Disease Incidence, Prevalence and Disability
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Part 3 Disease incidence, prevalence and disability 9. How many people become sick each year? 28 10. Cancer incidence by site and region 29 11. How many people are sick at any given time? 31 12. Prevalence of moderate and severe disability 31 13. Leading causes of years lost due to disability in 2004 36 World Health Organization 9. How many people become sick each such as diarrhoeal disease or malaria, it is common year? for individuals to be infected repeatedly and have several episodes. For such conditions, the number The “incidence” of a condition is the number of new given in the table is the number of disease episodes, cases in a period of time – usually one year (Table 5). rather than the number of individuals affected. For most conditions in this table, the figure given is It is important to remember that the incidence of the number of individuals who developed the illness a disease or condition measures how many people or problem in 2004. However, for some conditions, are affected by it for the first time over a period of Table 5: Incidence (millions) of selected conditions by WHO region, 2004 Eastern The Mediter- South- Western World Africa Americas ranean Europe East Asia Pacific Tuberculosisa 7.8 1.4 0.4 0.6 0.6 2.8 2.1 HIV infectiona 2.8 1.9 0.2 0.1 0.2 0.2 0.1 Diarrhoeal diseaseb 4 620.4 912.9 543.1 424.9 207.1 1 276.5 1 255.9 Pertussisb 18.4 5.2 1.2 1.6 0.7 7.5 2.1 Measlesa 27.1 5.3 0.0e 1.0 0.2 17.4 3.3 Tetanusa 0.3 0.1 0.0 0.1 0.0 0.1 0.0 Meningitisb 0.7 0.3 0.1 0.1 0.0 0.2 0.1 Malariab 241.3 203.9 2.9 8.6 0.0 23.3 2.7 Dengueb 9.0 0.1 1.4 0.5 0.0 4.6 2.3 Lower respiratory infectionsb 429.2 131.3 45.4 52.7 19.0 134.6 46.2 Complications of pregnancy: – maternal haemorrhage 12.0 3.0 1.2 1.6 0.7 4.0 1.4 – maternal sepsis 5.2 1.2 0.6 0.7 0.3 1.7 0.6 – hypertensive disorders 8.4 2.1 0.8 1.2 0.5 2.8 1.1 – obstructed labour 4.0 1.1 0.1 0.5 0.0 1.9 0.4 – unsafe abortion 20.4 4.8 4.0 2.9 0.5 7.4 0.8 Malignant neoplasms – all sites 11.4 0.7 2.3 0.5 3.1 1.7 3.2 Congestive heart failurec 5.7 0.5 0.8 0.4 1.3 1.4 1.3 Stroke, first-ever 9.0 0.7 0.9 0.4 2.0 1.8 3.3 Injuriesd due to: – road traffic accidents 24.3 4.7 2.2 2.8 1.8 8.6 4.1 – falls 37.3 2.8 3.3 3.6 5.3 14.4 8.0 – fires 10.9 1.7 0.3 1.5 0.8 5.9 0.7 – violence 17.2 4.5 5.9 2.0 1.6 2.2 1.0 a New cases. b Episodes of illness. c Incidence of congestive heart failure due to rheumatic heart disease, hypertensive heart disease, ischaemic heart disease or inflammatory heart diseases. d Incidence of injuries severe enough to require medical attention. e An entry of 0.0 in the table refers to an incidence of less than 0.05 million (less than 50 000). 28 Part 3 Global Burden of Disease 2004 time (mostly one year). Incidence does not meas- by breast cancer, then colon and rectum cancer, ure how many people have a disease at any given and stomach cancer. Lung cancer is also the lead- 1 moment (this is “prevalence”) or how badly their ing cancer in the Western Pacific Region, but is less lives are affected. A health problem or disease can common than colon and rectum cancers or breast have a relatively low incidence but cause death or cancers in most other regions. Cervix cancer is the disability, and will therefore result in a high burden cancer with the highest incidence in the African and 2 of disease or many life years lost. Conversely, some South-East Asia regions, even though it occurs only common illnesses may cause a much smaller burden in women. of disease or fewer life years lost. Data on the con- Variations across regions in the risk of cancer are tribution of various conditions and diseases to the best shown using age-standardized incidence rates 3 burden of disease in a community are given in later that apply the estimated age- and sex-specific inci- sections. dence rates for cancers in each region to the WHO World Standard Population (22). This estimates how Diarrhoeal disease is the most common cause of many cases of cancer would occur in that population 4 illness if it experienced the cancer incidence rates of a given region (Figure 18). Of the diseases listed in Table 5, diarrhoeal