Within 2 to 6 hours of a wedding lunch in a village, 64 of 150 guests develop vomiting and abdominal cramps. The epidemic curve rises sharply to a single peak and falls, with no new cases after the next day. What type of epidemic is this?

Continuous common-source epidemic

Under IDSP, a sudden rise in cases of fever with rash is flagged from a block. Which team is primarily responsible for investigating the outbreak in the field and starting control measures?

The district Rapid Response Team

The village health sanitation committee

The national programme officer in Delhi

The private practitioners of the block

Outbreak investigation and surveillance (IDSP, IHIP)

23 NEET-PG practice questions on Outbreak investigation and surveillance (IDSP, IHIP), part of Community Medicine. The first 23 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Easy
Within 2 to 6 hours of a wedding lunch in a village, 64 of 150 guests develop vomiting and abdominal cramps. The epidemic curve rises sharply to a single peak and falls, with no new cases after the next day. What type of epidemic is this?
1. AContinuous common-source epidemic
2. BSlow (modern) epidemic
3. CPropagated epidemic
4. DPoint-source epidemic
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Answer: D · Point-source epidemic
A single exposure to a common source produces cases that all fall within one incubation period, giving a sharp rise, a single peak and a quick fall. The short incubation of 2-6 hours suggests a preformed toxin such as that of Staphylococcus aureus. A propagated epidemic spreads from person to person and shows successive, wider peaks over several incubation periods. A continuous common source, such as a contaminated well, gives a plateau that lasts until the source is removed.
- A: A continuing source gives a plateau, not one sharp peak.
- B: Slow epidemics such as heart disease build over years.
- C: Person-to-person spread gives successive peaks over weeks.
Question 2 · Medium
Under IDSP, a sudden rise in cases of fever with rash is flagged from a block. Which team is primarily responsible for investigating the outbreak in the field and starting control measures?
1. AThe district Rapid Response Team
2. BThe village health sanitation committee
3. CThe national programme officer in Delhi
4. DThe private practitioners of the block
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Answer: A · The district Rapid Response Team
IDSP sets up Rapid Response Teams at district and state level, usually with an epidemiologist, a clinician and a microbiologist, to investigate outbreaks quickly, collect samples, and begin containment. The district surveillance unit receives the alert and sends the team. Village committees and private practitioners help with reporting and community action but do not lead investigations. The national level supports states when outbreaks are large or unusual.
- B: Village committees support action locally but do not investigate outbreaks.
- C: The national level supports, but the district team responds first.
- D: Private practitioners report cases but do not lead investigations.
Question 3 · Hard
All 100 guests at a village wedding are traced after an outbreak of food poisoning. Of the 60 who ate the chicken curry, 45 fell ill; of the 40 who did not, 4 fell ill. Which measure of association should be calculated, and what is its value?
1. ARelative risk, 7.5
2. BOdds ratio, 27
3. COdds ratio, 7.5
4. DRelative risk, 11.3
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Answer: A · Relative risk, 7.5
Because every person at risk is known, the investigation is a retrospective cohort study and attack rates can be calculated directly. Attack rate among those who ate the curry = 45/60 = 75%, and among those who did not = 4/40 = 10%, so the relative risk is 75/10 = 7.5. The odds ratio, (45 x 36)/(15 x 4) = 27, overstates the risk when the illness is common, as here. The odds ratio is used when only a sample of cases and controls is studied.
- B: The odds ratio is for case-control studies and overstates risk when the illness is common.
- C: 7.5 is the relative risk, not the odds ratio.
- D: 11.3 is cases among eaters divided by cases among non-eaters, ignoring the group sizes.
Question 4 · Hard
After a community lunch in a village, 30 people develop abdominal cramps and watery diarrhoea 8 to 16 hours later; vomiting and fever are uncommon, and all recover within a day. The meal included a large pot of mutton curry cooked the previous evening and left to cool slowly overnight. What is the most likely causative organism?
1. ASalmonella Typhimurium
2. BClostridium perfringens
3. CBacillus cereus, emetic type
4. DStaphylococcus aureus
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Answer: B · Clostridium perfringens
Clostridium perfringens type A food poisoning typically has an incubation period of about 8-16 hours, with cramps and watery diarrhoea, little vomiting, no fever and recovery within 24 hours. Its spores survive cooking, and germinate when large volumes of meat dishes cool slowly; the vegetative cells then form an enterotoxin in the gut. Staphylococcal and emetic Bacillus cereus poisoning start within 1-6 hours with prominent vomiting, from a preformed toxin. Prevention is rapid cooling and thorough reheating of cooked food.
