, which reduces the value of the culture for lower respiratory pathogens. A good-quality sputum specimen has few squamous cells and many polymorphonuclear cells.

Question 16Identification of Infectious Disease Processes

Which mechanism most directly allows a bacterium to survive inside a macrophage after phagocytosis?

  1. Inhibition of phagolysosome fusion Correct answer.
  2. Production of a polysaccharide capsule that prevents ingestion
  3. Secretion of a protease that degrades antibodies
  4. Formation of a biofilm on a catheter surface

Explanation

Some intracellular pathogens survive within macrophages by preventing fusion of the phagosome with the lysosome, avoiding exposure to microbicidal contents. Capsules prevent ingestion rather than promoting intracellular survival.

Question 17Identification of Infectious Disease Processes

Which of the following best explains why a Gram stain alone cannot identify an organism to species level?

  1. Gram staining reveals only cell wall properties and morphology, which are shared by many species. Correct answer.
  2. Gram staining is specific only for fungi.
  3. Gram staining detects only anaerobic organisms.
  4. Gram staining requires living cells and cannot be performed on clinical specimens.

Explanation

Gram stain provides information on Gram reaction and cellular morphology, but many different species share the same appearance, so identification requires additional testing. It is a rapid presumptive tool rather than a definitive identifier.

Question 18Identification of Infectious Disease Processes

A newborn develops sepsis, and the laboratory isolates a gram-negative diplococcus from blood. Which organism is most consistent with this finding?

  1. Listeria monocytogenes
  2. Streptococcus pneumoniae
  3. Neisseria meningitidis Correct answer.
  4. Pseudomonas aeruginosa

Explanation

Neisseria meningitidis is a gram-negative diplococcus and a recognized cause of neonatal and childhood sepsis. The other organisms have different Gram stain morphology.

Question 19Identification of Infectious Disease Processes

Which of the following is the most important purpose of collecting a specimen before initiating antimicrobial therapy?

  1. To reduce the cost of laboratory testing
  2. To maximize recovery of the causative organism Correct answer.
  3. To avoid the need for susceptibility testing
  4. To prevent the emergence of resistant organisms

Explanation

Antimicrobials present at the time of collection can inhibit or kill the pathogen, leading to false-negative cultures. Collecting before therapy maximizes the likelihood of isolating the causative organism.

Question 20Identification of Infectious Disease Processes

A patient is suspected of having a catheter-related bloodstream infection. Which collection approach provides the most useful diagnostic information?

  1. Paired blood cultures drawn from the catheter and a peripheral vein Correct answer.
  2. A single blood culture from a peripheral vein
  3. A swab of the catheter insertion site only
  4. A urine culture collected from the indwelling catheter

Explanation

Paired cultures from the catheter and a peripheral site allow comparison of time to positivity and colony counts, supporting a catheter-related source. A single culture or site swab cannot establish the relationship between the catheter and the bloodstream infection.

Question 21Identification of Infectious Disease Processes

Which of the following best describes the difference between a bactericidal and a bacteriostatic agent as it relates to the laboratory?

  1. Bactericidal agents act only on fungi, whereas bacteriostatic agents act only on bacteria.
  2. Bactericidal and bacteriostatic agents are identical in their mechanism of action.
  3. Bactericidal drugs inhibit growth, whereas bacteriostatic drugs kill bacteria.
  4. Bactericidal drugs kill bacteria, whereas bacteriostatic drugs inhibit growth without killing. Correct answer.

Explanation

Bactericidal agents kill the organism, while bacteriostatic agents inhibit growth and require host defenses for clearance. This distinction affects interpretation of susceptibility testing and clinical response.

Question 22Identification of Infectious Disease Processes

A patient with a prosthetic joint develops chronic infection, and the laboratory reports growth of an organism only after several days of incubation on enriched media. Which factor most likely explains the delayed growth?

