Arne Høst, ledende overlæge, dr. med.

H. C. Andersen Børnehospital

Odense Universitetshospital

Hvad kan kohortestudier bruges til?

En prospektiv uselekteret fødselskohorte

født i Odense Kommune

01.11.98 – 30.11.99 (”DARC-Kohorten”)

Causality or coincidence ?

Associations are not causations!

Decreasing number of

storks & newborns

Prospective longitudinal birth

cohort studies

Natural history of disease and phenotypes

Risk factors, predictors, determinants

Incidence

Prevalence

Prospective evaluation of exposure (quantity,

duration)

Effect of genetic and environmental interaction

Temporality of events

The criteria for proving causality

between an environmental exposure

and a non-infectious illness

Biological plausible

Analogous associations

Temporality

Dose-response effect

Consistency

Decrease in effect when exposure ceases

Hill AB. The environment and disease: association

or causation? Proc R Soc Med 1965;58:295-3000

Evaluation of different kind of studies

Study Utility

Retrospective Not useful

Cross-sectional Not useful

Prospective non-interventional Generate hypotheses

Prospective interventional Proper confirmation

Assessment of cause-effect relationships between exposure

to allergens/adjuvant factors and the development of allergic

disease

Studies on development of allergic

diseases - important factors

• Prospective vs retrospective

• Randomisation + blind ascertainment

• Unselected vs. selected HR sample

• Age of the population

• Duration of intervention

• Pre-definition of outcome measures

• Well defined diagnostic criteria

• Investigation at onset of symptoms/disease

• Control for confounding

• Compliance and drop-out

• Duration of follow-up

• Sample size – power/adequate statistical analyses

Best evidence for

recommendations

Randomisation not possible:

• Breastfeeding

• Environmental tobacco smoke

Best evidence for recommendations

The randomised controlled trial is traditionally

the gold standard for judging the benefits of

treatment/intervention mainly because it is

conceptually easier to attribute any observed effect

to the treatment/intervention being compared

High quality observational studies may extend

evidence over a wider population and are likely to

be dominant in the identification of risk factors/

predictive factors and when randomised controlled

studies be unethical or impractical

Development of allergic disease

Genetic factors

Environmental exposure to allergens

Food allergens

Inhalant allergens

Other risk/protective factors e.g.

Tobacco smoke

Infections

Microbial flora

Other (antioxidants?)

The development and phenotypic expression of

allergic disease depends on an interaction between:

Age, dose and duration of exposure important

Synergistic effects

Increased prevalence of allergic diseases

Environmental factors ?

Western life-style ?• Increased exposure to allergens / adjuvants

• Changed exposure to infections / microbial

flora ? (Hygiene hypothesis)

• Changes in diets and obesity ?

Er forekomsten af allergi stigende?

Definition

Resultater fra danske undersøgelser

• Fødselskohorter fra 1985 og 1998-1999

• Nordborg Kommune 1990-1991 og 2001

Allergi - definition

Allergi er en overfølsomhedsreaktion udløst

af immunologiske mekanismer

(immunologisk mekanisme påvist eller stærkt

mistænkt)

A revised nomenclature for allergy

An EAACI position statement. Allergy 2001;56:813-824

WAO. JACI 2004;113:832-6

Atopi - definition

Atopi er en personlig eller familiær tendens

til at producere IgE antistoffer som respons

på lave doser af allergener, oftest

proteiner, og til at udvikle typiske

symptomer som astma, rhinoconjunctivitis,

eller eksem / dermatitis

A revised nomenclature for allergy

An EAACI position statement. Allergy 2001;56:813-824

WAO. JACI 2004;113:832-6

Overfølsomhed

Allergisk overfølsomhed(immunologisk mekanisme påvist

eller stærkt mistænkt)

Nonallergisk overfølsomhed

(immunologisk mekanisme

udelukket)

IgE-medieret Ikke IgE-medieret

Nonatopisk Atopisk T celle: f.eks. kontakt

dermatitis, celiaci

Eosinophile: f.eks.

gastroenteropati

IgG-medierede: f.eks.

allergisk alveolitis

Andre

Insekt stik

Orme

Lægemidler

Andre

A revised nomenclature for allergy. EAACI position statement. Allergy 2001;56:813-824; WAO. JACI

