Cockroaches are now recognised as being important indoor allergens, along with house-dust mites and domestic pets. Cockroach allergy is common in South Africa, particularly at the coast. In the Durban area, cockroach allergy is present in 80% of asthmatic children. Exposure to cockroaches is a risk factor for hospital admission with asthma in patients living in poor socio-economic circumstances. In South Africa cockroaches affect homes across the social spectrum. A recent study demonstrates that 40% of patients in Natal and Western Cape who are allergic to one or more inhalant allergens are sensitised to cockroach. The corresponding figure for the inland highveld is 32- 35 %.

What are the allergens?

The cockroach allergens are associated with proteins found in the body of cockroach; in its saliva, its remains and its dried faecal matter. The highest levels of allergens are found in kitchens. In South Africa, both the German cockroach (Blatella germanica, Bla-g-1) and the American cockroach (Periplaneta americanus) are found.

What are the clinical effects of exposure to cockroach?

Cockroach antigens are believed to play a role in the ongoing airway inflammation in certain asthmatics. Asthma attacks results in high rates of emergency room visits, hospitalisation, periods of breathing difficulty, missed school days and sleep deprived nights. The role of cockroach allergy in perennial rhinitis is yet unclear.

How is cockroach sensitivity diagnosed?

A diagnosis of allergy to cockroaches may be confirmed using a small blood sample sent to a laboratory.

It is recommended that patients allergic to cockroaches are also tested with a panel of other indoor allergens (e.g. house dust mites, dogs, cats and moulds). This is because many patients with cockroach allergy are also allergic to other indoor allergens. In particular, a recent study in South Africa has shown that there is a very high chance of simultaneous sensitisation of house dust mite (86%), Bermuda grass (64%), Timothy grass (79%), various weeds (79%), various moulds (93%) and dog dander (71%). In the USA, a recent study shows that 37% of inner-city children were allergic to cockroaches, 35% to house dust mites and 33% to cats. The study showed that 50% of the rooms had high levels of cockroach allergen, compared to 9.7% with dust mite antigen and 12.6% with cat allergen.

What is to be done?

Patients who have positive allergy tests to cockroach allergens should actively take steps to avoid exposure to cockroaches in their homes and workplace.

Cockroaches are very hardy and resistant creatures. Crevices and possible portals of entry for cockroaches into the home should be sealed off. Fumigation should be arranged when numbers of cockroaches are identified in a home. Regular cleaning of cupboards and surfaces is essential. The covering of food and the sealing of garbage is also particularly important, as well as washing plates and dishes promptly.