  1. The culture was processed at a reference laboratory
  2. The organism is a fastidious, slow-growing species requiring enriched conditions Correct answer.
  3. The organism is a strict aerobe that grows rapidly on routine media
  4. The specimen was collected after antibiotics were completed

Explanation

Slow growth on enriched media suggests a fastidious organism with complex nutritional or atmospheric requirements, common in prosthetic device infections. Rapidly growing organisms on routine media would not show this pattern.

Question 23Identification of Infectious Disease Processes

A 70-year-old man with chronic obstructive pulmonary disease has a sputum Gram stain showing numerous neutrophils and many gram-negative rods. Which interpretation is most appropriate?

  1. The finding confirms a mycobacterial infection
  2. The finding is consistent with a bacterial lower respiratory infection Correct answer.
  3. The finding indicates normal oral flora contamination
  4. The finding is consistent with a viral upper respiratory infection

Explanation

Many neutrophils with a predominant gram-negative rod morphology in a good-quality sputum specimen support a bacterial lower respiratory infection. Viral infections do not produce a predominant bacterial morphology on Gram stain.

Question 24Identification of Infectious Disease Processes

Which of the following best explains why a biofilm-forming organism on an indwelling device is difficult to eradicate with antimicrobial therapy?

  1. The biofilm matrix limits drug penetration and protects organisms from host defenses Correct answer.
  2. Biofilm organisms are always obligate intracellular pathogens
  3. Biofilm organisms lack a cell wall and are therefore resistant to all drugs
  4. Biofilm formation prevents the organism from adhering to the device

Explanation

The extracellular matrix of a biofilm impedes diffusion of antimicrobials and shields embedded organisms from phagocytes, contributing to persistent infection. Device removal is often required because drug therapy alone is insufficient.

Question 25Identification of Infectious Disease Processes

A laboratory isolates an organism from a normally sterile site that is subsequently identified as a common skin commensal. Which factor is most important in determining whether this represents true infection or contamination?

  1. The clinical context and evidence of host tissue invasion Correct answer.
  2. The number of colony types present in the culture
  3. The Gram stain reaction of the organism
  4. The organism's growth rate on enriched media

Explanation

Distinguishing infection from contamination requires correlation with clinical findings and evidence of tissue invasion, because commensals can be contaminants or true pathogens depending on the host and site. Organism characteristics alone cannot resolve this.

Question 26Identification of Infectious Disease Processes

Which of the following best describes the primary role of the capsule in pathogenic bacteria such as Streptococcus pneumoniae?

  1. It confers resistance to phagocytosis by host leukocytes. Correct answer.
  2. It provides motility by means of flagellar rotation.
  3. It serves as a site for antibiotic inactivation.
  4. It mediates attachment to host epithelial cells via pili.

Explanation

The capsule is a polysaccharide layer that inhibits opsonization and phagocytosis, enhancing virulence. Motility is provided by flagella, adherence by pili or adhesins, and antibiotic inactivation is typically enzymatic or via efflux pumps.

Question 27Identification of Infectious Disease Processes

A laboratory technologist is performing a Gram stain on a cerebrospinal fluid specimen. After staining, the organisms appear pink-red. What is the most likely explanation for this result?

  1. The organisms are gram-positive but were decolorized too long.
  2. The organisms are gram-negative because they retain the counterstain. Correct answer.
  3. The organisms are gram-variable and require a different stain.
  4. The organisms are acid-fast bacilli that resist Gram staining.

Explanation

Gram-negative bacteria have thin peptidoglycan layers that do not retain crystal violet-iodine complex and instead take up the safranin counterstain, appearing pink-red. Gram-positive organisms retain the primary stain and appear purple. Acid-fast organisms are not reliably seen on Gram stain, and gram-variable organisms are not a standard category.

Question 28Identification of Infectious Disease Processes

A patient with a suspected viral respiratory infection has a nasopharyngeal swab collected. Which of the following best explains why molecular testing is preferred over viral culture for this specimen?

  1. Viral culture is more sensitive but takes longer to yield results.
  2. Viral culture requires specific antibodies that are not commercially available.
  3. Molecular tests detect viral nucleic acid and do not require infectious virus to be present. Correct answer.
  4. Molecular tests can differentiate between latent and active viral infection.

