**3.1 Usefulness of patch testing**

Patch testing remains the gold standard for the diagnosis of ACD (Devos & Van Der Valk, 2002; Uter W et al, 2009). Quality control of patch testing is both a prerequisite for, and an objective of, clinical epidemiology of contact dermatitis. Continuous development of test standards concerning the composition of test series, test concentration, and vehicle and standardization of test readings is provided by the national and international research groups on contact dermatitis.

Many studies in contact dermatitis are based on populations that have been patch tested; usually this means that the participants visited a clinic or a hospital for being evaluated on having contact dermatitis. There are a variety of types of irritant reactions - some can look identical to allergic reactions. The recognised convention for recording patch test reactions is as follows:


#### **3.2 Measures of disease frequency (incidence and prevalence)**

The epidemiologist deals with necessity of data on defined populations. The most basic setting giving rise to epidemiological data is the evaluation of the occurrence of a disease in the presence of an exposure. The exposure may be present or absent and the disease may be present or absent.

Measures of disease frequencies include *prevalence*, which is the amount of disease that is already present in a population; *incidence*, which refers to the number of new cases of contact dermatitis during a defined period in a specified population; and "incidence rate" (IR), which is the number of non-diseased persons who become diseased within a certain period of time, divided by the number of person-years in the population. All measures of disease frequency consist of the number of cases as the numerator, and the size of the population under study as the denominator. Sensitivity and specificity of the diagnostic instruments used are important. In epidemiological studies, an overestimation of prevalence can result from low sensitivity/specificity.

The three most important types of observational study in the epidemiology of contact dermatitis are follow up studies, case-control studies and cross-sectional studies. In follow-

Sosted et al, 2005; Lerbaek et al, 2007). Several studies have investigated the incidence of hand eczema in the general population (Bo et al, 2008; Hald et al, 2008; Moberg et al, 2009;

Hand eczema is the most frequent occupational skin disease. In many jobs the skin on the hands is subjected to damage caused by contact with skin irritants and contact allergens. Several studies have investigated the incidence and prevalence of hand eczema in the

Patch testing remains the gold standard for the diagnosis of ACD (Devos & Van Der Valk, 2002; Uter W et al, 2009). Quality control of patch testing is both a prerequisite for, and an objective of, clinical epidemiology of contact dermatitis. Continuous development of test standards concerning the composition of test series, test concentration, and vehicle and standardization of test readings is provided by the national and international research

Many studies in contact dermatitis are based on populations that have been patch tested; usually this means that the participants visited a clinic or a hospital for being evaluated on having contact dermatitis. There are a variety of types of irritant reactions - some can look identical to allergic reactions. The recognised convention for recording patch test reactions is

The epidemiologist deals with necessity of data on defined populations. The most basic setting giving rise to epidemiological data is the evaluation of the occurrence of a disease in the presence of an exposure. The exposure may be present or absent and the disease may be

Measures of disease frequencies include *prevalence*, which is the amount of disease that is already present in a population; *incidence*, which refers to the number of new cases of contact dermatitis during a defined period in a specified population; and "incidence rate" (IR), which is the number of non-diseased persons who become diseased within a certain period of time, divided by the number of person-years in the population. All measures of disease frequency consist of the number of cases as the numerator, and the size of the population under study as the denominator. Sensitivity and specificity of the diagnostic instruments used are important. In epidemiological studies, an overestimation of prevalence

The three most important types of observational study in the epidemiology of contact dermatitis are follow up studies, case-control studies and cross-sectional studies. In follow-

Lind et al, 2007).

general population.

**3.1 Usefulness of patch testing** 

groups on contact dermatitis.

+/− doubtful: faint erythema only + weak: erythema, maybe papules ++ strong: vesicles, infiltration

can result from low sensitivity/specificity.

**3.2 Measures of disease frequency (incidence and prevalence)** 

+++ extreme: bullous IR: irritant

present or absent.

as follows:

up studies, selection of subjects is based upon exposure to the factor of interest. Instead of exposure, the presence or absence of a risk factor (e.g. nickel allergy, or atopy) can also be chosen as basis for comparison. In case-control studies, the subjects are selected according to their disease status. Information on the past exposure of the persons with contact dermatitis (cases) and the non-diseased persons (controls) is collected. In cross-sectional studies, a study population is selected regardless of exposure status or disease status (in contrast to case-control and follow-up studies).