- A: Salmonella usually causes fever and illness lasting several days.
- C: The emetic B. cereus toxin acts within 1-6 hours with vomiting.
- D: S. aureus toxin causes vomiting within 1-6 hours.
Question 5 · Medium
During a measles outbreak in a tribal hamlet, 8 households each have one primary case. These households contain 50 other children, of whom 20 had measles in the past. Within 7 to 18 days of the primary cases, 9 more children in these households fall ill with measles. What is the secondary attack rate?
1. A29%
2. B45%
3. C30%
4. D18%
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Answer: C · 30%
The secondary attack rate is the number of secondary cases among contacts within the incubation period, divided by the number of susceptible contacts. Primary cases are excluded from both numerator and denominator, and immune contacts are excluded from the denominator. Susceptible contacts are 50 - 20 = 30, so the SAR = 9/30 = 30%. It measures the infectiousness of the disease and the effect of control measures within households.
- A: 29% wrongly adds the 8 primary cases to numerator and denominator.
- B: 45% divides by the 20 immune children instead of the susceptibles.
- D: 18% uses all 50 contacts, including the 20 immune children.
Question 6 · Medium
After a temple feast attended by 150 people, 87 develop diarrhoea. The investigating team records: chicken biryani, 120 ate (84 ill) and 30 did not (3 ill); raita, 100 ate (60 ill) and 50 did not (27 ill); sweet, 90 ate (50 ill) and 60 did not (37 ill); fruit salad, 40 ate (24 ill) and 110 did not (63 ill). Which food is most likely the vehicle?
1. ARaita
2. BChicken biryani
3. CFruit salad
4. DSweet
Answer and explanation in LearnFree account
Question 7 · Hard
In an urban slum, 85 cases of acute watery diarrhoea with severe dehydration appear over 5 days, and Vibrio cholerae O1 is isolated from stool. Cases are spread over three lanes that share one municipal pipeline, and residual chlorine at the taps is nil. Rehydration centres are already running. What is the most important immediate public health measure?
1. AMass doxycycline prophylaxis for all residents
2. BRestore chlorination and repair the leaking pipeline
3. CClose all street food stalls in the area
4. DOral cholera vaccine for all as the first step
Answer and explanation in LearnFree account
Question 8 · Medium
A PHC reports 14 cases of acute diarrhoea in one week from a village where, in the same week of each of the past three years, the PHC recorded about 5 cases. The district surveillance officer compares these figures. What is the purpose of this comparison?
1. AIdentifying the vehicle of infection
2. BCalculating the case fatality rate
3. CVerifying the clinical diagnosis
4. DConfirming that an outbreak really exists
Answer and explanation in LearnFree account
Question 9 · Medium
A district surveillance officer explains to new medical officers how outbreak data now reach the state and the Centre through the Integrated Health Information Platform (IHIP). What does IHIP add to IDSP surveillance?
1. ANear real-time digital, geo-tagged case reporting
2. BReporting from private laboratories only
3. CMonthly paper reports sent by post
4. DSurveillance of non-communicable diseases only
Answer and explanation in LearnFree account
Question 10 · Medium
A district team writing a case definition for an outbreak of gastroenteritis after a college fest considers including: 1. Clinical criteria, such as three or more loose stools in 24 hours. 2. A time restriction, such as onset between two given dates. 3. A place or person restriction, such as students and staff of the college. 4. Having eaten at a particular stall suspected as the source. Which should be in the case definition?
1. A3 and 4 only
2. B1 and 3 only
3. C1, 2 and 4 only
4. D1, 2 and 3 only
Answer and explanation in LearnFree account
Question 11 · Medium
In a town, cases of hepatitis E start rising 4 weeks after a sewage line begins leaking into the drinking-water pipeline. New cases keep appearing at a roughly steady level for 8 weeks, and fall only after the leak is repaired. What shape will the epidemic curve show?
1. AA slow rise over several years
2. BA single sharp peak, then a rapid fall
3. CA plateau lasting while exposure continues
4. DSuccessive peaks one incubation apart
Answer and explanation in LearnFree account
Question 12 · Medium
During a diphtheria outbreak in an urban slum, the district team learns that the illness first came to official notice when a 7-year-old was admitted to the district hospital. Field inquiry later finds that his cousin had a sore throat with a membrane a week earlier and was never seen by a doctor. What is the 7-year-old called in the investigation?
1. AThe index case
2. BA secondary case
3. CThe primary case
4. DA carrier