Explanation

Molecular methods such as PCR detect viral nucleic acid even if the virus is no longer infectious or has been neutralized, offering high sensitivity. Viral culture requires viable virus and is slower and less sensitive. Molecular tests do not inherently distinguish latent from active infection, and viral culture does not rely on antibodies.

Question 29Identification of Infectious Disease Processes

A 60-year-old man with a history of recurrent Clostridioides difficile infection is treated with fecal microbiota transplantation (FMT). Which of the following best describes the mechanism by which FMT resolves the infection?

  1. Restoration of normal gut microbiota that competitively exclude C. difficile. Correct answer.
  2. Stimulation of systemic antibody production against C. difficile toxins.
  3. Introduction of bacteriophages that specifically lyse C. difficile.
  4. Direct killing of C. difficile by antimicrobial peptides present in donor stool.

Explanation

FMT works primarily by restoring a diverse gut microbiota that provides colonization resistance against C. difficile, outcompeting the pathogen for nutrients and niches. It does not rely on direct antimicrobial killing, systemic antibody stimulation, or phage therapy.

Question 30Identification of Infectious Disease Processes

A 35-year-old woman presents with fever, chills, and a new heart murmur. Blood cultures are obtained, and the laboratory reports growth of a gram-positive coccus in chains that is catalase-negative and grows in 6.5% NaCl. Which organism is most likely responsible?

  1. Streptococcus pyogenes
  2. Enterococcus faecalis Correct answer.
  3. Streptococcus pneumoniae
  4. Staphylococcus aureus

Explanation

Enterococcus faecalis is a gram-positive coccus in chains that is catalase-negative and can grow in 6.5% NaCl, distinguishing it from other streptococci. Staphylococcus aureus is catalase-positive and forms clusters; S. pneumoniae is optochin-sensitive and does not grow in 6.5% NaCl; S. pyogenes is bacitracin-sensitive and does not grow in 6.5% NaCl.

Question 31Surveillance and Epidemiologic Investigation

In an outbreak investigation, the primary purpose of a line list is to:

  1. Determine the antibiotic susceptibility of the outbreak organism
  2. Estimate the health department's staffing needs for the response
  3. Document the legal authority under which cases were reported
  4. Organize case-level data so patterns by person, place, and time can be examined Correct answer.

Explanation

A line list is a case-level table capturing identifying, demographic, clinical, and exposure variables so investigators can characterize cases and generate hypotheses. It is an analytic and descriptive tool, not a susceptibility or administrative record.

Question 32Surveillance and Epidemiologic Investigation

An epidemic curve in which cases rise rapidly and fall rapidly over a short interval, with all cases sharing a single exposure, most strongly suggests:

  1. A propagated person-to-person spread
  2. A point-source exposure Correct answer.
  3. A vector-borne seasonal pattern
  4. A continuous common-source exposure

Explanation

A sharp, narrow peak consistent with the incubation period after one exposure is characteristic of a point source. Continuous sources produce a plateau, and propagated outbreaks show successive generations of peaks.

Question 33Surveillance and Epidemiologic Investigation

The attack rate in an outbreak is best defined as:

  1. The number of deaths divided by the number of cases
  2. The number of existing cases divided by the total population at a single time
  3. The number of cases divided by the number of exposed persons only
  4. The number of new cases divided by the population at risk during a defined period Correct answer.

Explanation

Attack rate is a type of incidence proportion: new cases over the population at risk for a specified period. It measures the proportion of a population that becomes ill.

Question 34Surveillance and Epidemiologic Investigation

Which measure quantifies the strength of association between an exposure and illness in a cohort of outbreak participants?

  1. Relative risk Correct answer.
  2. Case fatality ratio
  3. Prevalence ratio from a cross-sectional survey
  4. Odds ratio from a case-control design

Explanation

In a cohort (all attendees or exposed groups followed), attack rates in exposed and unexposed can be compared directly as a relative risk. The odds ratio is the standard measure when cases and controls are sampled rather than a full cohort.