2004;113:832-6

Changes in asthma prevalence:

two surveys 15 years apart

Cross-sectional study 12 year old

1973 1988

n 818 n 965

Wheeze, ever 17% 22%

Asthma, ever 6% 12%

Asthma current 4% 9%

Eczema 5% 15%

Hay fever 9% 15%

BHR, PEF var. ≥ 15% 6.7% 7.7%

Burr ML et al. Arch Dis Child 1989;64:1452-56

Odense fødselskohorter

Odense

fødselskohorte

1985

Alle

1 år

1749

15 år

Prospektiv

Non-

intervention

Komælksallergi

(alle)

Allergisk sygdom

(n276)

DARC-

fødselskohorte

1998-1999

562

uselekterede

nyfødte

562

6 år

Prospektiv

Non-

intervention

Allergisk sygdom

Odense fødselskohortestudie 1985

* Udvalgt tilfældigt blandt hele studiepopulationen

Fødsels kohorte, Odense 1985: 1758 nyfødte

9 døde neonatalt

Uselekterede = stikprøve*: 276 børn (16%)

Follow-up ved 1½ year: 276 børn

Follow-up ved 5 years: 256 børn (93%)

Follow-up ved 10 years: 226 børn (82%)

Follow-up ved 15 years: 219 børn (79%)

Results

Odense birth cohort 1985

Prevalence (%(n)) of atopic symptoms

in unselected children18 mo

N 256*

5 years

N 256

10 years

N 223

15 years

N 216

Atopic dermatitis14% (36) 6% (14) 10% (23) 7% (16)

Food allergy7% (19) 4% (10) 8% (17) 4% (9)

Asthma2% (4) 5% (12) 8% (18) 9% (19)

Rhinoconjunctivitis0.4% (1) 2% (5) 6% (14) 12% (27)

* Only children who participated at 5 yrs are included.

Høst A et al. PAI 2002

1749 infants

210 (12%) no CM formula 1539 (88%) + CM formula (40-860

ml)

0 CMPA 39 CMPA (40-830 ml CM formula)

40 ml CM formula equals 0.4 g BLG

0.4 g BLG equals BLG of 8000 L Human milk

Høst A et al. Acta Paediatr 1988;77:663-70

Food Allergy and CMPA in two comparable

unselected birth cohorts in Odense, 14 years apart,

in young children 0-18 months

Cumulated incidence (95% CI)

1985

(n 1,749)

1999

(n 495)

FA 7.4% (6.2-8.6) 3.2% (1.8-5.0)

CMPA 2.2% (1.5-2.9) 1.0% (0.1-1.7)

Danish Allergy Research Centre

The DARC birth cohort

Observational / non-intervention study

562 unselected children

• Recruited from maternity ward OUH

Followed prospectively birth 6 years

(1998 2004)

• Inclusion data at birth + 6 ”follow-ups”

DARC KohortenPh.D.-afhandlinger

Lene Annette Norberg: Environmental factors and atopic

pre-disposition as predictors for the development of asthma,

rhinoconjunctivitis and other atopic diseases in mucous

membranes in childhood.

Hanne Jøhnke: A comparison between criteria for diagnosing AD

Morten Østerballe: The prevalence of food hypersensitivity in an

unselected population of children and adults

Henrik Kjær: The prevalence of allergic diseases in an unselected

group of 6 year old children. The DARC birth cohort study

Esben Eller: Food allergy and atopic dermatitis in childhood.

Longitudinal results from the DARC cohort.

Cumulated incidence of atopic diseases in two birth cohorts 14 years apart

Cumulated incidence

up to18 months

1999 1985

Recurrent wheeze 25.1% 21.4%

Asthma 5.1% 1.6%

Hay fever 0.4% 0.4%

Food allergy/intolerance 3.4% 7.4%

Cow’s milk allergy 0.9% 2.2%

Patterns of sensitization in infants and its relation to atopic dermatitis.

Jøhnke H, Norberg LA, Vach W, Høst A, Andersen KEPediatr Allergy Immunol. 2006 Dec;17(8):591-600

Sensitization ever to ≥ 1 allergen at 18 months of age

was 59%, 50% and 6% using HR, IgE and SPT,

respectively. A transient sensitization to ≥ 1 allergen

was found in 47%, 42% and 4% and a persistent

sensitization in 17%, 10% and 3%, respectively.

Sensitization to environmental allergens was

frequently observed in infancy when testing with HR

and IgE. Results of SPT gave much lower

frequencies. Reactivity to foods was more frequent

than to aeroallergens.

