# Presentation: 174869

## HIV Incidence Testing for Surveillance

- Bharat S. Parekh, Ph.D.
- CDC, Atlanta

## Nseronegative

- Nseronegative

- Nseronegative

- Nseropositive

- Nincident

- Nincident

- FNincident

- 1 year

- prospective

- Cross-sectional

- Cross-sectional verses Longitudinal Incidence Measurement

## The Ideal Assay for Recent Infection

- Describes a distinct interval of relatively uniform duration
- Is universally positive in recent infection and negative later in infection (or vice versa)
- Is unaffected by:
- virus subtype
- mode of transmission
- therapy
- OI and AIDS
- Age, sex, race
- Has a relatively long window, all else being equal

## Early HIV Infection

- RNA+ Ab-

- P24+ Ab -

**Seroconversion to Ab cutoff**

- RNA

- p24

- Ab

- seroconversion

- Antibody cutoff
-   Quantity
-   Proportion
-   Avidity
-   Isotype
-   specificity

- days

- Response

**infection**

## Assays for Recent HIV Infection

| Assay | Test for: | window |       Interval |   |
| --- | --- | --- | --- | --- |
|   |   | from: | to: | duration: |
| HIV RNA | Plasma RNA | RNA + | seroconversion | 19 days |
| HIV p24 | Plasma p24 | p24+ | seroconversion | 14 days |
| STARHS | HIV Ab titer | seroconversion | titer cutoff | 130-170 days |
| BED-CEIA | HIV Ab/total IgG | seroconversion | Ab proportion cutoff | 153 days |
| Avidity | HIV Ab avidity | seroconversion | avidity cutoff | variable |
| Affinity | HIV Ab affinity | seroconversion | affinity cutoff | variable |
| IgG3 isotype | IgG3 anti-p24 Ab | seroconversion | undetectable IgG3 Ab | undetermined |
| anti-HIV p31 | anti-HIV integrase | seroconversion | detection of anti-p31 | 70 days |

## BED-CEIA Window periods

_**Subtypes**__**	**__**	**__**Country **__**	**__**Window (95% CI)**_
- AD 			Kenya                  171 (150-199)
- B     			Amsterdam          127 (113-152)
- B     			Thailand              143 (118-170)
- C     			Zimbabwe/Ethi     181 (165-198)
- E           		Thailand              115 (106-125)
**OVERALL****	****	****	****                  153 (146-165)**

## Incidence formula *

- Incidence

- =

- (365/window period) X (# who test incident)

- # at risk

- X   100

- I   =

- (365/*w) x *Nincident

- Nseronegative+

- (365/*w) x *Nincident/2

- X   100

- * Assumes constant incidence +/- 1 year

## Janssen (1998)

- Incidence =

- 	 Nincident    	         365
- (Nincident+Nseronegative)    W

- x            x100

_*Important Numbers:*_
- Nseroneg  = Number Seronegative
- Nincident  = Number Recently infected
- W = window period

- Expressed as = Incidence per 100 persons per year

## Validation of assay performance using longitudinal cohort studies

- Choose a population with conventional measure of incidence
- Test positives collected during certain time-periods by the incidence assay
- Calculate incidence and compare to observed incidence

## Summary of BED assay validation in prospective observational cohorts

| Study | Person-years followup | Number of Seroconverters |  | Annualized incidence/100 p-y |  |
| --- | --- | --- | --- | --- | --- |
|  |  | Observed | BED-
Estimated | Observed (CI) | BED-estimated (CI) |
| A | 1126 | 14 | 12 | 1.24
(0.6-1.9) | 1.10
(0.28-1.9) |
| B | 9999 | 349 | 345 | 3.49
(3.13-3.9) | 3.45
(2.6-4.3) |
| C | 1844 | 120 | 108 | 6.51
(5.4-7.6) | 5.85
(3.9-7.8) |

## Application of incidence tests to surveillance settings

- Comparison between different populations
- Demographic correlates of high and low incidence in a population
- Comparison of incidence over time in the same population
- Extrapolations to National incidence estimates.

## Incidence implementationEpidemiology

- Protocol development
- Site selection
- Population selection
- Statistical power projections
- Data management (epi/lab)

## Incidence implementationLaboratory

- Identify the lab (central) and personnel
- Hands-on training of personnel
- Acquisition of equipments/supplies
- Performance evaluation by CDC
- QA/QC Guidance
- Specimen collection, storage, and transport mechanism
- Data Management
- Proficiency Testing

## Analysis

- Merge epi and lab data
- Incidence calculation
- Post-test adjustments
- Extrapolation/trend
- Statistical analysis
- Summation
- Dissemination

## Inappropriate Specimens for Incidence Surveillance

- False positives (appropriate algorithm    for surveillance?)
- HIV-2
- Improper storage/transport
- Specimens stored at 4o C for extended period
- Contaminated specimens
- Hemolyzed specimens

## Inappropriate Specimens for Incidence Surveillance

- False positives (appropriate algorithm    for surveillance?)
- HIV-2
- Improper storage/transport
- Specimens stored at 4o C for extended period
- Contaminated specimens
- Hemolyzed specimens

- ?

- }

## Sort the specimens by Final OD-n

## Confirm HIV Serology for all with OD-n <0.3

## Corrections

- Remove negatives and HIV-2 specimens from analysis
- Reduce number recently infected
- Increase number of seronegatives
- If all seropositives are not tested?
- E.g. 20% of seropositives are not tested
- Reduce the number of seronegatives by 20%

## Ensuring Quality of TestingInitial versus Confirmatory plot

## Take-Home Messages

- Trained laboratory personnel in the incidence assay, data management and QA/QC
- Laboratory with needed equipment and supplies [e.g. incubators (37 C and 25 C), multichannel pipettes, p20 etc]
- Surveillance sites trained for specimen collection, processing, storage and transport
- Testing algorithm in place to identify HIV-1 seropositives correctly (correct prevalence)
- Monitor testing quality>ongoing activity
- Appropriate epidemiolgic support
- Hot-line >> bparekh@cdc.gov for lab issues

## Cambodia Sentinel Surveillance

- Positive specimens from 3 years: 1999, 2000 & 2002 (total N=3590)
- 4 specific populations
- ANC, CSW, IDSW and Police
- Tested at UCLA (Dr. Vonthanak, Fogarty Fellow from Cambodia)

## HIV-1 incidence trends in specific risk groupsCambodia

## Regional Differences in IncidenceCSW - Cambodia

- Regional Differences in Incidence*CSW - Cambodia*