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6.6 Incidence and death rates associated with malaria

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Modified on 2012/11/06 11:01 by MDG Wiki Handbook Categorized as Goal 6
Contents

GOAL AND TARGET ADDRESSED

Goal 6. Combat HIV/AIDS, malaria and other diseases
Target 6.C. Have halted by 2015 and begun to reverse the incidence of malaria and other major diseases

DEFINITION AND METHOD OF COMPUTATION

Definition
The incidence rate of malaria is the number of new cases of malaria per 100,000 people per year.
The death rate associated with malaria is the number of deaths caused by malaria per 100,000 people per year.


Concepts
Malaria is an infectious disease caused by the parasite Plasmodium and transmitted via the bites of infected mosquitoes. Symptoms usually appear between 10 and 15 days after the mosquito bite and include fever, headache, and vomiting. The working definition of a case of malaria is “fever with plasmodium parasites” which defines individuals that require anti-malarial treatment.

Method of computation
The malaria incidence rate (I) is the number of new cases of malaria (M) divided by the total population (Pop) and multiplied by 100,000.
Incidence rate
The malaria death rate (I) is the number of deaths due to malaria (D) divided by the total population (Pop) and multiplied by 100,000.
Death rate

RATIONALE AND INTERPRETATION

Information on the incidence of malaria is required to determine needs for malaria treatment. Data on malaria incidence can be compared to levels of access to malaria treatment to identify underserved populations and, in situations of resource constraint, to target treatment interventions toward high priority areas. Data on changes in malaria incidence help in judging the success of treatment programme implementation, and help to determine whether programmes are performing as expected or whether adjustments in the scale or in the blend of strategies are required. In highly endemic settings, incidence rates are typically as high as 1.5 cases per child under 5 years old per year, and 1 case for every 10 adults per year.

Information on malaria death rates also helps to judge the success of programme implementation and may point to failures of programmes in terms of prevention of malaria or access to effective treatment.

Malaria is serious in its own right, but also increases the risk of death from other conditions. In addition, malaria imposes an economic burden on families, particularly those who are least able to pay for prevention and treatment and most affected by loss of income due to the disease. The disease represents a financial burden to malaria-endemic countries that must use scarce resources to provide bed nets, insecticides and drugs in an effort to control the disease.

SOURCES AND DATA COLLECTION

Information on the number of malaria cases, reporting completeness and case confirmation rates are compiled annually by national ministries of health (National Malaria Control Programs) from data collected by national administrations of health services.

DISAGGREGATION

There are two principal causal agents of malaria according to which incidence and death rates can be disaggregated:
  1. Plasmodium falciparum which is predominant in Africa and other high transmission settings, and is responsible for most severe cases and death; and
  2. Plasmodium vivax which has a wider geographical distribution but is less likely to lead to severe cases of malaria. Countries that confirm malaria cases in laboratories usually provide a breakdown of the proportion of cases due to Plasmodium falciparum and Plasmodium vivax. Some programmes also distinguish between cases that are detected passively (from persons reporting to health facilities) and actively (by searching for cases in communities), and between cases that are indigenous to an area and cases that are likely to have been imported.

It is also useful to examine incidence and death rates by age-group and sex. In low transmission settings where little immunity to malarial disease exists, cases are evenly distributed by age. In high transmission settings, cases and deaths are concentrated in children under five because frequent exposure has enabled older age groups to develop some immunity. The incidence of malaria appears to be evenly distributed across sexes in children, but pregnant women are particularly susceptible to disease.

Compiling incidence rates for occupational groups, urban/rural populations, and income is useful as well. The incidence of disease is higher in certain occupational groups that are exposed to a higher risk of infection, e.g. forest workers, and among rural populations as they generally carry a greater burden of malaria than urban populations. It is likely that differences in incidence exist by wealth quintile (within urban/ rural strata) owing to differences in housing conditions and the availability and use of preventive measures such as insecticide-treated nets (ITNs).

Administrative data on malaria cases are frequently disaggregated by age group (under or over five years of age) and particular risk groups (pregnant women). Other disaggregations are difficult to undertake in a routine setting and require national malaria control programmes to undertake operational research.

COMMENTS AND LIMITATIONS

Estimates of the number of malaria cases are particularly sensitive to the completeness of health facility reporting. If health ministries keep accurate records of the number of surveillance reports received and expected from health facilities, then adjustments can be made for missing reports. However, if this information is not rigorously recorded, and the stated reporting completeness differs from reality then the number of malaria cases will be incorrectly estimated. In addition, many cases recorded in poorly resourced countries are not confirmed by microscopic examination; hence a substantial proportion of patients diagnosed with malaria may have fevers due to other illnesses.

In terms of recording deaths caused by malaria, the symptoms of malaria may be similar to those of other diseases so one cannot always be certain that a death is due to malaria. This is particularly the case with children since many deaths occur in children who may simultaneously suffer from a range of conditions including respiratory infections, diarrhoea, and malnutrition.

In areas of high malaria transmission, parasite prevalence measured through nationally representative household surveys can provide an indication of the risk of malaria infection and trends in disease burden. However, this indicator needs to be treated with caution because many infections may be asymptomatic and not reflect a diseased state. In addition, the indicator does not always reflect changes over time since at high levels of transmission intensity, moderate reductions in inoculation rates do not necessarily translate to reductions in prevalence. Parasite prevalence is less relevant in areas of low transmission intensity where parasite prevalence rates are less than 5 per cent and more difficult to measure precisely.

