1. Case definitions of diseases and syndromes under surveillance
IDSP training module for state and district surveillance officers
Module 5

2. Learning objectives
Describe why case definitions for diseases are crucial for disease surveillance
List the diseases/syndromes under surveillance in state and define what is probable /suspected /confirmed case
List laboratory criteria for the diseases under surveillance
Describe correctly why trigger levels are specified and the response to trigger level 1 and 2

3. Key principles of the Integrated Disease Surveillance Programme
Monitor a limited number of health conditions
Integrate surveillance activities under various programmes
Use laboratories in surveillance
Set up of district and state surveillance units
Involve private sector and medical colleges
Take advantage of information technologies

4. Types of case definitions in use
Criteria
Who uses it
Syndromic
Clinical pattern
Paramedical personnel and members of community
Presumptive
Typical history and clinical examination
Medical officers of primary and community health centres
Confirmed
Clinical diagnosis by a medical officer and positive laboratory identification
Medical officer and
Laboratory staff
More specificity
Though it is ideal to have all disease under surveillance confirmed by laboratory tests. This is often not feasible. During routine surveillance the diagnosis made by the Medical Officer is considered presumptive in nature. The validity of presumptive diagnosis of surveillance conditions will be higher than that of the syndromic one undertaken by the health worker.
Under IDSP the MOs of PHC, CHC, Medical Colleges & Sentinel surveillance will carry out presumptive surveillance routinely. This will be supplemented by confirmed diseases by laboratory reporting.

5. Rationale for the use of case definitions
Uniformity in case reporting at district, state and national level
Use of the same criteria by reporting units to report cases
Compatibility with the case definitions used in WHO recommended surveillance standards
Allow international information exchanges

6. Levels of case definitions
Suspect case
A case that meets the clinical case definition
Probable case
A suspect case that is diagnosed by a medical officer
Confirmed case
A suspect case that is laboratory confirmed
i.e., a single source of infection, such as an event leading to a foodborne-disease outbreak, to which all confirmed case-patients were exposed)

7. Epidemiologically linked case
The patient had contact with one or more persons who:
Have/had the disease
Have been exposed to a point source of infection
Transmission of the agent by the usual modes of transmission is plausible
i.e., a single source of infection, such as an event leading to a foodborne-disease outbreak, to which all confirmed case-patients were exposed)

8. Triggers
Threshold for diseases under surveillance that trigger pre-determined actions at various levels
Based upon the number of cases in weekly report
Trigger levels depend on:
Type of disease
Case fatality (Death / case ratio)
Number of evolving cases
Usual trend in the region

9. Levels of response to different triggers
Significance
Levels of response 1
Suspected /limited outbreak
Local response by health worker and medical officer 2
Outbreak
Local and district response by district surveillance officer and rapid response team 3
Confirmed outbreak
Local, district and state 4
Wide spread epidemic
State level response 5
Disaster response
Local, district, state and centre

10. Conditions under regular surveillance
Type of disease
Disease
Vector borne diseases
Malaria
Water borne diseases
Diarrhea (Cholera)
Typhoid
Respiratory diseases
Tuberculosis
Vaccine preventable diseases
Measles
Disease under eradication
Polio
Other conditions
Road traffic accidents
International commitment
Plague
Unusual syndromes
Meningo-encephalitis
Respiratory distress
Hemorrhagic fever

11. Other conditions under surveillance
Type of surveillance
Categories
Conditions
Sentinel surveillance
STDs
HIV/HBV/HCV
Other conditions
Water quality
Outdoor air quality
Regular surveys
Non communicable disease risk factors
Anthropometry
Physical activity
Blood pressure
Tobacco, blood pressure
Nutrition
Blindness
Additional state priorities
Up to five diseases

12. Malaria: Clinical case description
Any patient with fever with any of the following:
Chills, sweating, jaundice or splenomegaly
Convulsions, coma, shock, pulmonary edema and death may be associated in severe cases

13. Laboratory criteria for malaria diagnosis
Demonstration of malaria parasite on blood film
Positive rapid diagnostic test for malaria

