Case definitions of diseases and syndromes under surveillance

IDSP training module for state and district surveillance officers

Module 5

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

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

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

specifi

city

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

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

Epidemiologically linked case

1. The patient had contact with one or more persons who:• Have/had the disease • Have been exposed to a point source of

infection

2. Transmission of the agent by the usual modes of transmission is plausible

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

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

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

Other conditions under surveillanceType 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

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

Laboratory criteria for malaria diagnosis

• Demonstration of malaria parasite on blood film

• Positive rapid diagnostic test for malaria

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

* State may set their own triggers

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

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

Laboratory criteria for cholera diagnosis

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

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

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

Typhoid fever: Clinical case description

• Any person with fever for >1 week • Any TWO of the following:

Toxic look Coated tongue Relative bradycardia Splenomegaly

Laboratory criteria for diagnosis of typhoid fever

• Serology Typhi dot / Widal test positive

• Isolation of organism from clinical specimen (blood)

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

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

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

Measles clinical case definition

• Any person with Fever Maculo-papular rash lasting for more than 3

days Cough or coryza or conjunctivitis

Laboratory criteria for measles diagnosis

• Presence of measles specific IgM antibodies

• Isolation of measles virus• At least a four fold increase in antibody

titres

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

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

Laboratory criteria for polio diagnosis

• Isolation of a wild poliovirus from stool specimen

Polio case classification

• Suspect Syndromic case of acute flaccid paralysis

• Probable Epidemiologically linked case

• Confirmed Suspected case that is laboratory confirmed

Polio trigger

• Even a single case will trigger outbreak investigations

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

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

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

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

Plague: Triggers

• Trigger 1 Rat fall

• Trigger 2 At least 1 probable case of plague in

community

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

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)

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

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

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

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

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

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

Dengue hemorrhagic fever

• Probable or confirmed case of Dengue fever with1. One or more criteria of hemorrhagic tendency

• Positive tourniquet test• Petichiae, ecchymoses or purpura• Bleeding from mucosa / GIT/ injection site

2. Thrombocytopenia3. Evidence of plasma leakage as manifested by:

• Pleural effusion• Ascitis• Hypo-proteinemia

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

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

Acute viral hepatitis: Clinical case description

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

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

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.

Laboratory criteria for the diagnosis of HIV infection

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

Syndromes under surveillance

• Fever• Cough• Diarrhea• Acute flaccid paralysis• Jaundice• Unusual syndrome causing

death/ hospitalization

Fever

1. 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)

2. Fever > 7 days Suspected typhoid

• Triggers More than 2 similar case in the village (1000 Population)

Cough

• Short duration (Cough < 3 weeks) Suspected acute respiratory tract infection

• Longer duration (Cough of > 3 weeks) Suspected tuberculosis

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 < 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

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

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

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

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