Data on the incidence and prevalence of occupational dermatoses are scarce. The most important sources of data are occupational disease registries, case series of patients visiting dermatology clinics, and a limited number of cross-sectional studies in one or more occupational groups.

#### **3.3 Incidence and prevalence of contact dermatitis and contact sensitisation**

*Incidence of hand eczema:* Several studies have investigated the incidence of hand eczema in the general population (Lantinga et al, 1984; Yngveson M, 2000; Meding & Jarvholm, 2004; Brisman J et al, 1998; Meding et al, 2006; Lind, 2007; Lerbaek et al, 2007). The median incidence rate was 5.5 cases/1000 person-years (range 3.3–8.8). Stratified by sex, the median incidence rate of hand eczema was 9.6 cases/1000 person-years (range 4.6–11.4) among women and 4.0 cases/1000 person-years (range 1.4–7.4) among men (Thyssen et al, 2010).

*Prevalence of hand eczema:* Few studies showed that the 1-year median prevalence of hand eczema in the general population was 9.7% (11.4% among women and 5.4% among men) and that the 1-year weighted average prevalence was 9.1% (10.5% among women and 6.4% among men) (Lantinga et al, 1984; Agrup, 1969; Peltonen, 1979; Menné et al, 1982; Kavli & Forde, 1984; Meding, 1990; Meding & Swanbeck, 1987; Meding & Jarvholm, 2002; Ortengren, 1999; Meding et al, 2001; Brisman J et al, 1998; Montnemery et al, 2005; Bo et al, 2008; Fowler et al, 2006; Hald et al, 2008; Svedman et al, 2007; Lind et al, 2007).

Population studies may give valuable information on the magnitude of the disease problem. Different data was found when compared the frequencies of positive path-tests reactions in the general population and in eczema patients at a dermatological clinic in the same area (Menné & Knudsen 1997) (Table 1). Publications based on data of patients visiting dermatology clinics and/or patch testing units can not be used to directly derive population related incidence or prevalence estimates. Data from incidence studies may support and direct strategies for the prevention of contact allergy and ACD, supporting conclusions derived from clinical surveillance data.

Nickel sulphate is the most common allergen in the standard series and the most common cause of allergic contact dermatitis, particularly in women. This gender difference is traditionally explained by increased exposure in women, due to direct skin contact with nickel-releasing metal, such as in jewellery, wristwatches, and clothing accessories. A possible association between nickel allergy and hand eczema in women has been addressed and supported by several population-based studies, whereas an association has been questioned in men (Nielsen et al, 2002; Peltonen, 1979; Meijer et al, 1995) (Tables 2 and 3).

Epidemiology of Contact Dermatitis 9

Barros et al, 1991 562 Standard series 0.9 Neomycin, thimerosal,

Mortz et al, 2001 1146 TRUE-tests 8.6 Nickel, fragance mix,

Table 3. Studies on contact dermatitis in children (general population) (list is not extensive).

**3.4 Current view on the spectrum of contact allergy to important sensitizers across** 

In 2005, the Spanish Society of Allergology and Clinical Immunology (Sociedad Española de Alergología e Inmunología Clínica (SEAIC) in collaboration with the Allergy and

Positive

314 Standard series 7.6 Neomycin, nickel, and

424 Epiquick test 14.9 Nickel, cobalt, and

reaction to nickel; total (%)

Three most common allergens

p-tertiary-butylphenol-

thimerosal/colophony

2.5 Chromium, HgCl2, and

formaldehyde

formaldehide

MCl/MI

and

/cobalt

chromium

patch testing

and PPD

Fig. 1. Etiologic agents for contact dermatitis in *Alergológica*-2005.

Study *n* Allergens used for

Röckl et al, 1966 357 Not given; MCl/MI

Weston et al,

Dotterud & Falk,

1986

1994

**Spain** 


Table 1. Comparison of frequencies of positive patch-test reactions in the general population and in eczema at a dermatological clinic in the same area of greater Copenhagen in 1990 (Menné & Knudsen 1997).


Table 2. Studies on contact dermatitis in the general population (list is not extensive).

