• Malaria
• Poliomielytis

Diseases under epidemiological surveillance by WHO, established by the 22^nd World Health Assembly, are louseborne typhus fever and relapsing fever, paralytic poliomyelitis, malaria and influenza. From this group of maladies, this issue of the Epidemiological Bulletin presents –in addition to its case definitions- a summary of some guidelines for epidemiological surveillance for paralytic poliomyelitis and malaria, taken from the WHO Recommended Surveillance Standards, 2^nd. Ed., June 1999, revised by the PAHO’s Communicable Diseases Program.

MALARIA

Malaria is one of the most prevalent tropical disease, with high morbidity and mortality and high economical and social burden. The four elements of the Global Strategy for Malaria Control that make its surveillance essential are: (1) provision of early diagnosis and treatment; (2) planning and implementing selective and sustainable preventive measures, including vector control; (3) early detection, containment and prevention of epidemics; (4) strengthening local capacities in basic and applied research to promote the regular assessment of a country’s malaria situation, in particular the ecological, social and economic determinants of the disease.

Recommended case definition: (For use in endemic areas and people exposed to malaria, e.g., a history of visit to endemic area). Malaria must be defined in association with clinical disease symptoms. The case definition for malaria will vary according to how malaria is perceived in a given country, local patterns of transmission, and disease consequences. The suggested definitions are deliberately broad. They must be adapted and used with additional indicators to make them more applicable to local and national epidemiology and control targets.

Clinical description: Most patients experience fever with intermittent periods of chills and sweating. Splenomegaly and anemia are commonly associated signs. Common but non-specific symptoms include otherwise unexplained headache, back pain, chills, sweating, myalgia, nausea, vomiting. Untreated Plasmodium falciparum infection can lead to severe malaria: any CNS disturbances, coma, generalized convulsions, anuria, hyperparasitemia, normocytic anemia, disturbances of fluid, electrolyte, and acid-base balance, renal failure, hypoglycemia, hyperpyrexia, hemoglobinuria, circulatory collapse/shock, spontaneous bleeding (disseminated intravascular coagulation), pulmonary edema, and death.

Laboratory criteria for diagnosis: Demonstration of the Plasmodium or its antigens in blood or tissues.

Case classification:

1. In areas without access to laboratory-based diagnosis:
   • Probable uncomplicated malaria: a person with symptoms and/or signs of malaria who receives antimalarial treatment.
   • Probable severe malaria: a patient who requires hospitalization for symptoms and signs of severe malaria and receives antimalarial treatment.
   • Probable malaria death: death of a patient diagnosed with probable severe malaria.

2. In areas with access to laboratory-based diagnosis:
   • Asymptomatic malaria: a person with no recent history of symptoms and/or signs of malaria who shows laboratory confirmation of parasitemia.
   • Confirmed uncomplicated malaria: a patient with symptoms and/or signs of malaria who received antimalarial treatment, with laboratory confirmation of diagnosis.
   • Confirmed severe malaria: a patient who requires hospitalization for symptoms and/or signs of severe malaria and receives antimalarial treatment, with laboratory confirmation of diagnosis.
   • Confirmed malaria death: death of a patient diagnosed with severe malaria, with laboratory confirmation of diagnosis.
   • Malaria treatment failure: a patient with uncomplicated malaria without any clear symptoms suggesting another concomitant disease, who has taken a correct dosage of antimalarial treatment, and who presents with clinical deterioration or recurrence of symptoms within 14 days of the start of treatment, in combination with parasitemia (asexual forms).

Recommended types of surveillance: The primary purpose of surveillance is to guide malaria control activities at the level where data are collected, in order to get a numeric picture of trends in malaria incidence and mortality. These types of surveillance include (1) routine weekly analysis at peripheral level: collection, aggregation, graphic representation of malaria cases (endemic corridor or mapping), and reporting to the intermediate level; (2) at the intermediate level: monthly aggregation and analysis of the peripheral level data, evaluation of trends and decision-making on the needs detected for the peripheral level; (3) surveys built into the supervision and retraining process; (4) monitoring of therapeutic failures and drug efficacy testing; (5) timely recognition of malaria epidemic and notification at all times.

Recommended minimum data elements: Different segments of the population may be affected by malaria. All malaria data and case classification must be reported by age group (A) and sex (S), with a separate category for pregnant women (P); these minimum data elements are vital information. Where there are laboratory facilities, type of malaria parasite must be recorded. In addition, malaria treatment failure should be reported.

Recommended data collection and analyses: Disease trends and patterns are the principal concern of malaria control programs. Thus, it is recommended that (1) local level health workers prepare weekly reports with aggregated minimum data and the above mentioned variables in graphs or mapping, by probable place of infection; (2) monthly reports of aggregated data to the next level, by geographical area; (3) graphs of time trends for the different geographical areas to detect an increase in the number of cases of more than 2 standard deviations (compared to averaged data from the same week of previous years), which may indicate an epidemic; (4) maps with the presence/absence of malaria cases, report completeness and timeliness; and (5) a line list for peripheral and intermediate levels that sent no monthly report or untimely reports.