The dominant pattern was low-level transient

sensitization

Sensitization to cow’s milk and egg, CAP RAST

cl 1 (≥ 0.35) & cl 2 (≥ 0.7) up to 18 months of life

Norberg LA. Ph.D.Thesis 2003

Jønhke H. Ph.D. Thesis

N 470 Danish unselected children. DARC cohort

0

2

4

6

8

10

12

14

3mo 6 mo 12 mo 18 mo

Age

%

Cows milk cl 2

Cow's milk cl 1

Hens egg cl 2

Hens egg cl 1

Prevalence of food hypersensitivity - DARC

Questionnaire, SPT, HR, spec. IgE, oral challenge

FHS

486 children 3 years of age: 2.3%

1.6% egg

0.6% milk

0.2% peanut

301 children > 3 years of age 1.0%

936 adults 3.2%

0.4% peanut

Estimated FHS to pollen related foods in pollen sensitized adults 32%

Østerballe M et al. PAI 2005

DARC at 6 years, n 404

Current prevalence

AD 14.4% (11.3-18.1)

Asthma 6.2% (4.2-9.0)

ARC 5.7% (3.8-8.4)

Any allergic disease 25.7%

Food allergy 1.2% (0.4-3.0)

Kjær H, PAI 2008

Food sensitization and subsequent allergic disease

0

10

20

30

40

50

60

70

80

Asthma Atopic dermatitis Rhinoconjunctivitis Any

%

Never sensitized (n=243)

Early sensitized only (n=36)

Late sensitized only (n=26)

Persistently sensitized (n=20)

* p<0.05, ** p<0.01, *** p<0.001

NS

NS

NS

NS

NS

NS

***

******

***

*

**

Inhalant sensitization and subsequent allergic disease

* p<0.05, ** p<0.01, *** p<0.001

0

10

20

30

40

50

60

70

80

Asthma Atopic dermatitis Rhinoconjunctivitis Any

%

Never sensitized (n=225)

Early sensitized only (n=48)

Late sensitized only (n=35)

Persistently sensitized (n=17)

NS

NS

NS

NS

***

*

*** *** **

***

***

*

DARC Cohort

Development of asthma 0-6 years

In food allergics 4/15 (26.6%)*

In non-food allergics 21/389 (5.4%)*

*p< 0.01

Odds Ratio 6.4 (1.4-23.8)

Kjaer HF et al. PAI 2009

Point-Prevalence of FHS

0

1

2

3

4

3 6 12 18 36 72

Age (mo)

%

Peanut

Egg + Peanut

Egg

Milk + Egg

Milk

No children allergic to wheat, soy or fish!

(n) 2 6 16 13 5

Frequency of Atopic Dermatitis

0

5

10

15

20

25

3 6 12 18 36 72

Age (months)

%Line: cum. incidence

Bar: point-prevalence

Point-prevalence of AD and FHS

0

2

4

6

8

10

12

3 6 12 18 36 72

Age (months)

%

From birth to 6 yrs. of age:

23% have AD

4% have food

hypersensitivity

90% of children with

FHS have AD

15% of children with AD

develops FHS

Sensitization to food is a normal phenomenon in

children without food allergy

Irrelevant sensitization to foods in food-allergic

children

Children with AD, but without FHS, are neither

more frequently nor having higher levels of IgE

than children without AD

Sensitization

Strong association between allergic

sensitisation and childhood allergic diseases

Preventive Measures. Section 1: Early Interventions. Høst A, Boner A, Odhiambo J, Custovic A,

Lockey R. In Johansson SGO, Haahtela T (eds): Prevention of Allergy and Allergic Asthma. World

Allergy Organisation Project Report and Guidelines. Chem Immunol Allergy. Basel, Karger 2004,

vol. 84; 135-151

Allergen exposure sensitisation

Sensitisation allergic disease

Allergen exposure allergic disease

Foods - food allergy +

Inhalants - asthma?

- allergic asthma + (?)

Breastfed high risk infants differed from formula fed high risk infants regarding the following characteristics:

age at introduction of solid foods 5 vs 4 monthsexposure to tobacco smoke at home 28% vs 46%exposure to tobacco smoking by mother13% vs 29%exposure to pets 33% vs 42%socioeconomic class

Exposure to environmental factors in a birth cohort of atopic predisposed infants fed human milk or a

hydrolysed cow’s milk based formula

Halken et al. Pediatr Allergy Immunol 2000;11:149-161.