disease Annex A affects far more individuals than any other illness, even in regions that include high-income countries. Pneumonia and other lower respiratory tract infec- tions are the second most common cause of illness Annex B globally, and in all regions except Africa. Other common illnesses – such as upper respiratory tract infections (including the common cold) and aller- Annex C gic rhinitis (hay fever) – have not been included in Table 5. References 10. Cancer incidence by site and region 11.4 million people were diagnosed with cancer in 2004 More cancers occur in high-income countries than in low- and middle-income countries. Cervix can- cer is the only type of cancer more common in the African and South-East Asia regions than in high- income countries. In part, this is due to the age of the populations in different regions, because most cancers affect older adults; also, some cancers, such as prostate cancer, are much more common in older men than in younger men. Another factor contrib- uting to the distribution of a type of cancer is the number of people exposed to causes, such as ciga- rette smoking in the case of lung cancer, and hepati- tis B virus in the case of liver cancer. Globally, lung cancer is the most common cancer (Table 6), followed Disease incidence, prevalence and disability 29 World Health Organization Table 6 : Cancer incidence (thousands) by site, by WHO region, 2004 Eastern The Mediter- South- Western World Africa Americas ranean Europe East Asia Pacific Lung cancer 1 448 27 264 34 401 164 558 Stomach cancer 933 38 89 25 182 78 521 Colon and rectum cancers 1 080 32 217 23 409 106 293 Liver cancer 632 65 38 13 67 64 386 Cervix cancer 489 95 95 15 81 180 73 Breast cancer 1 100 72 310 54 326 154 184 Prostate cancer 605 77 236 13 180 45 54 Lymphomas and multiple 479 56 102 39 113 91 79 myeloma Leukaemia 375 20 68 28 86 72 101 Other cancers 5 187 234 874 226 1 214 773 919 All sites (excluding non- 11 474 716 2 294 470 3 058 1 726 3 166 melanoma skin cancer) Figure 18: Age-standardized incidence rates for cancers by WHO region, 2004 High income Africa Lung Breast Americas Colon, rectum, stomach oesophagus Eastern Mediterranean Liver, pancreas Prostate Europe Cervix, uterus, ovary Lymphomas, multiple myeloma, leukaemia South-East Asia Other malignant neoplasms Western Pacic 0 50 100 150 200 250 300 Age-standardized incidence per 100 000 population 30 Part 3 Global Burden of Disease 2004 11. How many people are sick at any as a synonym or proxy for “loss of health”. However, given time? the GBD uses the term disability to refer to loss of 1 health, where health is conceptualized in terms of The prevalence of an illness or condition is the functioning capacity in a set of health domains such number of individuals who have the condition at as mobility, cognition, hearing and vision. any moment. In some cases, such as epilepsy or The original GBD study established severity 2 migraine, individuals will not have symptoms most weights for approximately 500 disabling sequelae of the time, but still have the condition. The effects of diseases and injury, in a formal study involving of the illness and the loss of health will vary from health workers from all regions of the world. These one individual to another. The result may be serious weights were then grouped into seven classes, where 3 impairments and disability affecting a person’s abil- class I has a weight between 0 and 0.02, and class ity to work or take part in family and community VII a weight between 0.7 and 1 (Table 8). Participants activities, or only mild impairments or disability. in the study estimated distributions across the seven Prevalence data therefore do not capture the burden classes for each sequela. Distributions across disabil- 4 of disease experienced by individuals in terms of lost ity classes were estimated separately for treated and health. untreated cases where relevant; distributions could also vary by age group and sex. Annex A Anaemia, hearing loss and migraine are the three These distributions were applied to prevalence most prevalent conditions estimates from the GBD 2004 study to estimate the prevalence of disability by severity class in 2004.