Principal uses of data for decision-making include (1) identify high risk groups and the problem areas; (2) evaluate impact of control measures; (3) readjust and target control measures; and (4) guide allocation of resources and training efforts.

POLIOMIELYTIS

Rationale for Surveillance: Targeted for eradication (item 6.1 of the WHO General Program of Work, 9GPW6.1) although eradicated in the Americas, this disease requires highly sensitive surveillance for acute flaccid paralysis (AFP), including immediate case investigation and the specimen collection, which are critical to detect wild poliovirus circulating in every infected geographical area. A polio eradication program should use the following standardized case definitions, revised from the PAHO’s Polio Eradication Field Guide, 2^nd. Ed., 1994, and the WHO Recommended Surveillance Standards from the 2^nd. Ed., June 1999, revised by the PAHO’s Communicable Diseases Program.

Recommended Case Definitions:

• Suspected case: any case of acute-onset flaccid paralysis (AFP) -including Guillain-Barré syndrome- in a person under 15 years of age for any reason other than severe trauma, or paralytic illness in a person of any age in which polio is suspected. The classification "suspected case" is temporary. It should be reclassified as "probable" or "discarded" within 48 hours of notification.
• Probable case: a case in which AFP is found, and no other cause for the paralysis can be identified immediately. The classification of "probable case" is also temporary; within 10 weeks of onset the case should be reclassified as "confirmed", "compatible", "vaccine-associated" or "discarded."
• Confirmed case: a case with acute paralytic illness with or without residual paralysis, and isolation of wild poliovirus from the stools of either the case or its contacts.
• Polio-compatible case: a case in which one adequate stool specimen was not collected from a probable case within 2 weeks of the onset of paralysis, and there is either an acute paralytic illness with polio-compatible residual paralysis at 60 days, or death takes place within 60 days, or the case is lost to follow-up.
• Vaccine-associated Paralytic Poliomyelitis: a case with acute paralytic illness in which vaccine-like poliovirus is isolated from stool samples, and the virus is believed to be the cause of the disease. There are two possible types of vaccine-associated paralytic poliomyelitis (VAPP): recipient and contact. A case classified as a recipient is a person who has onset of AFP 4 to 40 days after receiving OPV and has neurologic sequelae compatible with polio 60 days after the paralysis began. A case is classified as a contact VAAP when a person who has residual paralysis 60 days after the onset of AFP had contact 4 to 40 days before the paralysis began with a person who received OPV somewhere between 4 and 85 days before the contact's paralysis began.
• Discarded (Not Poliomyelitis): a case with acute paralytic illness for which one adequate stool specimen was obtained within 2 weeks after onset of paralysis and was negative for poliovirus.
  

Recommended Surveillance Measures:

• The reporting system must cover key hospitals and clinics and have at least one reporting source for every geopolitical unit;
• The concept of reporting all AFP cases rather than only poliomyelitis cases must be emphasized;
• Weekly reporting of AFP is critical;
• The concept of negative reporting of AFP must be included in the weekly reporting system;
• The reporting system for AFP must continually be monitored and revitalized;
• Immediate response to reports in the surveillance system by trained epidemiologists must occur for every suspected case within 48 hours;
• Cooperation from the private medical community is essential for all surveillance efforts;
• The public needs to be informed about the importance of and procedure for reporting AFP;
• Feedback to all participants of the surveillance system is essential.

Recommended Minimum Data Elements: Case-based data (to be linked to specimen-based data for analysis): (i) unique identifier; (ii) geographical area (district and province) name; (iii) date of birth; (iv) date of onset of paralysis; (v) date of notification; (vi) date of case investigation; (vii) total poliomyelitis vaccine doses received; (viii) fever at onset of paralysis; (ix) progression of paralysis within 4 days; (x) asymmetric paralysis; (xi) date of 60-day follow-up examination; (xii) findings at 60-day follow-up; (xiii) final classification.

Specimen-based data (to be linked to case-based data for analysis): (i) unique identifier; (ii) specimen number; (iii) date of paralysis onset; (iv) date of last OPV; (v) date of stool specimen collection; (vi) date stool specimen sent to laboratory; (vii) date specimen received in laboratory; (viii) condition of stool; (ix) date final culture results sent from laboratory to EPI; (x) date intra-typic differentiation results sent from laboratory to EPI; (xi) results of stool samples.

Principal Uses of Data for Decision-Making:

• One polio case must be considered as an outbreak.
• Track wild poliovirus circulation.
• Classify cases as confirmed, poliomyelitis compatible or discarded
• Monitor routine coverage for immunizations in all geographical areas and focus efforts in low performing geographical areas.
• Identify high-risk areas for planning mopping up immunization.
• Monitor performance of surveillance using standard indicators and focus efforts in low performing areas.
• Provide evidence for polio-free certification.
• Conduct two National Immunization Days (NIDs) a year in countries with < 80% of districts with OPV3 > 95%.

Surveillance Indicators for Certification:

• AFP rate per 100,000 children < 15 years of age.
• % AFP cases with one stool taken within 15 days of paralysis onset.
• % AFP cases investigated within 48 hours of notification date
• % of reporting sites registered each week.

Return to the Index,
Epidemiological Bulletin , Vol. 20 No. 2, June 1999