Case definitions of diseases and syndromes under surveillance

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 More specificity

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

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

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

10. Conditions under regular surveillance

11. Other conditions under surveillance

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

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 • Rat fall • Trigger 2 • 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 • Trigger 1 • 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 • 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.