Thursday, 7 June 2018

Epidemiology of HIV and AIDS

The human immunodeficiency virus (HIV) kills or impairs the cells of the immune system and progressively destroys the body’s ability to protect itself. Over time, a person with a deficient immune system (immunodeficiency) may become vulnerable to infections by disease-causing organisms such as bacteria or viruses. These infections can become life threatening.

Mechanism of HIV Infection
HIV enters the bloodstream and seeks out T-helper lymphocytes, white blood cells essential to the functioning of the immune system. One of the functions of these cells is to regulate the immune response in the event of attack from disease-causing organisms such as bacteria or viruses. When the virus infects the T-helper lymphocyte, the cell sends signals to other cells, which produce antibodies. This T-helper lymphocyte cell may also be called the T4 or the CD4 cell.
HIV infects and destroys the T-helper lymphocytes and damages their ability to signal for antibody production. This results in the eventual decline of the immune system.
There are five stages of HIV/AIDS infection:
·         Primary or acute infection
·         The window period ending with seroconversion
·         The asymptomatic period
·         The period of being symptomatic
·         Full-blown AIDS
 The Origin of HIV
Since the human immunodeficiency virus was identified in 1983, researchers have worked to pinpoint the origin of the virus. In 1999 an international team of researchers reported that they discovered the origins of HIV-1, the predominant strain of HIV in the developed world.
A subspecies of chimpanzees native to West Equatorial Africa was identified as the original source of the virus. The researchers believe that HIV-1 was introduced into the human population when hunters became exposed to infected blood. The transmission of HIV is driven by changes in migration, housing, travel, sexual practices, drug use, war, and economics that affect both Africa and the entire world.
HIV Strains and Subtypes
HIV has divided into two primary strains: HIV-1 and HIV-2. Worldwide, the predominant virus is HIV-1, and generally when people refer to HIV without specifying the type of virus they are referring to HIV-1. The relatively uncommon HIV-2 type is concentrated in West Africa and is rarely found elsewhere.
HIV is a highly variable virus that mutates very readily. This means there are many different strains of HIV, even within the body of a single infected person. Based on genetic similarities, the numerous virus strains may be classified into types, groups, and subtypes.
Both HIV-1 and HIV-2 have several subtypes. It is virtually certain that more undiscovered subtypes are in existence now. It is also probable that more HIV subtypes will evolve in the future. As of 2001, blood testing in the United States can detect both strains and all known subtypes of HIV.
Epidemiology of HIV and AIDS
Epidemiology is the study of how disease is distributed in populations and of the factors that influence or determine this distribution. Epidemiologists try to discover why a disease develops in some people and not in others. Clinically, AIDS was first recognized in the United States in 1981. In Washington State, the first case of AIDS also appeared in 1981. But it wasn't until 1983 that the virus was identified as the cause of the new disease. Since then, the number of AIDS cases has continued to increase, both in the United States and in other countries. 
People who are infected with HIV come from all races, countries, sexual orientations, genders, and income levels. Globally, most of the people who are infected with HIV have not been tested and are unaware that they are living with the virus. The U.S. Centers for Disease Control and Prevention (CDC) estimates that 1.2 million people aged 13 years and older are living with HIV infection, including 168,000 (14%) who are unaware of their infection. This is a decline from 25% in 2003 and 20% in 2012 and is a positive sign because studies have shown that many people with HIV who know that they are infected avoid behaviours that spread infection to others, and they can get medical care and take antiviral medications that may reduce HIV spread by as much as 96% (CDC, 2014; 2014b).
CDC estimates that that there are only 4 transmissions per year for every 100 people living with HIV in the United States, which means that the clear majority (at least 95%) of people living with HIV do not transmit the virus to anyone else. This represents an 89% decline in the transmission rate since the mid-1980s, reflecting the combined impact of testing, prevention counselling, and treatment efforts targeted to those living with HIV infection (UNAIDS, 2013).
The estimated incidence of HIV has remained stable overall in recent years, at about 50,000 new HIV infections per year (CDC, 2014b). While this is still too high a level, stabilization is a sign of progress. With continued increases in the number of people living with HIV thanks to effective HIV medications, there are more opportunities for HIV transmission than ever before. Yet, the annual number of new infections has not increased (UNAIDS, 2013).
Worldwide, there were about 2.1 million new cases of HIV in 2013, and about 35 million people are living with HIV around the world. Of those, 3.2 million are children, 2.1 million are adolescents, and 4.2 million are people over age 50. In 2013 new HIV infections worldwide were 2.1 million, but new infections have fallen 38% since 2001 and new infections among children have fallen by 58% in the same period (CDC, 2014a; UNAIDS, 2014).
Through 2011 the cumulative estimated number of deaths of people with diagnosed HIV infection ever classified as stage 3 (AIDS) in the United States was 648,459 (deaths may be due to any cause, which can make data interpretation complex). Nearly 39 million people with AIDS have died worldwide since the epidemic began (CDC, 2014a).
Globally, AIDS-related deaths, which peaked in 2005 at 2.4 million, have declined steadily ever since, and were estimated at 1.5 million in 2013 (UNAIDS, 2014). Even though Sub-Saharan Africa bears the biggest burden of HIV/AIDS, countries in South and Southeast Asia, Eastern Europe and Central Asia, and those in Latin America are significantly affected by HIV and AIDS (CDC, 2014a; UNAIDS, 2014).
The discovery of combination antiviral drug therapies in 1996 resulted in a dramatic decrease in the number of deaths due to AIDS among people given the drug therapies. Many people who have access to the therapies may not benefit from them or may not be able to tolerate the side effects. The medications are expensive and require strict dosing schedules. In developing countries many people with HIV have no access to the newer drug therapies.
During the period 2008–2013, men accounted for 85% of the new cases and women for 15%. Fifty-seven percent were white, 17% black, 16% Hispanic, and 5% Asian. The remaining 5% included native Hawaiians, American Indians, and those of multiple race. Children under 13 accounted for 2% of the new cases, while those age 13 to 24 were another 14%. Most of the cases (57%) were among adults 35 to 54, and the remaining 28% were age 54 and older (WDOH, 2014).

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