timing and design of repeat surveys in asia: outcomes of ... · 8 | myanmar – sample size...

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Timing and design of repeat surveys in Asia: outcomes of

February 2012 workshop

5th meeting of the WHO Global Task Force on TB Impact Measurement

Geneva, 9-10 May

Babis Sismanidis

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Overview

Background to the February 2012 workshop

Bangladesh

Myanmar

the Philippines

Viet Nam

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Background to workshop

Four Asian countries are planning repeat TB prevalence surveys around 2015: Bangladesh, Myanmar, the Philippines and Viet Nam

Repeat surveys are more methodologically demanding than stand alone surveys (Chapter 9, the Lime Book)

Workshop to support these four Asian countries

– Learn from recent experience in Cambodia and China

– Discuss internationally recommended design and optimal timing for repeat surveys

– Group work to explore plausible sample size scenarios

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Bangladesh

National TB prevalence survey completed in 2008

52,098 survey participants (15 years of age), participation rate 80%

Prevalence under-estimated due to survey design

Another prevalence survey is planned for 2013/2014

It will be designed as a first (and not a repeat) survey

Rates per 100,000

(95% CI) 2010

Smear positive 63

(44-89)

Design effect = 2.7

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Myanmar – Background

National TB prevalence survey completed in 2010


Large variability in between-cluster prevalence (k)

Repeat survey planned for 2014 (4 years later)

Rates per 100,000

(95% CI) 2010

Bacteriologically-

confirmed

613

(502-748)

k=0.62

Smear positive 242

(186-315)

k=0.81

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Myanmar – Factors driving prevalence

2010 – 2014

DOTS expansion, low coverage of MDR

Low level HIV

PPM expansion

Faster economic expansion expected

Limited health insurance

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Case studies: Cambodia, China

ANNUAL CHANGE Cambodia China

Time period 2002-2011 2005-2010

GDP per capita +10 +20

HIV prevalence among TB -5.6 NA

% 0-14 over total population -2.6 -1.2

TB expenditure +5.7 +9

PPM NA NA

ACSM NA NA

Ratio of suspect:notification NA -5.8

Notifications

Smear positive

All forms

-4.6

4.7

-3.4

-0.7

PREVALENCE

Smear positive

Bacteriologically-confirmed

-5.6

-4.9

-9.0

-5.8

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Myanmar – Sample size calculation

Annual decrease in TB prevalence (both outcomes): 5% Smear positive outcome: p1=242 → 194

Bacteriologically-confirmed outcome: p1=613 → 490

1Perform sample size calculation as a stand-alone survey, based on precision. 2Perform sample size calculation assuming 2010 prevalence estimate is the true level of prevalence. 3Perform sample size calculation assuming 2010 prevalence level and allowing for uncertainty around this level 4Perform sample size calculation using prior information from 2010 survey to inform anticipated values of prevalence in 2014

20% precision, 20% reduction compared to 2010 prevalence levels, same cluster

size and k as with the 2010 survey

Method of calculation Smear positive outcome Bacteriologically-confirmed outcome

Single survey1 110,844 54,750

Repeat surveys2 145,270 71,540

Repeat surveys3 Undefined Undefined

Bayesian4 90,520 Not yet calculated

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Myanmar – Conclusions

Smear positive outcome: prohibitively large sample sizes required

– either due to the level of prevalence is not very high

– or due to short duration between the two surveys

Bacteriologically-confirmed outcome: single survey approach feasible

Consider delaying the survey to 2016/2017 in order to allow for large reductions in prevalence levels to be reached

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the Philippines – Background

National TB prevalence surveys conducted in 1997 and 2007


Rates per

100,000

(95% CI)

1997 2007 Annual

decrease (%)

Bacteriologically-

confirmed

960

(750-1160)

660

(510-810)

k=0.55

3.7%

Smear positive 360

(280-450)

260

(170-360)

k=0.79

3.3%

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the Philippines – Factors driving prevalence

1997 – 2007 – DOTS expansion, low coverage of MDR

– Low level HIV

– PPM expansion

– Slow economic expansion

– Limited health insurance

2007 – 2014 (sustained levels of decrease in TB expected) – Some more PPM (PPM coverage currently stable)

– Universal health insurance?