14. Malaria case classification
Suspect
Any case of fever
Probable
Case that meets the clinical case definition
Confirmed
A suspected/probable case that is laboratory-confirmed

15. Malaria: Outbreak definition*
Trigger 1
Single case of smear positive in an area where malaria was not present for a minimum of three months
Slide positivity rate doubling over last three months
Single death from clinically /microscopically proven malaria
Single falciparum case of indigenous origin in a free region
Trigger 2:
Two fold rise in malaria in the region over last 3 months
More than five cases of falciparum of indigenous origin
* State may set their own triggers

16. Cholera: Clinical case description
In an area where the disease is not known to be present
Severe dehydration or death from acute watery diarrhoea in a patient aged 5 years or more
In an area where cholera is endemic
Acute watery diarrhea, with or without vomiting in a patient aged 5 years or more
In an area where there is a cholera epidemic
Acute watery diarrhoea, with or without vomiting, in any patient
Cholera does appear in children under 5 years; however, the inclusion of all cases of acute watery diarrhoea in the 2-4 year age group in the reporting of cholera greatly reduces the specificity of reporting. For management of cases of acute watery diarrhoea in an area where there is a cholera epidemic, cholera should be suspected in all patients.

17. Laboratory criteria for cholera diagnosis
Isolation of Vibrio cholera O1 or O139 from stools in any patient with diarrhea 

18. Cholera case classification
Suspect case
A case that meets the clinical case definition
Probable case
A suspect case that is diagnosed by the medical officer
Confirmed case
A suspected case that is laboratory- confirmed

19. Cholera: Outbreak definitions
Trigger 1
A single case of cholera / epidemiologically linked cases of diarrhea
A case of severe dehydration / death due to diarrhea in a patient of >5 years of age
Clustering of cases in a particular village / urban ward where more than 10 houses have at least one case of loose stools irrespective of age per 1000 population
Trigger 2
More than 20 cases of diarrhea in a village/geographical area of 1000 population

20. Typhoid fever: Clinical case description
Any person with fever for >1 week
Any TWO of the following:
Toxic look
Coated tongue
Relative bradycardia
Splenomegaly

21. Laboratory criteria for diagnosis of typhoid fever
Serology
Typhi dot / Widal test positive
Isolation of organism from clinical specimen (blood)

22. Typhoid fever: Case classification
Probable case
Case of fever diagnosed by medical officer that is compatible with:
Clinical case description
Typhi dot/Widal test positive
Epidemiological link to a confirmed case
Confirmed case
Probable case that is laboratory confirmed by:
Isolation of S. typhi/ S. paratyphi from blood
Four fold rise in antibody titres in paired sera 10 days apart

23. Typhoid fever: Outbreak definitions
Trigger 1
More than 30 cases in a week from the entire primary health centre area
5 or more cases per week from one sub-centre of 5,000 population
More than 2 cases from a single village/urban ward/1000 population
Clustering of cases of fever
Trigger 2
More than 60 cases from a primary health centre or more than 10 cases from a sub-center

24. Tuberculosis: Case classification
Suspect
Any person with cough >3 weeks
Probable
Patient with symptoms suggestive of tuberculosis (cough >3 wks with or without fever) diagnosed by medical officer as tuberculosis with or without radiological signs consistent with pulmonary tuberculosis
Confirmed
A case that meets clinical case definition and that is positive for laboratory criteria

25. Measles clinical case definition
Any person with
Fever
Maculo-papular rash lasting for more than 3 days
Cough or coryza or conjunctivitis

26. Laboratory criteria for measles diagnosis
Presence of measles specific IgM antibodies
Isolation of measles virus
At least a four fold increase in antibody titres

27. Measles: Case classification
Suspect
Any case with fever and rash
Probable
Suspect case who is diagnosed as measles by medical officer on basis of clinical case description
Confirmed
A probable case that is:
Laboratory confirmed
Linked epidemiologically to a laboratory confirmed case

28. Polio: Clinical description of acute flaccid paralysis
Any child:
Aged <15 years
Acute onset of flaccid paralysis for which no obvious cause (such as serve trauma or electrolyte imbalance) is found
OR:
Paralytic illness in a person of any age in which polio is suspected

