Example of Bias Matched Case-Control Study

Lakkana Thaikruea

MD., Cert of FETP, M.S., PhD.Department of Community Medicine, Faculty of Medicine, CMU

Risk Factors for Hepatitis C Virus infection Risk Factors for Hepatitis C Virus infection among Blood Donors in Northern Thailandamong Blood Donors in Northern Thailand

Lakkana Thaikruea 1,

Satawat Thongsawat 1,

Niwat Maneekarn 1,

David L. Thomas 2,

Dale Netski 2,

Kenrad E. Nelson 2, 1 Departments of Community Medicine, Medicine, and Microbiology, Chiang Mai University, Chiang Mai, Thailand

2 Departments of Epidemiology & Medicine, Johns Hopkins University, Baltimore, USA

Rationale No effective program in Thailand to prevent HCV

infection Lack of information of majors route of

transmission Distribution of HCV genotypes are not well

understood Researchers from JHU and Chiang Mai

University have conducted study about epidemiology of HCV in northern Thailand

Blood donor is one of the study population besides drug users, patients, and commercial sex workers

This present study focuses on blood donor

Specific aimsSpecific aims

Blood donors in northern Thailand

1. To investigate the potential risk factors

for HCV infection

2. To determine HCV genotype distribution

3. To investigate relationship between HCV

genotype distribution and the routes of

transmission

Features of hepatitis C virus infection

Resolve 15--

Stable 68--

Stable 13---

M ortality 4

Cirrhosis 17

Chronic 85

100--

15% 85%

80% 20%

75% 25%

Background: Route of transmission USA:

IDU1, sex with an IDU,

blood transfusion among non-IDU REDS2:**

male, black, 30 to 49 years,

< high school diploma,

first /only time blood donor,

blood transfusion history1 Injection drug users ; 2 Retrovirus Epidemiology Donor Study

Specific aim 1Specific aim 1

To investigate the potential risk factors for HCV infection among blood donors in

northern Thailand

Methods: Specific aim 1

Setting Design Data collection Data analysis

Study settingStudy setting

Faculty of Medicine, CMU The Blood Bank

- The Maharaj Nakorn Chiang Mai hospital- 1,800-bed capacity and the main referral center

Blood donors- January 2001 - June 2002- ≥ 18 years old at the time of donation/ recruitment- Reside in the north- Donation sites: walk-in and mobile unit

Methods (cont.)

Study design: Specific aim 1Study design: Specific aim 1

Single masked matched case- control Matched variables:

age, gender, donation date, donation sites

Mask: interviewers and physicians did not know HCV status of the participants

Methods (cont.)

Data collection

Invitation letters: 2nd letter in 2 weeks apart Non-participants: sent their participation forms

indicating their unwillingness Enrolment: explain, consent form Trained health personnel of the same gender: face-to-

face interview Physical examination Counseling Laboratory tests: 30 ml blood

– HCV antibodies; EIA-3, RIBA-3– HCV RNA: RT-PCR– HCV genotypes: direct sequencing– Serum ALT

Eligible Case: blood bank EIA-3 positive

Data collection (cont)

PCR positive, or PCR negative with RIBA-3 positive, or PCR negative with both

– positive high cut-off repeat EIA-3 (Abbot)– positive high cut-off repeat EIA-3 (Ortho)

Eligible cases were defined as “confirmed cases ”

If they were HCV EIA-3 positive in blood bank screening and had any of the following:

Data collection (cont.)

Randomly selection: – 1 – 4 eligible controls per case

Matched variables: – ± 15 days of case’s donation date – Age ± 5 years old– Same gender– Same donation sites

Enrolment: same Control:

– Negative to both screening EIA-3 and repeat EIA-3

Eligible Control: blood bank EIA-3 negative

Data collection (cont.)

Spouses of cases and matched controls– Regular sexual relations with the donor

for ≥ 3 months – ≥ 18 years old at the time of recruitment

Enrolment: same HCV infection:

– EIA-3 positive and– Either PCR or RIBA-3 positive

SPOUSES

Flow of matched case-control study Flow of matched case-control study

102 low cut-off EIA-3 positive28 not eligible EIA-3 positive

665 participants

411 matched controls

329 matched controls

254 eligible cases

175 confirmed cases

166 confirmed cases

38,340 donors

372 EIA-3 pos Eligible cases

372 eligible cases 1234 eligible matched controls 618 non-responders

85 returned letters 903 responders

238 non-participants

67 false positive cases12 RIBA-3 indeterminate

82 matched controls

9 cases without control

Participation

Compared between participants and non-participants

Cases: 254 participants (91.4%) versus 24 non-participants

– No statistically significant different Controls:411 participants (65.8%) versus

214 non-participants

– Participants: age in years 33.2 ( VS 31.0)* – Participants: ever donated 81.6 % (VS 61.3 %)*

* P value < 0.05

Data analysis: Specific aim 1 Univariate analysis

– Matched odds ratio (OR) with 95% confidence interval (95% CI) Multivariate analysis

– Conditional logistic regression – Step-wise selection:

• alpha levels of 0.05 for entry and 0.0501 for remove • to guide the selection of variables

– Either independent variables that were likely confounders or had biological importance were forced in to the preliminary model regardless of their statistical significance

Phylogenic analysis 1

– Tree was constructed from nucleic acid sequence alignments using Neighbor joining method

– Sequence alignments were randomly permuted 1,000 times• CONSENSE provided bootstrap values

– Reference sequences: GenBank 1 programs: Gofasta1.1, BioEdit 5.9, Tree View 1.6 , PHYLIP 3.572c package ( SEQBOOT, DNADIST,

NEIGHBOR, CONSENSE)

Results: Specific Aim 1

Demographic distribution Multivariate Spouses

Limitations: Specific aim 1

Limitations:

- causal relationship; temporal ambiguity

- spouses; might not represent

Strengths: Specific aim 1- appropriate study design;

• sample size• matched case-control• confounding

- minimized selection bias;• asymptomatic nature• lacked HCV knowledge • available of HCV test only in some secondary or tertiary cares• self-deferral system

- minimized information bias;• masked• face-to-face interview• physical examination

- minimized misclassification of HCV status;• confirmatory tests

Publications

The risk factors for HCV infection among blood donors in northern Thailand: Matched case-control study.

Presenter: Lakkana Thaikruea (The XV International AIDS Conference. July 10-16, 2004.

Bangkok, Thailand)

Risk Factors for Hepatitis C Virus Infection Among Blood Donors in Northern Thailand

Lakkana Thaikruea1,6, Satawat Thongsawat3,6, Niwat Maneekarn4,6, Dale Netski 5, David L. Thomas ,5 Kenrad E. Nelson2 (Transfusion, 2004 - in process)

Other Related Publications

Epidemiology of hepatitis C virus infection among blood donors in northern Thailand

Presenter: Lakkana Thaikruea (International Centers for Tropical Disease Research

Network, 12th Annal Meeting, May 13-15, 2003, NIH, Bethesda, MD, USA)

Relationship between HIV and Hepatitis C Viral Genotypes and Routes of Transmission among Blood Donors in Northern Thailand.

Presenter: Lakkana Thaikruea) (11th CROI retrovirus and Opportunistic Infection

Conference, Feb 7-11, 2004, San Francisco, CA , USA)

Khop Khun Krup