Francesco Checchi Disease Control in Humanitarian ... · IDHE Short course | London, 30 March-3 April 2009 Disease Control in Humanitarian Emergencies (DCE) 27 Indicators for interventions

IDHE Short course | London, 30 March-3 April 2009

Disease Control in Humanitarian Emergencies (DCE)1

Francesco Checchi

Disease Control in Humanitarian Emergencies (DCE)

Department of Epidemic & Pandemic Alert and Response (EPR)

Review of epidemiological indicators

Short course on Infectious Diseases in Humanitarian Emergencies

London, 30 March 2009



Why compute epidemiological indicators?

� Describe morbidity

� Incidence

� Prevalence

� Losses in life expectancy and quality of life

� Describe mortality

� Mortality rate

� Excess mortality

� Describe coverage or effectiveness of relief interventions

� Different stages of interventions





Types of indicators

� Proportion

� A/N, where A is part of N

� Can be expressed as %

� Ratio

� A/B, where A is not part of B

� Rate

� Speed with which events are accumulating

� New cases per person per unit time

� Lots of misnomers -> very confusing!



Some ground rules for formulating indicators

� Define condition clearly

� “Malaria” could be “P. falciparum infection”, “P. vivax infection”, or “disease due to malarial infection”

� Time-Person-Place

� “Diarrhoea affects one out of four kids…”. Try: “The point prevalence of diarrhoea (defined as more than 3 stools per day) among children aged under 59 months living in camp A is 26.3%”

� Avoid absolute figures

� Numerator and denominator

� “120 nets were distributed…” (yeah, but how many people were targeted?)

� “130 cases occurred in August…” (in the entire country? in a district? out of how many people?)

� Try to not call them all a “rate”







� Incidence

� Prevalence



� Mortality rate








� Incidence

� Prevalence



� Mortality rate






� Computed among population at risk

� Neonatal tetanus?

� Prostate cancer?













Prevalence

� Population = 400

� Point prevalence on 1st January 2002 ?

1st January 2001 1st January 2002



Prevalence

� 4 cases among 400 persons

� Point prevalence = 4 / 400 = 0.01 = 1 %

� Period prevalence in 2001?

1st January 2001 1st January 2002



Which would you describe with incidence or prevalence?

� Bloody diarrhoea due to type 1 shigella

� Falciparum malaria

� TB

� HIV/AIDS

� Herpes simplex



Proportional morbidity (all ages), February 2004

26,7%

14,8%

8,9%

18,4%

4,6%

5,1%

9,5%

9,2%

2,8%

malaria

schistosomiasis

watery diarrhoea

bloody diarrhoea

ARI

STD

worms

circulatory problems

others

Proportionate morbidity

consultations/admissions due to all causes

consultations/admissions due to disease



Other burden of disease indicators

� Disability Adjusted Life Years (DALYs) lost

� Years of Life Lost (YLL)

� Healthy Life Years (HeaLYs) lost

� QUALYs

� Mainly useful to compare diseases and rationalise aid and research allocation

� Based on consensual but arbitrary decisions on disability weights





� Incidence

� Prevalence



� Mortality rate






� Unit: per n persons per unit time

� Emergencies: deaths per 10 000 per day (per 10 000 person-days)

� Alternatives: deaths/1000/month, deaths/1000/year

What is a mortality rate?

deaths during period

(population present during

period x time in the period)

Crude Mortality Rate =

deaths <5 yrs during period

(population <5 yrs present x

time in the period)

Under 5 Mortality Rate =







Emergency thresholds

� “Non-crisis” CMR in Sub-Saharan Africa: 0.3 to 0.6 per 10 000 per day (Sphere: 0.44), approximately double for U5MR

� Fixed thresholds: CMR 1 per 10 000 per day, U5MR 2 per 10 000 per day

� Context-specific thresholds (Sphere, 2004): doubling from pre-crisis values

� SSA: CMR 0.9, U5MR 2.3

� Latin America: CMR 0.3, U5MR 0.4

� Everyone agrees CMR should rapidly fall below 1!



CMR versus excess death tolls

Iraqi Kurds (CDC, 1991):

� CMR peak 10.4

� 3 months, population 400,000

� 6,200 excess deaths

DRC (IRC, 2004):

� CMR 0.7

� 16 months, population 64 million

� 500,000 excess deaths (3.8m since 1998)





� Incidence

� Prevalence



� Mortality rate






Indicators for interventions

� Coverage

� Proportion (%) of people in need of intervention who actually

receive it

� Vaccination coverage

� Proportion of malnourished children receiving nutritional

rehabilitation

� Sometimes as a ratio: e.g. people per latrine ratio

� Effectiveness

� Proportion (%) of people who experience intended positive

outcome of intervention, out of those who actually receive it



Effectiveness indicators

� Specify intended benefit!

� Many possible effectiveness measures for same intervention; e.g.

IRS could achieve

� Reduction in P. falciparum prevalence in general population (outcome)

� Reduction in incidence rate of clinical malaria among children <15y old

(outcome)

� Reduction in under-five mortality rate attributable to malaria (impact)

� Reduction in child mortality due to any cause (ultimate impact)

� Efficacy versus effectiveness

� Ideal versus field conditions

� For curative interventions: cure “rate”





Indicators to monitor interventionsIndicators to monitor interventions

� Coverage is never known, must be measured

� Effectiveness can often be assumed, so coverage = proxy for impact for some interventions (ex. vaccination, bednets, vitamin A)

� Effectiveness of health services can never be assumed

inputsinputs

processesprocesses

outputsoutputs

outcomesoutcomes

impactimpact

coverage x coverage x

effectivenesseffectiveness

coveragecoverage

DEATHSDEATHS

services providedservices provided

resources brought inresources brought in



Diagnostic accuracy

� Sensitivity

� Proportion of true cases that are detected

� Specificity

� Proportion of true non-cases that are correctly classified as non-

cases



� Relative risk

� risk in

exposed /

risk in

unexposed

� RR>1

� Risk factor

� RR<1

� Protective

factor



Conclusions

� Clear time-person-place reference

� Clear definitions

� Disease/condition

� Intervention or risk factor

� Intended benefit of intervention

� Numerator and denominator whenever possible

� Avoid vague or incorrect terminology

� We have to understand each other!

Documents

Francesco Checchi Disease Control in Humanitarian ... · IDHE Short course | London, 30 March-3 April 2009 Disease Control in Humanitarian Emergencies (DCE) 27 Indicators for interventions