What Is HIV? Transmission, Symptoms, Testing, and Treatment Explained

HIV (Human Immunodeficiency Virus) is the name of the virus. AIDS (Acquired Immunodeficiency Syndrome), on the other hand, is the state someone is in once HIV has weakened their immune system enough to trigger one of a specific list of illnesses — what MHLW calls "indicator diseases" (MHLW, "HIV and AIDS").

So having HIV doesn't automatically mean you have AIDS. Thanks to how far treatment has come, someone living with HIV can go their whole life without ever developing an indicator disease.

According to UNAIDS's 2025 Fact Sheet, the global HIV/AIDS situation at the end of 2024 was as follows:

Where treatment access stands (2024, UNAIDS/WHO): 87% of people living with HIV know their status, 77% are on treatment, and 73% have an undetectable viral load — progress toward the international "95-95-95" targets.

The trend: Annual AIDS-related deaths have dropped sharply from their 2004 peak of roughly 2.1 million, largely thanks to expanded treatment access. Even so, as of 2024, an estimated 9.2 million people — nearly a quarter of everyone living with HIV worldwide — still are not receiving treatment that can substantially improve health and survival (UN, 2024 data).

According to MHLW's AIDS Surveillance Committee, here are the confirmed 2024 numbers:

The trend: Numbers had been declining since peaking around 2013, but they've ticked back up for two years running — 884 in 2022, 960 in 2023, 994 in 2024. 94.3% of new cases are men. Men who have sex with men (MSM) account for more than half of newly reported HIV cases (63.0%) (MHLW's AIDS Surveillance Committee, 2024 report).

Worth noting: Testing dropped off during the COVID-19 pandemic, which may mean a fair number of asymptomatic infections went undetected starting in 2020 (JIHS).

According to MHLW, there are only three transmission routes:

1. Sexual contact (through mucous membrane contact with semen or vaginal fluid)
2. Blood (shared needles, needle-stick injuries in healthcare settings, etc.)
3. Mother-to-child (during pregnancy, birth, or breastfeeding — though antiretroviral medication can dramatically lower this risk)

Worth knowing: HIV requires specific conditions to transmit, which is why everyday contact — handshakes, baths, sharing dishes or drink cans — simply doesn't spread it (MHLW).

HIV infection generally unfolds in three broad stages (MHLW's HIV Testing & Counseling Map).

① Acute infection (the first few weeks)

Two to six weeks after infection, some people develop flu-like symptoms — fever, swollen lymph nodes, sore throat, rash, muscle aches, headache, diarrhea. MHLW describes this simply as "flu-like symptoms (fever, muscle aches, headache, etc.) that can appear a few weeks after infection." A peer-reviewed review in the American Family Physician puts a number on it: 50–90% of people with acute HIV infection develop some symptoms (Chu C, Selwyn PA. 2010;81(10):1239-1244.). However, these symptoms can look very similar to those of influenza and other infections, so symptoms alone cannot determine whether someone has HIV.

② The asymptomatic period

Most people then go years — often somewhere between several years and over a decade — without any noticeable symptoms. However, HIV remains active in the body, and without treatment, immune function gradually declines as CD4 cell counts decrease.

③ Progression to AIDS

Once the immune system is weakened enough, opportunistic infections — illnesses a healthy immune system would normally fend off — start to appear. If someone meets the diagnostic criteria for one of the officially defined indicator diseases, that's when a diagnosis of AIDS is made.

AIDS is diagnosed once someone with HIV develops one of 23 conditions defined by MHLW as "indicator diseases." Under Japan's Infectious Diseases Control Law, a case must be reported once at least one of these is clearly present.

A note on this list: This is compiled from MHLW's reporting criteria and materials published by JIHS. Each condition actually comes with more detailed diagnostic criteria — specific sites, severity thresholds, and so on — which we've simplified here for readability. If you need the precise clinical criteria, check MHLW's reporting-standards page directly.