Table 1. Comparison of frequencies of positive patch-test reactions in the general population and in eczema at a dermatological clinic in the same area of greater Copenhagen in 1990

> Positive reaction to nickel; total (%)

Three most common allergens

cobalt/Balsam of Peru

and thimerosal

and thimerosal

dichromate, and palladium chloride

and potassium dichromate

dichromate, and cobalt

thimerosal

chloride

25.8 Nickel, potassium

patch testing

Nielsen et al, 1992 567 TRUE-tests 6.7 Nickel, thimerosal,

Nielsen et al, 1998 469 TRUE-tests 10.8 Nickel, fragance mix,

Schäfer et al, 2001 1141 Standard series 9.9 Nickel, fragance mix,

Lazarov, 2006 2156 TRUE-tests 13.9 Nickel, fragrance mix,

Table 2. Studies on contact dermatitis in the general population (list is not extensive).

1161 Spanish standard series

542 Standard series 19.1 Nickel, potassium

1236 TRUE-tests 17.6 Nickel, cobalt, and

(Menné & Knudsen 1997).

Akasya-

Dotterud & Smith-Sivertsen,

García-Gavín et

2007

al, 2011

Hillenbrand, 2002

Study *N* Allergens used for


Table 3. Studies on contact dermatitis in children (general population) (list is not extensive).

#### **3.4 Current view on the spectrum of contact allergy to important sensitizers across Spain**

In 2005, the Spanish Society of Allergology and Clinical Immunology (Sociedad Española de Alergología e Inmunología Clínica (SEAIC) in collaboration with the Allergy and

Fig. 1. Etiologic agents for contact dermatitis in *Alergológica*-2005.

Epidemiology of Contact Dermatitis 11

Myroxylon pereirae (5.3-6.8%), cobalt chloride (6.2-8.8%) or thiuram mix (1.7-2.4%), the differences observed with other allergens may hint on underlying differences in exposures, for example: dichromate 2.4% in the UK (west) versus 4.5-5.9% in the remaining EU regions, methylchloroisothiazolinone/methylisothiazolinone 4.1% in the South versus 2.1-2.7% in

The continuous collection and analysis of data within multicenter clinical epidemiology offer practical findings. Thyssen et al (2007) described main findings from epidemiological population-based studies (Table 2) investigating contact allergy in the general population or

Work-related dermatoses, in particular hand dermatitis, are still among the most prevalent occupational diseases. Understanding the epidemiology of OCD is essential to determine etiologic factors of the disease and to make recommendations for its

Fig. 2. Incidence rates of ICD and ACD in the occupational groups with the highest risk for

Different professions have differing risks for occupational skin disease. Those at the highest risk for a contact dermatitis are hairdressers (yearly rate 120/100,000), printers (rate

occupational skin diseases (Diepgen & Coenraads PJ, 2000).

the remaining regions (Uter et al, 2009).

subgroups of the general population.

prevention.

**4. Occupational contact dermatitis** 

Immunology Laboratory Abelló undertook the "Alergológica 2005" study with the aim of obtaining epidemiologic, clinical and socioeconomic information on allergic patients seen and treated by Allergology specialists in Spain.

In the particular case of contact dermatitis, the results from epicutaneous tests from the standard Spanish series for contact dermatitis were recorded by taking readings at 48 and 96 hours, and evaluating erythema-infiltration, papules and vesicles. Two hundred-six cases of contact dermatitis were diagnosed, which represents a prevalence of 4.1%. The mean age of the patients was 42.5 years and females clearly outnumbered men (2.5:1). In the etiology of contact dermatitis (Figure 1), the leading causes were metals, nickel and cobalt, together with chromium, with a total of 91 cases. Thiomersal is in third place with 13 cases, which represents 6.2% of all causes (Muñoz-Lejarazu, 2009).