Question 35Surveillance and Epidemiologic Investigation

Investigators suspect a foodborne outbreak at a banquet and cannot enumerate all attendees. Which study design is most appropriate for testing the association between a specific food and illness?

  1. Ecological comparison of regional sales data
  2. Case-control study Correct answer.
  3. Randomized controlled trial
  4. Prospective cohort with active follow-up of all attendees

Explanation

When the population at risk cannot be fully enumerated, a case-control design comparing exposures among ill and non-ill persons is efficient. A cohort requires a defined denominator of all exposed persons.

Question 36Surveillance and Epidemiologic Investigation

During an outbreak, the term 'descriptive epidemiology' refers to characterizing cases by:

  1. Sensitivity, specificity, and predictive value
  2. Time, place, and person Correct answer.
  3. Exposure, outcome, and confounder
  4. Incidence, prevalence, and mortality

Explanation

Descriptive epidemiology organizes cases by time, place, and person to generate hypotheses. Analytic epidemiology then tests associations between exposures and outcomes.

Question 37Surveillance and Epidemiologic Investigation

A public health investigator calculates a relative risk of 4.0 with a 95% confidence interval of 1.2 to 13.0 for a suspected exposure. The most defensible interpretation is:

  1. The study has proven causation
  2. The association is not statistically significant
  3. The association is statistically significant but imprecise Correct answer.
  4. The exposure causes illness in exactly 4 of every 10 people

Explanation

The confidence interval excludes 1.0, indicating statistical significance, but the wide range (1.2 to 13.0) reflects substantial imprecision from small numbers. Significance does not establish causation.

Question 38Surveillance and Epidemiologic Investigation

The incubation period of an infectious disease is most useful in an outbreak investigation for:

  1. Determining the case fatality ratio
  2. Estimating the likely time of exposure and the period of observation Correct answer.
  3. Calculating the secondary attack rate
  4. Establishing the mode of laboratory confirmation

Explanation

Knowing the incubation period allows investigators to back-calculate the probable exposure window and set an appropriate observation period. It does not directly give fatality, secondary attack rate, or lab methods.

Question 39Surveillance and Epidemiologic Investigation

A secondary attack rate is calculated by dividing the number of cases among susceptible contacts by:

  1. The total number of cases in the outbreak
  2. The total number of susceptible contacts exposed to the primary case Correct answer.
  3. The total number of primary cases
  4. The total population of the community

Explanation

Secondary attack rate measures transmission among susceptible contacts of a primary case, so the denominator is susceptible exposed contacts. This distinguishes it from primary attack rates in the broader population.

Question 40Surveillance and Epidemiologic Investigation

Which of the following best describes the purpose of active surveillance compared with passive surveillance?

  1. Active surveillance involves health authorities seeking out cases rather than waiting for reports Correct answer.
  2. Active surveillance is conducted only during non-outbreak periods
  3. Active surveillance collects only laboratory-confirmed cases
  4. Active surveillance relies solely on death certificate review

Explanation

Active surveillance means public health staff proactively contact providers or systems to identify cases, improving completeness. Passive surveillance depends on routine reporting by providers or laboratories.

Question 41Surveillance and Epidemiologic Investigation

A notifiable disease surveillance system is best characterized as:

  1. Sentinel surveillance limited to selected clinics
  2. Passive surveillance relying on mandated reporting by clinicians and laboratories Correct answer.
  3. Syndromic surveillance based on pharmacy sales
  4. Active surveillance requiring staff to interview every household

Explanation

Notifiable disease reporting is a passive system in which providers and laboratories are legally required to report cases to health authorities. Sentinel and syndromic systems are distinct approaches.

Question 42Surveillance and Epidemiologic Investigation

In a case-control study of an outbreak, the odds ratio is used because:

  1. The exposure cannot be measured retrospectively
  2. The outcome is continuous rather than dichotomous
  3. The design does not yield incidence in exposed and unexposed groups Correct answer.
  4. Cases are selected randomly from the whole population

Explanation

Case-control studies sample on outcome, so the underlying incidence in exposed and unexposed is unknown; the odds ratio approximates the risk ratio when disease is rare. Exposures can still be measured retrospectively.