Current medicine can't fully clear HIV from the body. What it can do is suppress the virus to undetectable levels through antiretroviral therapy (ART), letting people live long, healthy lives.

According to JIHS's 2024 report, 33.4% of new 2024 diagnoses (32.8% among Japanese nationals) were already at the AIDS stage by the time they were diagnosed — in other words, the person had been living with undiagnosed HIV long enough for it to progress. Catching it earlier remains one of the biggest challenges.

U=U stands for Undetectable = Untransmittable.

Here's MHLW's own explanation:

A person living with HIV whose viral load has been suppressed below the detectable threshold for at least six consecutive months, through consistent treatment, cannot transmit HIV to others through sex.

This isn't a hopeful slogan — it's a well-established scientific fact, and one that matters for cutting through the stigma and misunderstanding people living with HIV still face. Globally, UNAIDS has been pushing the U=U message since 2016.

• Use condoms during sex
• Get tested regularly, especially if you're sexually active with new or multiple partners
• Don't share needles or syringes
• Consider HIV prevention medication (PrEP and PEP)

There are two medication-based approaches to HIV prevention: PrEP (pre-exposure prophylaxis), and PEP (post-exposure prophylaxis), taken as emergency treatment after a possible exposure.

PrEP (pre-exposure prophylaxis)

• Taken before potential exposure to HIV to reduce the risk of infection
• On August 28, 2024, the antiretroviral drug Truvada received Japan's first-ever drug approval for use as PrEP (Nikkei Medical)
• When used specifically for PrEP, it's not covered by public health insurance and is billed as out-of-pocket care

PEP (post-exposure prophylaxis)

• Taken as an emergency measure after a potential exposure to HIV — for example, if a condom breaks during sex
• Needs to start as soon as possible, and no later than 72 hours after exposure
• Involves 28 days of combination antiretroviral medication
• PEP is not covered by public health insurance and is provided as out-of-pocket care. Access is limited, so it is important to seek medical advice as soon as possible (JIHS's AIDS Clinical Center (ACC))

If your partner is living with HIV: as long as they've maintained an undetectable viral load through treatment (U=U), there's no risk of transmission through sex.

Understanding the testing window

Right after infection, there's a stretch of time when a blood test can come back negative even though someone is infected. That's the "window period" (MHLW's "HIV Testing Basics").

*A note on this: the recommendation to retest at three months is something you'll find consistently referenced on MHLW's own "HIV Testing & Counseling Map" (window periods vary from person to person, and it typically takes 1–3 months for antibodies to build up to detectable levels — hence the conservative three-month benchmark).

How testing actually works

HIV testing happens in two stages (MHLW's "HIV Testing Basics"):

1. Screening test: If the screening test is negative, the result is reported as negative. However, depending on when the test was taken relative to potential exposure, repeat testing may be recommended because of the window period
2. Confirmatory test: Run if the screening test comes back positive. Screening tests can produce false positives, so a confirmatory test is always required before anyone is actually diagnosed

Where you can get tested

• Public health centers and designated testing sites: Free and anonymous — no name required. You can test at a center outside your home area, too (MHLW's "HIV Testing & Counseling Map")
• Medical clinics: Available through internal medicine, urology, gynecology, or infectious disease departments (fee applies)

Booking a test or talking to someone

• HIV Testing & Counseling Map: Search for free, anonymous testing near you — some locations offer evening/weekend hours or women-only testing days
• Your local public health center: You can also reach out directly. Many municipalities offer anonymous testing with no name or contact information required
• Japan Foundation for AIDS Prevention hotline: Toll-free at 0120-177-812 (03-5259-1815 from a mobile phone). Weekdays 10am–1pm and 2pm–5pm, closed on holidays and over New Year's. Trained counselors take your call directly (JFAP)

You don't have to figure this out alone — getting tested is the first step toward protecting both yourself and the people you care about.