The term “patient zero” generally refers to a person identified as the initial carrier of an infectious disease in an outbreak of related cases. It is difficult to identify patient zero in the case of HIV, as many individuals may have carried the infection before doctors understood the disease.

For many years, one man was named patient zero and incorrectly blamed for spreading HIV across the United States. However, more recent evidence has determined that HIV was present in the U.S. before this time. This individual was simply one of the thousands who contracted the virus early on in the epidemic.

Keep reading to learn more about HIV patient zero and what we know about the origins of this virus.

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HIV is a virus that attacks and weakens the body’s immune system. Therefore, individuals living with HIV are more susceptible to other diseases and infections.

HIV spreads through contact with an infected person’s bodily fluids. The two most common ways it spreads are through having unprotected sex and sharing injection drug equipment.

If left untreated, HIV continues to damage the immune system, and over time it can lead to a syndrome called AIDS. If an individual has AIDS, their immune system is badly damaged, and they are at high risk of life threatening infections.

However, not every HIV-positive person develops AIDS because taking daily HIV medication prevents the disease from progressing to that point.

Learn more about HIV and AIDS here.

HIV was first identified in 1981 and is the cause of one of the most deadly and persistent epidemics in human history.

The identification of the virus began with rare lung infections and rare and unusually aggressive cancers in young gay men in New York and California. By December 1981, doctors found these same symptoms in five infants whose mothers were drug users and sex workers.

By 1982, AIDS became the focus of Congress. Experts estimated that tens of thousands of people might have already contracted HIV. However, Congress did not approve the first dedicated funding for AIDS research and treatment until mid-1983.

In 1992, AIDS became the number one cause of death for men in the U.S. aged 25–44. By 1995, there were 500,000 reported cases of AIDS in the country. However, in 1996 the number of new AIDS cases declined for the first time since the epidemic began.

The first verified case of HIV derives from a 1959 blood sample of an individual who lived in the Democratic Republic of Congo. However, scientists cannot say whether this person was the first human with HIV, or the first documented case, known as patient zero.

There are numerous documented cases before this one in which the patterns surrounding death suggest HIV as the cause. However, there is no way to prove this through a blood sample. The 1959 sample is the first recorded case in which a blood sample can confirm HIV infection but may not be the first official emergence of HIV.

For many years, Gaétan Dugas was presumed patient zero in the U.S., originally termed patient O for “outside Southern California.” He was a flight attendant suspected of picking up HIV in Africa or Haiti and bringing it back to the U.S., transmitting it to dozens of men before his death.

However, an analysis into genetics in 2016 found that the viral strain Dugas had was already spreading among men in New York before he began visiting the city’s gay bars. This means that Dugas was not the initial individual with HIV. It seems he was an early case but was by no means the first.

There is limited actual knowledge on how the epidemic entered the U.S. because of the challenges in tracing HIV to one individual.

Scientists determined that HIV resembles the Simian Immunodeficiency Virus (SIV), a virus that attacks the immune system of apes and monkeys.

In 1999 researchers discovered a chimpanzee with an SIV strain that closely mirrored HIV in humans. They also concluded that chimpanzees were the source of HIV, and the virus crossed from chimpanzees to humans at some point.

As for how the virus spread from chimps to humans, scientists postulate that someone killed and ate a chimp, or the chimp’s blood got into the cuts or wounds of the human while hunting. Once in contact with the human body, the virus adapted and became HIV.

One of the primary challenges experts have in tracking a virus to the initial infection is that it may present as another infection. For example, when HIV first appeared in the U.S., doctors reported rare lung infections in a group of individuals.

Because of this, doctors may never identify cases as being due to HIV. People may have had HIV before these individuals, but received a diagnosis for another condition or did not seek medical attention.

Even then, if doctors determine that someone has HIV, it is challenging to identify who had the virus first because of the speed at which it spreads.

It is valuable for scientists to understand the origins of a virus to obtain the following information:

  • what kind of virus it is
  • if it is novel
  • if it represents the emergence of a pathogen that is already known
  • the mode of transmission
  • the host of the virus
  • how many introductions to humans there have been
  • how it connects to previous events
  • if there is evidence for local adaptation

In some cases, an emergent virus is a variation of an existing virus, such as the SARS-CoV-2 coronavirus that causes COVID-19. This knowledge allows for the rapid development of treatments and vaccines as experts already understand the mechanics of similar viruses.

Understanding the origin of a virus makes it possible to determine how it transmits from one animal or person to another. Not only does this help scientists develop treatments, but they can also work on methods to prevent its spread.

HIV is a virus that attacks and damages the immune system. When left untreated, it can progress to AIDS, a life threatening condition.

HIV first appeared in the United States in the early 1980s and quickly escalated in numbers until 1996, when new cases declined for the first time.

HIV originated from the virus SIV, which infects chimpanzees. Once it found a human host, it adapted into HIV.

The first documented case of HIV with a verified blood sample occurred in 1959 in the Dominican Republic of Congo. However, scientists cannot say if this was the first occurrence of HIV or only the first recorded case.