WHO-recommended surveillance standard of diphtheria
Rationale for surveillance
Diphtheria is a widespread severe infectious disease that has the potential for epidemics. The control of diphtheria is based on the following three measures. 1) Primary prevention of disease by ensuring high population immunity through immunization. 2) Secondary prevention of spread by the rapid investigation of close contacts, to ensure their proper treatment. 3) Tertiary prevention of complications and deaths by early diagnosis and proper management. Surveillance data can be used to monitor levels of 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 characterised by laryngitis or pharyngitis or tonsillitis, and an adherent membrane of the tonsils, pharynx and/or nose
Laboratory criteria for diagnosis
Isolation of Corynebacterium diphtheriae from a clinical specimen, or fourfold or greater rise in serum antibody (but only if both serum samples were obtained before the administration of diphtheria toxoid or antitoxin)
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 and not meeting the clinical description (i.e. asymptomatic carriers) should not be reported 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
- Designated reporting sites at all levels should report at a specified frequency (e.g. weekly or monthly) even if there are zero cases (often referred to as "zero reporting")
- All outbreaks should be investigated immediately and case-based data collected
- In countries achieving low incidence (usually where coverage is >85-90%) immediate reporting of case-based data of probable or confirmed cases is recommended from peripheral level to intermediate and central levels
Recommended minimum data elements
Aggregated data
- Number of cases
- Number of third doses of diphtheria toxoid containing vaccine (e.g. DTP3) administered to infants
Case-based data
- Unique identifier
- Geographical area (e.g. district name)
- Date of birth
- Sex: 1=male; 2=female; 9=unknown
- 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; 5=no specimen processed; 9=unknown
- Total diphtheria vaccine (DTP, DT or Td) doses 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 analysis, presentations, reports
Aggregated data
- Incidence rate by month, year, and geographic area
- DTP3 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, sex-specific and district-specific incidence rates by month and year
- Cases by immunization status, laboratory results, treatment type
- Cases treated on time (< seven days of onset)
- Case fatality rate
- Proportional mortality (compared to other diseases of public health importance)
Principal use 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 periods
- 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 immunise, 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
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Lasy Update: 21 February 2014