– Faster economic growth?

– MDR control (target 30% DST in retreatment)

– Negative factors: diabetes rising fast, aging population

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the Philippines – Sample size calculation

Annual decrease in TB prevalence (smear positive): 3.3% Annual decrease in TB prevalence (bacteriologically confirmed): 3.7% Smear positive outcome: p1=260 → 200


1Perform sample size calculation assuming 2007 prevalence estimate is the true level of prevalence. 2Perform sample size calculation assuming 2007 prevalence level and allowing for uncertainty around this level 3Perform sample size calculation using prior information from 2007 survey to inform anticipated values of prevalence in 2014

20% precision, 23% and 26% reduction respectively for smear positive and

bacteriologically confirmed compared to 2007, same cluster size and k as with the

2007 survey


Repeat surveys1 88,557 38,054


Bayesian3 47,517 18,855

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the Philippines – Conclusions

Decline 2007–2014 should not be assumed faster than decline 1997–2007

Smear positive outcome: – use Bayesian approach, but still almost 50,000 (too expensive)

– do the survey in 2017 or later instead of 2014

Bacteriologically-confirmed outcome: the survey may show an overall decline since 1997

Consider delaying the survey to 2017 – Too late for an MDG assessment

– But evidence from 3 surveys indicating the country is on track

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Viet Nam – Background

National TB prevalence survey conducted in 2007


Large variability in between-cluster prevalence (k)


Rates per 100,000

(95% CI) 2007

Bacteriologically-

confirmed

307

(249-366)

k=0.59

Smear positive 197

(150-244)

k=0.75

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Viet Nam – Factors driving prevalence

2007 – 2014

DOTS expansion, low coverage of MDR

Low level of HIV: Antenatal clinic surveillance 0.37% in 2005, 0.25% in 2010, an annual decrease of -9.3%

PPM expansion: currently only covers about 5% of private health providers

Fast economic expansion. Total increase between 2007 and 2010 in GDP per capita is about 10%

Aging of the population

Suspect:Notified smear positive ratio increased from 10.4 in 2007 to 11.4 in 2010

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Viet Nam – Sample size calculation

Annual decrease in TB prevalence (both outcomes): 4.3% Smear positive outcome: p1=197 → 138


1Perform sample size calculation assuming 2007 prevalence estimate is the true level of prevalence. 2Perform sample size calculation assuming 2007 prevalence level and allowing for uncertainty around this level 3Perform sample size calculation using prior information from 2007 survey to inform anticipated values of prevalence in 2014

20% precision, 30% reduction compared to 2007 prevalence levels, same cluster

size and k as with the 2007 survey


Repeat surveys1 95, 524 81,517


Bayesian3 Not yet calculated 133,592

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Viet Nam – Conclusions

There is political commitment in the country to measure the level of prevalence in 2015, in order to assess if the West Pacific Region target of 50 % reduction in prevalence, compared with 2000 levels, has been reached.

2007 survey only one culture per survey participant. The repeat survey should culture two specimens instead.

To end up with less than 100,000 the repeat survey must be: – conducted when the reduction in prevalence is more than 30% compared

with the 2007 survey, which could be around 2015/2016,

– consider using bacteriologically-confirmed as the primary outcome,

– consider using the Bayesian approach to sample size calculation.

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Next steps

Produce and disseminate workshop report

Follow up with all four countries and continue TA

Communicate with funding agencies for the possibility of ensuring funds even is surveys are delayed

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Acknowledgements

Contributing to the background document: Maridel Borja, Muhammad Farid, Katherine Floyd, Sian Floyd, Philippe Glaziou, Cornelia Hennig, Thandar Lwinn, Fulvia Mecatti, Sukyi Myo, Binh Hoa Ngueyn, Viet Nhung Nguyen, Nobu Nishikori, Ikushi Onozaki, Nemia Sucaldito, Yinyin Xia, Norio Yamada

Contributing to the repeat prevalence survey work: Cambodia, China

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Question to the Task Force

Do you agree with the provisional conclusions from the February 2012 workshop?

timing and design of repeat surveys in asia: outcomes of ... · 8 | myanmar – sample size...

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