GENDER EQUALITY ISSUES

Potential differences between men and women are a function of biological factors and gender roles and relations. Biological factors vary between men and women and influence susceptibility and immunity to tropical diseases. Women’s immunity is particularly compromised during pregnancy, making pregnant women more likely to become infected and implying differential severity of the consequences.

Malaria infection during pregnancy can range from an asymptomatic infection to a severe life-threatening illness depending on the epidemiological setting. In areas of stable malaria transmission most adult women have developed enough natural immunity that infection does not usually result in symptoms, even during pregnancy. In such areas, the main impacts of malaria infection are malaria-related anaemia in the mother, and the presence of parasites in the placenta, which contribute to low birth-weight, a leading cause of impaired development and infant mortality. Malaria during pregnancy is an important cause of maternal mortality. In areas of unstable malaria transmission most women have acquired little immunity to malaria and are thus at risk of severe malaria and death.

Gender roles and relations may influence access to and control of resources needed to protect women and men from being infected. For instance, an unequal balance of power between men and women and an inequitable access to health care and financial resources as a result of gender and other social inequalities lead to a higher vulnerability to malaria and other infectious diseases among women. These inequalities can also affect women’s ability to respond appropriately and access prevention and treatment efforts where available.

In some societies, the activities of men and women during peak biting times may also result in different risks of infection. In particular, men may often have a greater occupational risk of contracting malaria than women if they work in forests at peak biting times, or migrate to areas of high endemicity for work.

DATA FOR GLOBAL AND REGIONAL MONITORING

The World Health Organization (WHO) is the agency responsible for compiling these indicators at the international level. WHO compiles information supplied by national ministries of health, the agencies responsible for malaria surveillance in endemic countries. Population data are derived from projections made by the United Nations Population Division.

Data are adjusted to allow for international comparability. Adjustments are made for underreporting of cases in countries due to patients not using public sector facilities, or gaps in public sector reporting systems and over-diagnosis of malaria in countries that do not undertake laboratory confirmation of cases. Where data from surveillance systems are not available, or are considered to be of insufficient quality, incidence is derived from estimated levels of malaria risk and will mostly be from a different source than locally available estimates.

The methods applied for calculating incidence rates are described fully in the World Malaria Reports 2010 and 2011, together with procedures for estimating the uncertainty around estimates.

The number of malaria deaths is derived by one of two methods:
  • By multiplying the estimated number of Plasmodium falciparum malaria cases in a country by a fixed case-fatality rate. This method is used for all countries outside Africa and for countries in Africa where estimates of case incidence are derived from routine reporting systems, and where malaria comprises less than 5 per cent of all deaths in children under 5.
  • For countries in the African Region where malaria comprises 5 per cent or more of all deaths in children under 5, the number of deaths is derived from an estimate of the number of people living at high, low or no risk of malaria. Malaria death rates for these populations are inferred from longitudinal studies of malaria deaths as described in the Global Burden of Disease: 2004 Update.

FOOTNOTE

SUPPLEMENTARY INFORMATION



EXAMPLES



REFERENCES



KORENROMP E. (2005). Malaria Incidence Estimates At Country Level For The Year 2004. Proposed Estimates and Draft Report. Geneva, World Health Organization. Available from http://www.who.int/malaria/publications/atoz/incidence_estimations2/en/index.html.

ROWE, A.K. et al. (2006). The Burden of Malaria Mortality Among African Children in the Year 2000. International Journal of Epidemiology, 35:691–704. Available from http://ije.oxfordjournals.org/cgi/content/full/35/3/691.

SNOW, R.W. et al. (2003). The Public Health Burden of Plasmodium Falciparum Malaria in Africa: Deriving the Numbers. Bethesda, Maryland, Fogarty International Center, National Institutes of Health. Available from http://www.cdc.gov/malaria/pdf/snow_wp11.pdf.

UNITED NATIONS (2008). World Population Prospects: The 2008 Revision. New York. Available from http://esa.un.org/unpp/.

WORLD HEALTH ORGANIZATION (2008). Global Burden of Disease: 2004 Update. Geneva. Available from http://www.who.int/healthinfo/global_burden_disease/2004_report_update/en/index.html.

WORLD HEALTH ORGANIZATION (2008). World Malaria Report 2008. Geneva. Available from http://www.who.int/malaria/publications/atoz/9789241563697/en/index.html.

WORLD HEALTH ORGANIZATION (2009). World Malaria Report 2009. Geneva. Available from http://www.who.int/malaria/publications/atoz/9789241563901/en/index.html.

WORLD HEALTH ORGANIZATION (2010). World Malaria Report 2010. Geneva. Available from http://www.who.int/malaria/publications/atoz/9789241564106/en/index.html.

WORLD HEALTH ORGANIZATION (2011). World Malaria Report 2011. Geneva. Available from http://www.who.int/malaria/world_malaria_report_2011/en/.

WORLD HEALTH ORGANIZATION (1998). Gender and Health: A Technical Paper. Geneva. Available from http://www.who.int/docstore/gender-and-health/pages/Publications.html.

WORLD HEALTH ORGANIZATION. WHO Fact Sheet on Malaria. Geneva. Internet site http://www.who.int/mediacentre/factsheets/fs094/en/.

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