A prospective, randomized intervention study. N 478

Decreased exposure to ETS?

Comparable data from two Danish birth cohorts 13 years apart:

Year Numbers Exposure to ETS at home/daycare

1985 n 276* 66%

1998-1999 n 562 69%

During the same period the ”official” frequency of female smokers

decreased from 42% to 30%!

* Random sample of a one year birth cohort of 1746 newborns.

The reason for discrepancy?

”Official” TS data Method of TS registration

1985 birth cohort Questionnaire, selfreported

Structured interview

1998-1999 birth cohort Questionnaire, structured

interview + CO in exhaled air

of parents

Questionnaire data on TS may be invalidated by recall bias and/or

information

Norberg LA. Predictors of development of allergic diseases in mucous membranes. Ph.d. thesis.

University of Southern Denmark, Odense University, 2003: Odense, Denmark.

Christensen Estmann A. J Pediatr Epidem 2004.Smoking and Allergy. A prospective cohort study

of infants at hign risk for allergy development. Ph.d. thesis. University of Southern Denmark.

Odense University, 2004: Odense, Denmark.

Cross-sectional investigations

Nordborg 1990 and 2001

Results 1990-1991

(n=851)

2001

(n=939)

Asthma 4.0% 3.6% Ns

BHR 3.2% 2.0% Ns

Asthma and BHR 7.2% 5.6% Ns

Zilmer M et al. 2009 DPS

Prospective longitudinal birth

cohort studies

• Natural history of disease and phenotypes

• Risk factors, predictors, determinants

• Incidence

• Prevalence

• Prospective evaluation of exposure (quantity,

duration)

• Effect of genetic and environmental interaction

• Temporality of events

Many thanks to my colleagues:

- Lene Annette Norberg

- Hanne Jøhnke

- Morten Østerballe

- Henrik Fomsgaard Kjær

- Esben Eller

- Susanne Halken

- Carsten Bindslev-Jensen

Eller E et al. Development of atopic dermatitis in the DARC birth cohort.

PAI 2009.

Kjaer HF et al. The association between early sensitization patterns and

subsequent allergic disease. The DARC birth cohort study. PAI 2009.

Eller E et al. Food allergy and food sensitization in early childhood: results

from the DARC cohort. Allergy 2009.

Eller E et al. Meta-analysis of determinants for pet ownership in 12

European birth cohorts on asthma and allergies: a GA2LEN initiative.

Allergy 2008.

Kjaer HF. Spirometry in an unselected group of 6-year-old children: the

DARC birth cohort study. Pediatr Pulm 2008

Kjaer HF et al. The prevalence of allergic disease in an unselected group

of 6-year-old children. The DARC birth cohort study. PAI 2008.

Jøhnke H et al. Patterns of sensitization in infants and its relation to

atopic dermatitis. PAI 2006.

Keil T et al. European birth cohort studies on asthma and atopic

diseases: II. Comparison of outcomes and exposures – a GA2LEN

initiative. Allergy 2006.

Keil T et al. European birth cohort studies on asthma and atopic dieases:

I. Comparison of study designs – a GALEN initiative. Allergy 2006.

Osterballe M et al. The prevalence of food hypersensitivity in an

unselected population of children and adults. PAI 2005.

Jøhnke H et al. A comparison between criteria for diagnosing atopic

eczema in infants. Br J Dermatol 2005.

Jøhnke H et al. Reacitivity to patch tests with nickel sulfate and fragrance

mix in infants. Contact Dermatitis 2004.

Increase in allergic diseases

over 3-4 decades?

Asthma (A) +

Allergic/atopic

Non-atopic

Allergic rhinitis (AR) +

Atopic dermatitis (AD) ++

Food allergy (FA) -

Methodology to confirm an

increase

Same method/design 10-20 years apart,

same region

Questionnaires?

Questionnaires + interview?

Q+I + objective parameters (clin. exam.,

IgE, SPT, LF)

Grades of Recommendations - WHO

A. Requires at least one randomized controlled trial as part of a body of literature of overall good quality and consistency addressing the specific recommendation. (Evidence levels Ia, Ib)

B. Requires the availability of well-conducted controlled clinical studies without randomization. (Evidence levels IIa, IIb)

C. Requires evidence obtained from well designed descriptive studies, comparative studies, correlation studies and case studies. (Evidence level III)

D. Requires evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities. Indicates an absence of directly applicable clinical studies of good quality. (Level IV)

Breastfeeding

• Exclusively breastfeeding 4 months is associated with a

lower cumulative incidence of FA/CMPA and eczema until

3 years and recurrent wheeze/asthma until 6 years

Prospective, observational non-interventional

studies have shown:

Muraro A, Dreborg S, Halken S, Høst A, Niggemann B, Aalberse R et al. Dietary prevention of

allergic diseases in infants and small children. Part III: Critical review of published peer-reviewed

observational and interventional studies and final recommendations. Pediatr Allergy Immunol.