Question 43Surveillance and Epidemiologic Investigation

A cluster of pneumonia cases is reported among attendees of a convention. The first step in the investigation should be to:

  1. Begin mass prophylaxis for the entire city
  2. Publish a final case-control analysis
  3. Verify the diagnosis and confirm that the cases constitute a true excess Correct answer.
  4. Immediately close all convention venues

Explanation

Outbreak investigation begins with verifying the diagnosis and confirming that observed cases exceed expected background. Interventions and analytic studies follow once the existence of an outbreak is established.

Question 44Surveillance and Epidemiologic Investigation

A spot map is used in an outbreak investigation primarily to:

  1. Display the geographic distribution of cases by residence or exposure location Correct answer.
  2. Estimate the incubation period
  3. Compare attack rates between exposure groups
  4. Show the temporal sequence of symptom onset

Explanation

A spot map plots cases by location to reveal spatial clustering and possible common exposures. Temporal sequence is shown on an epidemic curve, and analytic comparisons require rate calculations.

Question 45Surveillance and Epidemiologic Investigation

Which of the following is the best example of a confounding variable in an outbreak study of a restaurant meal?

  1. A third food item that is served with the suspected item and independently increases illness risk Correct answer.
  2. The laboratory method used to culture the organism
  3. The number of cases identified
  4. The date the outbreak was reported

Explanation

A confounder is associated with both the exposure and the outcome and can distort the observed association. A co-served food linked to both the suspect item and illness fits this definition.

Question 46Surveillance and Epidemiologic Investigation

A surveillance system's sensitivity refers to its ability to:

  1. Correctly identify true cases among those who have the condition Correct answer.
  2. Report cases within a required time frame
  3. Detect an outbreak before it spreads
  4. Correctly identify non-cases among those without the condition

Explanation

Sensitivity is the proportion of true cases the system detects. Specificity concerns correct classification of non-cases, and timeliness is a separate attribute.

Question 47Surveillance and Epidemiologic Investigation

In an outbreak, the term 'primary case' refers to:

  1. The first case that brings the infection into a population or group Correct answer.
  2. Any case that occurs after the index case
  3. A case with the most severe symptoms
  4. A case identified through laboratory testing only

Explanation

A primary case is the person who introduces infection into a population or group; subsequent cases arising from that introduction are secondary. Severity and testing method do not define primary status.

Question 48Surveillance and Epidemiologic Investigation

An investigator wants to assess whether a water source is associated with illness using a cohort of village residents who use either a well or a river. The appropriate comparison is:

  1. Attack rate among well users versus attack rate among river users Correct answer.
  2. Number of well users versus number of river users
  3. Total cases in the village versus cases in neighboring villages
  4. Prevalence of illness at one point in time among all residents

Explanation

Comparing attack rates between exposure groups (well versus river) estimates the association between water source and illness. Comparing group sizes or unrelated populations does not test the exposure-outcome link.

Question 49Surveillance and Epidemiologic Investigation

The main advantage of syndromic surveillance is that it:

  1. Eliminates the need for case investigation
  2. Measures case fatality accurately
  3. Can detect increases in illness before laboratory confirmation is available Correct answer.
  4. Provides definitive pathogen identification

Explanation

Syndromic surveillance uses pre-diagnostic indicators such as symptom patterns or sales data to detect increases early. It lacks pathogen specificity and does not replace confirmatory testing or investigation.

Question 50Surveillance and Epidemiologic Investigation

During an outbreak of hepatitis A linked to a restaurant, investigators find that 60% of ill persons ate a specific dessert compared with 20% of well persons. Which analytic step best follows?

  1. Declare the dessert the cause without further analysis
  2. Report only the number of ill persons who ate the dessert
  3. Calculate an odds ratio and test its statistical significance Correct answer.
  4. Stop the investigation because a difference was observed

Explanation

Observed differences in exposure between ill and well persons should be quantified with an odds ratio and evaluated for statistical significance and bias. Causation requires further criteria and control measures.