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Question 13 · Easy
In a residential school, cases of hepatitis A occur in three waves over four months, each wave larger than the last and the peaks separated by about four weeks; the water supply has been tested and found safe. What type of epidemic is this?
1. APoint-source epidemic
2. BPropagated epidemic
3. CContinuous common-source epidemic
4. DSeasonal endemic variation
Answer and explanation in LearnFree account
Question 14 · Medium
During a typhoid outbreak in a town, the team selects 40 cases and 80 healthy neighbourhood controls. Eating pani puri from one street vendor is reported by 30 cases and 20 controls. What is the odds ratio for this exposure?
1. A3
2. B9
3. C0.11
4. D1.5
Answer and explanation in LearnFree account
Question 15 · Medium
During an outbreak of acute watery diarrhoea in a town ward, the investigating officer marks the house of each case on a ward map and finds that the cases cluster around one public standpost, while houses using a different supply are spared. Which step of descriptive epidemiology does this represent?
1. AAnalysis by person, by age and sex
2. BAnalysis by place, using a spot map
3. CAnalysis by time, using an epidemic curve
4. DTesting a hypothesis by case-control study
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Question 16 · Hard
In a girls' hostel, 26 students develop hepatitis A, with onset of jaundice from 10 August to 30 August; all appear to come from one common exposure. The incubation period of hepatitis A is taken as 15-50 days. Events in the hostel were: a picnic on 2 July, a feast on 18 July, a water-tank cleaning on 30 July, and a new cook joining on 5 August. Which event is the most likely exposure?
1. AThe picnic on 2 July
2. BThe tank cleaning on 30 July
3. CThe feast on 18 July
4. DThe cook joining on 5 August
Answer and explanation in LearnFree account
Question 17 · Easy
Every week, an ANM at a sub-centre reports the number of people seen with fever with rash, acute flaccid paralysis and acute watery diarrhoea, based on symptoms alone, under the Integrated Disease Surveillance Programme. Which reporting format is she using?
1. AP form (presumptive)
2. BAnnual morbidity return
3. CL form (laboratory)
4. DS form (syndromic)
Answer and explanation in LearnFree account
Question 18 · Easy
A port health officer in Kochi asks which condition, if detected even once, goes to WHO through the national IHR focal point straight away, without applying the IHR (2005) decision instrument. Which one?
1. APlague
2. BCholera
3. CYellow fever
4. DWild-type polio
Answer and explanation in LearnFree account
Question 19 · Easy
A district surveillance officer receives a report of six children with jaundice from one village. According to the classic steps of investigating an epidemic in Park, what is the first step?
1. ADrawing a spot map of all cases
2. BTesting a hypothesis analytically
3. CVerifying the diagnosis of reported cases
4. DWriting and sending the outbreak report
Answer and explanation in LearnFree account
Question 20 · Medium
A 4-year-old girl is brought to a CHC with weakness of the left leg that began suddenly 3 days ago after a fever; the limb is floppy with absent knee jerk and normal sensation. The medical officer notifies her as acute flaccid paralysis. What is the most appropriate specimen collection?
1. ATwo stool samples 24 hours apart, within 14 days of onset
2. BPaired sera for poliovirus antibodies
3. CCSF for poliovirus culture
4. DOne stool sample after the 60-day follow-up visit
Answer and explanation in LearnFree account
Question 21 · Medium
In a malaria-endemic block, multipurpose health workers visit every house once a fortnight, ask about fever since the last visit and take a blood smear or RDT from each person with fever. What type of surveillance is this?
1. APassive surveillance
2. BActive surveillance
3. CSentinel surveillance
4. DLaboratory-based surveillance
Answer and explanation in LearnFree account
Question 22 · Hard
In a residential school, 40 students develop hepatitis A over 10 days, about a month after a single day when a tanker supplied untreated water. A month after that peak, a second, smaller wave of 12 cases occurs, mostly in students who had not drunk the tanker water but shared rooms and toilets with the first cases. What best describes this outbreak?
1. ATwo unrelated point-source outbreaks
2. BCommon-source outbreak with secondary spread
3. CContinuous common-source outbreak
4. DPurely propagated outbreak
Answer and explanation in LearnFree account
Question 23 · Medium
A newly posted district surveillance officer reviews four statements about IDSP reporting: 1. The S form is filled by health workers on the basis of syndromes. 2. The P form is filled by medical officers on a probable clinical diagnosis. 3. The L form is filled by laboratories for confirmed cases. 4. Routine S, P and L reports are sent only once a month. Which statements are correct?
1. A1, 3 and 4 only
2. B2 and 3 only
3. C1 and 4 only
4. D1, 2 and 3 only
Answer and explanation in LearnFree account