2004 Aug;15(4):291-307.

Observational studies

• Disease related modification of exposure

– Mothers of children with allergic symptoms

before weaning tend to breastfeed longer

• May not be able to control for selection

bias and reverse causation as regards the

effect of BF on AD

Kull I. JACI 2004

Lauberau B. J. Pediatr 2004

Breastfeeding reduces the risk of asthma

during the first 4 yrs

Breastfeeding ≥ 4 moAsthma at 4 years

OR [95%CI]

All 0.72 [0.53-0.97]

Children with onset of wheeze

during lactation excluded0.64 [0.46-0.88]

Only breastfeeding before the onset

of wheeze0.52 [0.39-0.69]

Mothers of children with allergic symptoms before weaning

tend to breastfeed longer

Disease related modification of exposure

Kull I.JACI 2004:114:755-60. Prospective, n 4098

Foods

Exposure Sensitisation, Food Allergy

Exposure Food Allergy Eczema

Documentation: Pro-obs-non interv. studies and

RCT in HR infants.

Muraro A, Dreborg S, Halken S, Host A, Niggemann B, Aalberse

R et al. Dietary prevention of allergic diseases in infants and

small children. Part III: Critical review of published peer-

reviewed observational and interventional studies and final

recommendations. Pediatr Allergy Immunol. 2004

Aug;15(4):291-307.

Formulas containing hydrolysed protein

for prevention of allergy and

food intolerance in infants.

Cochrane review.

The Cochrane Library 2007, issue 2

• Conclusions

– HF not better than BF!

– In high risk infants limited evidence of effect of HF compared to CMF.

• No effect on A, R, AD

• Limited evidence that pHF reduces CMPA and eHF is better than pHF

• Limited evidence that eHF prevent allergy, AD

Osborn DA, Sinn J

Specific proliferative peripheral blood monuclear cell response

Development of allergic disease

Specific IgE

Neonatal/postnatal allergen exposure

Increased risk for development of clinical allergic disease

Particularly in high risk infants

In utero allergen stimulation

What came first ?

?

Disease related modification of exposure !!!

Barton S. Which clinical studies provide the best evidence? The best RCT still trumps the best observational

study. BMJ 2000;321(7256):255-6.

Eccles M, Freemantle N, Mason J. North of England based guidelines development project: Methods of

developing guidelines for efficient drug use in primary care. Education and debate. BMJ 1998;316:1232-35.

Nickel R, Niggemann B, Grüber C, Kulig M, Wahn U, Lau S. How should a birth cohort study be organised?

Experience from the German MAS cohort study. Paed Resp Rev 2002;3:169-76.

Høst A, Halken S. Can we apply clinical studies to real life? Evidence-based recommendations from studie on

development of allergic diseases and allergy prevention. Allergy 2002;57:389-97.

Johansson SGO, Bieber T, Dahl R, Friedmann PS, Lanier B, Lockey R et al. A revised nomenclature for

allergy for global use. Report of the Nomenclature Review Committee of World Allergy Organisation, October

2003. J Allergy Clin Immunol 2004;113(5):832-6.

Johansson SGO, Haahtela T (eds): Prevention of Allergy and Allergic Asthma. World Allergy Organisation

Project Report and Guidelines. Chem Immunol Allergy. Basel, Karger 2004, vol. 84.

Muraro A, Dreborg S, Halken S, Høst A, Niggemann B, Aalberse R et al. Dietary prevention of allergic

diseases in infants and small children. Part II. Evaluation of methods in allergy prevention studies and

sensitization markers. Definitions and diagnostic criteria of allergic diseases. Pediatr Allergy Immunol. 2004

Jun;15(3):196-205.

Is early S-IgE positivity associated

to subsequent disease ?

Kulig M et al. Clin Exp Allergy 1998;28:1397-1403

Tariq SM et al Pediatr Allergy Immununol 2000;11:162-67

Retrospective view on sensitization status in children

with allergic disease at 6 years