RATIONALE FOR SURVEILLANCE

Diphtheria is a widespread severe infectious disease that has potential for epidemics. The control of diphtheria is based on the following 3 measures:

 

1. Primary prevention of disease by ensuring high population immunity through immunization.

2. Secondary prevention of spread through rapid investigation of close contacts, in order to ensure proper treatment.

3. Tertiary prevention of complications and deaths through early diagnosis and proper management.

Surveillance data can be used to monitor levels of immunization coverage (target >90%) and disease as a measure of the impact of control programmes. Recent epidemics have highlighted the need for adequate surveillance and epidemic preparedness.

RECOMMENDED CASE DEFINITION

Clinical description

An illness of the upper respiratory tract characterized by laryngitis or pharyngitis or tonsillitis, and

 

• adherent membranes of tonsils, pharynx and/or nose

Laboratory criteria for diagnosis

Isolation of Corynebacterium diphtheriae from a clinical specimen.

 

Note: A rise in serum antibody (fourfold or greater) is of interest only if both serum samples were obtained before administration of diphtheria toxoid or antitoxin. This is not usually the case in surveillance, where serological diagnosis of diphtheria is thus unlikely to be an issue.

Case classification

Suspected: Not applicable.

Probable: A case that meets the clinical description.

Confirmed: A probable case that is laboratory confirmed or linked epidemiologically to a laboratory confirmed case.

 

Note: Persons with positive C. diphtheriae cultures who do not meet the clinical description (i.e. asymptomatic carriers) should not be reported as probable or confirmed diphtheria cases.

RECOMMENDED TYPES OF SURVEILLANCE

 

• Routine monthly reporting of aggregated data of probable or confirmed cases is recommended from peripheral level to intermediate and central levels; zero reporting required at all levels

• All outbreaks must be investigated immediately and case-based data collected

• In countries achieving low incidence (usually where immunization coverage is >85% - 90%) immediate reporting of case-based data for probable or confirmed cases is recommended from peripheral to intermediate and central levels

Aggregated data on probable of confirmed cases and on immunization coverage must be reported from national level to WHO Regional Offices according to regional specifications.

RECOMMENDED MINIMUM DATA ELEMENTS

Aggregated data:

 

• Number of cases
• Number of third doses of diphtheria-tetanus-pertussis vaccine (DTP3) administered to infants

Case-based data:

 

• Unique identifier

• Geographical area (e.g., district) name

• Date of birth

• Date of onset

• Date of first treatment

• Treatment type:

 

1 = antibiotic & antitoxin; 2 = antibiotic only; 3 = antitoxin only; 4 = no or other treatment; 9 = unknown

 

• Laboratory result:

 

1 = toxigenic C. diphtheriae isolated; 2 = non-toxigenic C. diphtheriae isolated; 3 = C. diphtheriae isolated, toxigenicity unknown; 4 = C. diphtheriae not isolated; 6 = no specimen processed; 9 = unknown

 

• Total number of doses of diphtheria vaccine (DPT, DT or Td) received

• Date of last dose

• Final classification of the case:

 

1 = confirmed; 2 = probable; 3 = discarded

 

• Outcome:

 

1 = alive; 2 = dead; 3 = unknown

RECOMMENDED DATA ANALYSES, PRESENTATION, REPORTS

Aggregated data:

 

• Incidence rate by month, year, and geographic area
• DPT3 coverage by year and geographic area
• Completeness/timeliness of monthly reporting
• Proportional morbidity (compared to other diseases of public health importance)

Case-based data: same as aggregated data plus the following:

 

• Age-specific incidence rate
• Cases by immunization status, laboratory results, treatment type
• Cases treated "on time" (≤7 days of onset)
• Case-fatality rate
• Proportional mortality (compared to other diseases of public health importance)

PRINCIPAL USES OF DATA FOR DECISION-MAKING

 

• Monitor case-fatality rate and, if high, determine cause (e.g., poor case management, lack of antibiotics/anti-toxin, patients not seeking treatment in time) so that corrective action can be taken

• Determine age-specific incidence rate, geographical area, and season of diphtheria cases, to know risk groups and risk period

• Monitor incidence rate to assess impact of control efforts

• Monitor immunization coverage per geographical area to identify areas of poor programme performance

• Detect outbreaks and implement control measures

• Investigate outbreaks to understand epidemiology, determine why the outbreak occurred (e.g., vaccine failure, failure to immunize, accumulation of susceptibles, waning immunity, new toxigenic strain), and ensure proper case management

 

Note: In addition to surveillance, carefully designed serologic studies can be used to monitor the immune status of different age groups.

SPECIAL ASPECTS

Further information is available from the Expanded Programme on Immunization.

CONTACT

Regional Offices

See Regional Office contacts on section "Communicable disease contacts in Regional Offices".

Headquarters: 20 avenue Appia, CH-1211 Geneva 27, Switzerland

Vaccines and Other Biologicals (VAB)/Expanded Programme on Immunization (EPI)

 

E-mail: wengerj@who.ch / gpv@who.ch
Tel: (41 22)791 4511/4410
Fax: 4193 or (4122) 7910746 attn VAB