RATIONALE FOR SURVEILLANCE
Haemophilus influenzae type b (Hib) is the main cause of bacterial meningitis in children, and one of the 2 most common causes of severe bacterial pneumonia, which is the largest single remaining infectious disease killer of young children in the developing world. Hib may also cause other diseases, including arthritis, skin infection, and epiglottitis. Surveillance is critical to clarify the impact of disease and that of immunization programmes. In many countries, Hib pneumonia is more common than the other types of respiratory infection, but diagnosis of Hib pneumonia is extremely difficult. Routine surveillance should concentrate on meningitis and other Hib infections, diagnosed with microbiological tests on blood, cerebrospinal fluid (CSF), and other body fluids (such as pleural fluid) that usually do not contain bacteria. Such infections are often termed "invasive Hib disease". Countries may also wish to report potential cases of bacterial meningitis, both as a performance indicator for Hib detection and to clarify the burden of meningitis attributable to all bacteria.
RECOMMENDED CASE DEFINITION
Bacterial meningitis is characterized by fever of acute onset, headache and stiff neck. Meningitis is not a specific sign for Hib disease, and Hib disease cannot be diagnosed on clinical grounds.
Laboratory criteria for diagnosis
Culture: isolation of Hib from a normally sterile clinical specimen, such as cerebrospinal fluid (CSF) or blood. Culture of Hib from non-sterile sites such as the throat, where bacteria can grow without causing disease, does not define Hib disease.
Antigen detection: identification of Hib antigen in normally sterile fluids, by methods such as latex agglutination or counter-immunoelectrophoresis (CIE).
Potential: (bacterial meningitis case): a child with a clinical syndrome consistent with bacterial meningitis.
Probable: Not applicable.
Confirmed: A case that is laboratory-confirmed (growth or identification of Hib in CSF or blood).
Note: Any person with Hib isolated from CSF or blood may be reported as a confirmed case, regardless of whether their clinical syndrome was meningitis.
RECOMMENDED TYPES OF SURVEILLANCE
• Routine monthly reporting of aggregated data of confirmed cases is recommended from peripheral level to intermediate and central levels
• Zero reporting must be required at all levels
• All potential cases should also be reported if laboratory performance indicators are to be monitored*
* Laboratory confirmation is required for all cases, and the extent of surveillance will vary depending on the capabilities of individual countries. Surveillance does not need to be national in scope to fulfil goals (see "Rationale" section). It is more important to have a well-functioning system in some areas than to have a nation-wide system that functions poorly.
RECOMMENDED MINIMUM DATA ELEMENTS
Aggregated data for reporting
• Number of cases
• Number of 3rd doses of Hib vaccine (Hib3) administered to infants
CASE-BASED DATA FOR REPORTING AND INVESTIGATION
• Unique identifier
• Geographical area (e.g., district and province) names
• Date of birth
• Date of onset
• Specimen type, if specimen collected: 1 = blood; 2 = CSF; 3 = both; 4 = other
• Culture result, if done: 1 = positive; 2 = negative; 3 = pending; 4 = not done
• Antigen detection result, if done: 1 = positive; 2 = negative; 3 = pending; 4 = not done
• CSF white cell count/ml, if done
• Outcome: 1 = alive; 2 = dead; 9 = unknown
• Number of Hib doses received: 9 = unknown
• Final classification: 1 = potential; 2 = confirmed
RECOMMENDED DATA ANALYSES, PRESENTATION, REPORTS
• Incidence rate by year and geographic area
• Hib3 coverage by year and geographic area
• Completeness and timeliness of reporting
Same as aggregated, plus:
• Age-specific incidence rate
• Case-fatality rate
• Cases by immunization status
Performance Indicators of surveillance quality
% of potential bacterial meningitis cases in which CSF/blood was obtained
% potential bacterial meningitis cases w/bacterial pathogen identified from CSF/blood:
• Among CSF with 10 or more white blood cells/ml
• Among CSF with 100 or more white blood cells/m
Although persons with bacterial meningitis have a wide range of CSF white blood cell counts, potential bacterial meningitis cases with identifiable bacterial causes are more common in cases with increasing CSF cell counts. For evaluation of performance, programme personnel may wish to determine the proportion of potential bacterial meningitis cases in which bacterial causes have been identified in one or both of the above categories. Results below the target levels suggest some cases of bacterial meningitis are not being identified - review of laboratory/clinical practices required.
PRINCIPAL USES OF DATA FOR DECISION-MAKING
• Determine incidence of Hib meningitis and invasive disease to estimate burden of Hib disease
• Measure impact of immunization programme/identify areas needing more input
• Monitor coverage and take action to correct low coverage areas
Surveillance requires laboratory confirmation, and nation-wide surveillance may not be practical in many countries. Surveillance in areas with appropriate clinical and laboratory capacity can provide information on the impact of both disease and immunization. A combination of nation-wide immunization coverage data and area-specific disease data can provide information for decisions on immunization programmes. For further guidance on surveillance methods, see document WHO/VRD/GEN/95.05 Generic protocol for population-based surveillance of Haemophilus influenzae type b.
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)
Tel: (41 22) 791 4511/4410
Fax: 4193 or (4122) 7910746 attn VAB