Eggs have become an 38% more expensive in just five years as outbreaks of bird flu drive up the price, an investigation by consumer organisation Consumentenbond has shown.

Vrije uitloop eieren or eggs from hens with access to the outdoors went up in price by 48%, while scharreleieren – eggs from chickens kept in large indoor pens – went up by 40%. Organic eggs were 26% more expensive.

According to a checks at the 13 biggest Dutch supermarkets, the scharrel eggs cost an average 35 cents a piece, followed by 37 cents for a free-range egg and 43 cents for an organic egg.

The Consumentenbond also found battery eggs, from hens that have to share a cage with 30 to 60 chicken and never see daylight, at five local shops. Supermarkets no longer sell battery eggs, except in processed foods.

The main reason for the price rises is the undiminished demand for eggs and dips in production because of frequent outbreaks of bird flu. Between October and December last year over a million chickens were culled to prevent the disease from spreading.