#### **3.5 Current view on the spectrum of contact allergy to important sensitizers across Europe**

In 1996 a European surveillance network was created to analyze routinely collected data in various contact allergy units in several European countries (European Surveillance System on Contact Allergies [ESSCA]; www.essca-dc.org). ESSCA has been fully operational since 2001, with several surveillance networks currently participating, among them the British Contact Dermatitis Group; the IVDK in Germany, Switzerland, and Austria; the Northeast Italian Contact Dermatitis Group; and, more recently, the 5 hospital dermatology departments affiliated with the Spanish Group for Research Into Contact Dermatitis and Skin Allergy/Spanish Surveillance System on Contact Allergies (Hospital del Mar, Barcelona; Hospital La Princesa, Madrid; University General Hospital, Alicante; Complexo Hospitalario Universitario, Santiago de Compostela; and University Hospital Puerto Real) (García-Gavín et al, 2011). Nickel sulphate remains the most common allergen with standardized prevalences ranging from 19.7% (central Europe) to 24.4% (southern Europe). While a number of allergens shows limited variation across the four regions, such as


Table 4. Main findings from epidemiological population-based studies (published between 1966 and 2007) investigating contact allergy in the general population or subgroups of the general population (Thyssen et al, 2007).

Immunology Laboratory Abelló undertook the "Alergológica 2005" study with the aim of obtaining epidemiologic, clinical and socioeconomic information on allergic patients seen

In the particular case of contact dermatitis, the results from epicutaneous tests from the standard Spanish series for contact dermatitis were recorded by taking readings at 48 and 96 hours, and evaluating erythema-infiltration, papules and vesicles. Two hundred-six cases of contact dermatitis were diagnosed, which represents a prevalence of 4.1%. The mean age of the patients was 42.5 years and females clearly outnumbered men (2.5:1). In the etiology of contact dermatitis (Figure 1), the leading causes were metals, nickel and cobalt, together with chromium, with a total of 91 cases. Thiomersal is in third place with 13 cases, which

**3.5 Current view on the spectrum of contact allergy to important sensitizers across** 

1. Contact allergy was independent of enhanced IgE responsiveness. 2. The median prevalence of contact allergy was 20% (adults 15–69 years).

6. The median prevalence of nickel allergy among women was 17.1%.

9. Nickel contact allergy may be associated with hand eczema in women.

observed in both children and adults.

general population (Thyssen et al, 2007).

increasing significantly over the past 4 decades.

7. A median prevalence of 81.5% women, have pierced ears. 8. Pierced ears are a strong risk factor for nickel allergy.

10. Heavy smoking may be a risk factor for nickel allergy.

thimerosal.

In 1996 a European surveillance network was created to analyze routinely collected data in various contact allergy units in several European countries (European Surveillance System on Contact Allergies [ESSCA]; www.essca-dc.org). ESSCA has been fully operational since 2001, with several surveillance networks currently participating, among them the British Contact Dermatitis Group; the IVDK in Germany, Switzerland, and Austria; the Northeast Italian Contact Dermatitis Group; and, more recently, the 5 hospital dermatology departments affiliated with the Spanish Group for Research Into Contact Dermatitis and Skin Allergy/Spanish Surveillance System on Contact Allergies (Hospital del Mar, Barcelona; Hospital La Princesa, Madrid; University General Hospital, Alicante; Complexo Hospitalario Universitario, Santiago de Compostela; and University Hospital Puerto Real) (García-Gavín et al, 2011). Nickel sulphate remains the most common allergen with standardized prevalences ranging from 19.7% (central Europe) to 24.4% (southern Europe). While a number of allergens shows limited variation across the four regions, such as

3. Contact allergy to a wide range of allergens as well as multiple contact allergy was

4. Contact allergy was most commonly observed against nickel, fragrances, and

5. The proportion of nickel allergy out of contact allergy to at least 1 allergen has been

Table 4. Main findings from epidemiological population-based studies (published between 1966 and 2007) investigating contact allergy in the general population or subgroups of the

and treated by Allergology specialists in Spain.

represents 6.2% of all causes (Muñoz-Lejarazu, 2009).

**Europe** 

Myroxylon pereirae (5.3-6.8%), cobalt chloride (6.2-8.8%) or thiuram mix (1.7-2.4%), the differences observed with other allergens may hint on underlying differences in exposures, for example: dichromate 2.4% in the UK (west) versus 4.5-5.9% in the remaining EU regions, methylchloroisothiazolinone/methylisothiazolinone 4.1% in the South versus 2.1-2.7% in the remaining regions (Uter et al, 2009).

The continuous collection and analysis of data within multicenter clinical epidemiology offer practical findings. Thyssen et al (2007) described main findings from epidemiological population-based studies (Table 2) investigating contact allergy in the general population or subgroups of the general population.