29. Laboratory criteria for polio diagnosis
Isolation of a wild poliovirus from stool specimen

30. Polio case classification
Suspect
Syndromic case of acute flaccid paralysis
Probable
Epidemiologically linked case
Confirmed
Suspected case that is laboratory confirmed

31. Polio trigger
Even a single case will trigger outbreak investigations

32. Plague: Clinical case description
Rapid onset of fever,chills, headache, severe malaise with:
Bubonic form:
Extreme painful swelling of lymph nodes in axilla, groin and neck (bubos)
Pneumonic form:
Cough with blood stained sputum, chest pain and dyspnea
Septicemic form:
Toxic changes in patient

33. Laboratory criteria for plague diagnosis
Giemsa smear positive
Direct fluorescent antibody testing of smears
PCR test
4 fold increase in antibody titres against F1 antigen
Isolation of the bacteria by culture

34. Criteria to define a probable case of plague
A case consistent with clinical case description with history of rat fall
Y.pestis F1 antigen detected in clinical materials by direct fluorescent antibody testing or by some other standardized antigen detection method
Isolate from a clinical specimen demonstrates biochemical reactions consistent with Y.pestis or PCR positivity
A single serum specimen is found positive for diagnostic levels of antibodies to Y.pestis F1 antigen, not explainable on the basis of prior infection or immunization with an epidemiological link with a confirmed case

35. Criteria to define a confirmed case of plague
Probable case that is laboratory-confirmed
Isolate identified as Y. pestis by phage lysis or cultures OR
A significant (4-fold) change in antibody titres to the F1 antigen in paired serum specimens

36. Plague: Triggers Trigger 1 Trigger 2 Rat fall
At least 1 probable case of plague in community

37. Japanese encephalitis: Clinical case description
Febrile illness of variable severity associated with neurological symptoms ranging from headache to meningitis or encephalitis
Symptoms can include:
Headache, fever, meningeal signs, stupor, disorientation, coma, tremors, paresis (generalized), hypertonia, loss of coordination
The encephalitis cannot be distinguished clinically from other central nervous system infections

38. Presumptive laboratory criteria for Japanese encephalitis diagnosis
Detection of an acute phase anti-viral antibody response through one of the following:
Elevated and stable serum antibody titres of JE virus through ELISA, hemagglutination or virus neutralization assay
IgM antibody to the virus in serum (Appears after 1 week of disease)

39. Confirmatory laboratory criteria for Japanese encephalitis diagnosis
Detection of JE virus, antigen or genome in tissue, blood or other body fluid by immuno-chemistry or immuno-fluorescence or PCR,
JE virus-specific IgM in the CSF
Fourfold or greater rise in JE virus-specific antibody in paired sera through IgM /IgG, ELISA, haemagglutination inhibition test or virus neutralization test

40. Japanese encephalitis: Case classification
Suspect
Any case with fever of acute onset and altered consciousness/ convulsions and change in behaviour
Probable
Any suspected cases diagnosed as Japanese encephalitis by the medical officer
Any suspect case with presumptive laboratory results
A case of fever epidemiologically linked with a proven Japanese encephalitis case
Confirmed
A suspect or probable case confirmed by confirmatory laboratory tests

41. Japanese encephalitis: Triggers
Clustering of two or more similar case from a locality in one week
Trigger 2
More than four cases from a PHC (30,000 population) in one week

42. Dengue fever: Clinical case description
An acute febrile illness of 2-7 days duration with 2 or more of the following:
Headache
Retro-orbital pain
Myalgia
Arthralgia
Rash
Hemorrhagic manifestations
Leucopenia

43. Probable case classification of Dengue fever
A case diagnosed by medical officer as Dengue fever based on the clinical case definition OR
A case with fever with blood negative for malaria and not responding to anti-malarials
WITH
Supportive serology (reciprocal hemagglutination-inhibition antibody titre, comparable IgG EIA titre or positive IgM antibody test in late acute or convalescent-phase serum specimen)
Epidemiological link with a confirmed case
High vector density