Outbreak investigation and surveillance (IDSP, IHIP)

Within 2 to 6 hours of a wedding lunch in a village, 64 of 150 guests develop vomiting and abdominal cramps. The epidemic curve rises sharply to a single peak and falls, with no new cases after the next day. What type of epidemic is this?

Under IDSP, a sudden rise in cases of fever with rash is flagged from a block. Which team is primarily responsible for investigating the outbreak in the field and starting control measures?

All 100 guests at a village wedding are traced after an outbreak of food poisoning. Of the 60 who ate the chicken curry, 45 fell ill; of the 40 who did not, 4 fell ill. Which measure of association should be calculated, and what is its value?

A PHC reports 14 cases of acute diarrhoea in one week from a village where, in the same week of each of the past three years, the PHC recorded about 5 cases. The district surveillance officer compares these figures. What is the purpose of this comparison?

A district surveillance officer explains to new medical officers how outbreak data now reach the state and the Centre through the Integrated Health Information Platform (IHIP). What does IHIP add to IDSP surveillance?

In a town, cases of hepatitis E start rising 4 weeks after a sewage line begins leaking into the drinking-water pipeline. New cases keep appearing at a roughly steady level for 8 weeks, and fall only after the leak is repaired. What shape will the epidemic curve show?

In a residential school, cases of hepatitis A occur in three waves over four months, each wave larger than the last and the peaks separated by about four weeks; the water supply has been tested and found safe. What type of epidemic is this?

During a typhoid outbreak in a town, the team selects 40 cases and 80 healthy neighbourhood controls. Eating pani puri from one street vendor is reported by 30 cases and 20 controls. What is the odds ratio for this exposure?

Every week, an ANM at a sub-centre reports the number of people seen with fever with rash, acute flaccid paralysis and acute watery diarrhoea, based on symptoms alone, under the Integrated Disease Surveillance Programme. Which reporting format is she using?

A port health officer in Kochi asks which condition, if detected even once, goes to WHO through the national IHR focal point straight away, without applying the IHR (2005) decision instrument. Which one?

A district surveillance officer receives a report of six children with jaundice from one village. According to the classic steps of investigating an epidemic in Park, what is the first step?

A 4-year-old girl is brought to a CHC with weakness of the left leg that began suddenly 3 days ago after a fever; the limb is floppy with absent knee jerk and normal sensation. The medical officer notifies her as acute flaccid paralysis. What is the most appropriate specimen collection?

In a malaria-endemic block, multipurpose health workers visit every house once a fortnight, ask about fever since the last visit and take a blood smear or RDT from each person with fever. What type of surveillance is this?