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The Window Period

The “Window Period” (a.k.a. Seroconversion Time or Diagnostic Period) is the time that the body takes to produce measurable amounts of antibodies after infection. Therefore if an HIV antibody test is taken during the window period, it will be negative since antibodies are not yet present at a detectable level. However, the infected person may transmit HIV to others during that period.

People taking the test are advised if the result is negative, to return for follow-up testing in 3 months by which time antibodies may be detected to confirm infection. They are also encouraged to avoid risk behaviors during the 3 months. In HCV the window period is even longer.

The window period is applicable to all diagnostic methods. It can be up to a year:

HIV: 30–90 days (1–3 months)
HCV: 70–180 days (2.5–6 months)

During the window period infected people may not be detectable.
After this period, the vast majority of infected people are detectable

2.1 The Window Period and the Different Test Methods
All the different diagnostic tests are related to the ELISA. These other methods’ results are measured by number of days before seroconversion (when the body produces measurable amounts of antibodies):

PCR/NAT – can shorten the window period by 10–12 days
Antigen Tests (p24) – can shorten the window period by week or so

However, these still leave an unknown and unacceptably long period during which “tested negative” people or blood products are “unknowingly” infecting others, spreading the infection/epidemic faster.

Window Period – Problem Issues:

2.2.1 HIV
In the window period:

Impossible to contain the epidemics, since antibody negative-tested people may carry the virus and not know they have it. False-negative (window period) people do not take precautions or listen to preventive guidelines.

Epidemiological factor—each HIV carrier can infect 50 people each year.

People that may infect should repeat the HIV test. Infection of embryos/new-born babies from unknowingly infected mother will not get the right prevention treatment, thus may later get AIDS or will carry the virus.

Anti retroviral treatment of the mother (and the baby) reduces mother-to-child transmission of HIV from 25-30% to 1-2%. When infections are detected late, injuries to medical staff may infect other patients and other staff members.

Early treatment could cure the staff and prevent spreading the disease. Incomplete detection of infectious blood units (and blood products) can transmit the infection to multiple recipients. Fear and suffering of affected individuals due to a long uncertainty period (3 months) from suspected exposure time/incidence. Impossible to provide early treatment that would reduce overall treatment to less than 8 years.

High-risk population for example prisoners. Almost impossible to prevent the spread of HIV inside the prison, and outside when prisoners are taking vacation, even if only a few carriers remain undetected (Thailand prisoners study – Klong Prem Central Prison, Bangkok, found that 25% of prisoners who agreed to be tested were HIV positive, compared with a general prevalence of 1.5% in the national population).

Drug users may use infected needles and syringes, and will not take precautions Candidate and new army and police recruits cannot get final approval until it is proved that they are not carrying the virus(es). Injuries to medical staff may infect patients and other staff members. Early treatment could cure the staff and prevent spreading the disease. The window period causes delay in developing vaccines for HIV.

2.2.2 HCV
In the window period:

Impossible to contain the epidemic, since negative-tested people may carry the virus and infect others, via blood transfusions, etc. exposing more and more people to the epidemic. HCV detection problem: a liver biopsy may be the only way to detect HCV