44. Confirmed case of Dengue fever
Isolation of the dengue virus from serum, plasma, leukocytes or autopsy samples
Demonstration of a four fold or greater change in reciprocal IgG or IgM antibody titres to one or more dengue virus antigens
Demonstration of dengue virus antigen in autopsy tissue
Detection of viral genomic sequences in autopsy tissue, serum or CSF samples

45. Dengue hemorrhagic fever
Probable or confirmed case of Dengue fever with
One or more criteria of hemorrhagic tendency
Positive tourniquet test
Petichiae, ecchymoses or purpura
Bleeding from mucosa / GIT/ injection site
Thrombocytopenia
Evidence of plasma leakage as manifested by:
Pleural effusion
Ascitis
Hypo-proteinemia

46. Dengue shock syndrome A case of Dengue hemorrhagic fever AND
Evidence of circulatory failure manifested by rapid and weak pulse and narrow pulse pressure (<20 mmHg) or hypotension

47. Dengue: Triggers Trigger 1 Trigger 2
Clustering of two similar case of probable Dengue fever in a village
Single case of Dengue hemorrhagic fever
Trigger 2
More than four cases of Dengue fever in a village with population of about 1000

48. Acute viral hepatitis: Clinical case description
Acute jaundice (Yellow sclera/skin)
Dark urine
Anorexia, malaise
Extreme fatigue
Right upper quadrant tenderness

49. Laboratory criteria for acute viral hepatitis diagnosis
HAV
IgM HAV
HBV
Positive for HBsAg and IgM anti-HBc
HCV
Positive anti-HCV
HDV
Positive for HBsAg and anti-HDV
HEV
Positive for IgM HEV

50. Acute viral hepatitis: Case classification
Suspect
As per clinical definition
Confirmed
A suspect case that is laboratory confirmed
For hepatitis A/E, a case compatible with the clinical description and with epidemiological link with a laboratory confirmed case of hepatitis A/E.

51. Laboratory criteria for the diagnosis of HIV infection
HIV positive serology (ELISA)
Confirmation with a second ELISA

52. Syndromes under surveillance
Fever
Cough
Diarrhea
Acute flaccid paralysis
Jaundice
Unusual syndrome causing
death/ hospitalization

53. Fever Fever less than 7 days with: Fever > 7 days Triggers
Rash and coryza or conjunctivitis (suspected measles)
Altered sensorium (suspected Japanese encephalitis or malaria)
Convulsions (suspected Japanese encephalitis )
Bleeding from skin, mucus membrane, vomiting blood or passing fresh blood or black motion (suspected Dengue)
With none of the above (suspected malaria)
Fever > 7 days
Suspected typhoid
Triggers
More than 2 similar case in the village (1000 Population)

54. Cough Short duration (Cough < 3 weeks)
Suspected acute respiratory tract infection
Longer duration (Cough of > 3 weeks)
Suspected tuberculosis

55. Diarrhea Any new case of watery diarrhea Trigger
Passage of 3 or more loose / watery stools in 24 hours
With or without dehydration
Total duration of illness < 14 days
Trigger
More than 10 houses with diarrhea in a village or urban ward or a single case of severe dehydration or death in a patient > than 5 years with diarrhea

56. Jaundice
A new patient with an acute illness (<4 weeks) and following symptoms:
Jaundice, dark urine
Anorexia, malaise, fatigue
Pain in abdomen (right upper quadrant)
Trigger
More than two cases of jaundice in different houses irrespective of age in a village or 1000 population

57. Acute flaccid paralysis
A case of acute flaccid paralysis is defined as any child:
Aged <15 years
Has acute onset of flaccid paralysis for which no obvious cause is found
Trigger
Single case of AFP

58. Points to remember (1/2)
The list of diseases under surveillance must always be remembered
The diseases for which vertical programmes are operative should be clearly known
Case definitions are crucial in accurately identifying the epidemic at the earliest
Trigger levels are important in initiating response activities

59. Points to remember (2/2)
Laboratory confirmation is not mandatory to initiate rapid response measures but specimens should be collected as soon as possible
Clinical syndromes should be identified
Method of transmission of diseases should be identified
Different surveillance methods for the different conditions should be clearly understood