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

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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

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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

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Types of case definitions in use
Case definition 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
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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

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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

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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

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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

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Levels of response to different triggers
Trigger 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
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Conditions under regular surveillance
Type of disease Disease
Vector borne diseases Malaria
Water borne diseases Diarrhea (Cholera)
Water borne diseases 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
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Other conditions under surveillance
Type of surveillance Categories Conditions
Sentinel surveillance STDs HIV/HBV/HCV
Sentinel surveillance Other conditions Water quality
Sentinel surveillance Other conditions Outdoor air quality
Regular surveys Non communicable disease risk factors Anthropometry
Non communicable disease risk factors Physical activity Blood pressure
Non communicable disease risk factors Physical activity Blood pressure
Non communicable disease risk factors Tobacco, blood pressure
Nutrition
Blindness
Additional state priorities Additional state priorities Up to five diseases
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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

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Laboratory criteria for malaria diagnosis

• Demonstration of malaria parasite on blood film
• Positive rapid diagnostic test for malaria

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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

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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
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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

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Laboratory criteria for cholera diagnosis

• Isolation of Vibrio cholera O1 or O139 from
  stools in any patient with diarrhea 

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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

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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 gt5 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

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Typhoid fever Clinical case description

• Any person with fever for gt1 week
• Any TWO of the following
• Toxic look
• Coated tongue
• Relative bradycardia
• Splenomegaly

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Laboratory criteria for diagnosis of typhoid fever

• Serology
• Typhi dot / Widal test positive
• Isolation of organism from clinical specimen
  (blood)

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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

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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

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Tuberculosis Case classification

• Suspect
• Any person with cough gt3 weeks
• Probable
• Patient with symptoms suggestive of tuberculosis
  (cough gt3 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

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Measles clinical case definition

• Any person with
• Fever
• Maculo-papular rash lasting for more than 3 days
• Cough or coryza or conjunctivitis

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Laboratory criteria for measles diagnosis

• Presence of measles specific IgM antibodies
• Isolation of measles virus
• At least a four fold increase in antibody titres

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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

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Polio Clinical description of acute flaccid
paralysis

• Any child
• Aged lt15 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

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Laboratory criteria for polio diagnosis

• Isolation of a wild poliovirus from stool specimen

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Polio case classification

• Suspect
• Syndromic case of acute flaccid paralysis
• Probable
• Epidemiologically linked case
• Confirmed
• Suspected case that is laboratory confirmed

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Polio trigger

• Even a single case will trigger outbreak
  investigations

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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

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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

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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

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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

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Plague Triggers

• Trigger 1
• Rat fall
• Trigger 2
• At least 1 probable case of plague in community

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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

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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)

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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

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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

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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

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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

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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

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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

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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

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Dengue shock syndrome

• A case of Dengue hemorrhagic fever
• AND
• Evidence of circulatory failure manifested by
  rapid and weak pulse and narrow pulse pressure
  (lt20 mmHg) or hypotension

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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

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Acute viral hepatitis Clinical case description

• Acute jaundice (Yellow sclera/skin)
• Dark urine
• Anorexia, malaise
• Extreme fatigue
• Right upper quadrant tenderness

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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

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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.

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Laboratory criteria for the diagnosis of HIV
infection

• HIV positive serology (ELISA)
• Confirmation with a second ELISA

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Syndromes under surveillance

• Fever
• Cough
• Diarrhea
• Acute flaccid paralysis
• Jaundice
• Unusual syndrome causing
• death/ hospitalization

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Fever

• Fever less than 7 days with
• 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 gt 7 days
• Suspected typhoid
• Triggers
• More than 2 similar case in the village (1000
  Population)

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Cough

• Short duration (Cough lt 3 weeks)
• Suspected acute respiratory tract infection
• Longer duration (Cough of gt 3 weeks)
• Suspected tuberculosis

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Diarrhea

• Any new case of watery diarrhea
• Passage of 3 or more loose / watery stools in 24
  hours
• With or without dehydration
• Total duration of illness lt 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 gt than 5 years with
  diarrhea

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Jaundice

• A new patient with an acute illness (lt4 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

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Acute flaccid paralysis

• A case of acute flaccid paralysis is defined as
  any child
• Aged lt15 years
• Has acute onset of flaccid paralysis for which no
  obvious cause is found
• Trigger
• Single case of AFP

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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

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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