No 11 - 2012

Gender differences in notifiable diseases 2001-2011

Gender is a frequently overlooked parameter in the study of the epidemiology of infectious diseases. We here describe gender differences in selected notifiable infectious diseases categorized by their route of infection.

Table 1 shows gender difference as a ratio of the cumulated number of new cases per 100,000 men/women, totally and per age group for the years 2001-2011.

Blood and sexually transmitted diseases

Syphilis

The number of syphilis cases has risen in recent years, EPI-NEWS 35a/11. On 1 January 2010, syphilis screening was made part of the general screening of pregnant women, EPI-NEWS 27-33/10. Despite this, the number of syphilis cases observed among men was markedly higher than that seen in women for all age groups, and new cases were primarily seen in men who have sex with men (83% in 2010).

Gonorrhoea

The number of gonorrhoea cases followed an increasing trend until 2010, EPI-NEWS 34a/11. Markedly more cases were observed in men than women. In 2010, a total of 43% of the infected were men who had sex with men. The number of heterosexually infected men also increased during the period.

Chlamydia

The number of demonstrated chlamydia cases has remainnned stagnant in recent years, EPI-NEWS 36/11. In contrast to syphilis and gonorrhoea, the number of chlamydia cases was considerably higher among adult women than men. Women undergo routine testing more frequently than men, e.g. in connection with birth control counselling.

Hepatitis B, acute and chronic

For acute hepatitis B, an excess incidence was observed among men aged 25-64 years. This contrasts with the number of notified cases of chronic hepatitis B in the same age group. As from 2005, testing for chronic hepatitis B has formed part of the general screening of pregnant women, EPI-NEWS 41/05. The gender difference seen in the number of notified cases of chronic hepatitis B may therefore be a reflection of such intensified screening. Acute hepatitis B is frequently diagnosed in men who have sex with men (19% in 2010).

Airborne diseases

Measles

An excess incidence was seen among boys < 1 year and men aged 25-64 years. The initial MMR vaccination is offered at the age of 15 months, so for infants it can be excluded that this may be attributed to differences in vaccination coverage. It should be stressed that the observations are based on small numbers.

Meningococcal disease, types B & C

Gender differences vary from one age group to the next, but meningococcal disease caused by N. meningitidis of type B as well as C were associated with a considerable excess incidence in boys < 1 year. Again, it should be noted that observations are based on few cases.

Tuberculosis

The occurrence of tuberculosis has increased slightly in recent years, EPI-NEWS 50/11. The gender distribution reveals an excess incidence among boys < 1 year and adult men > 24 years.

Water and foodborne diseases

Pathogenic intestinal bacteria

Campylobacter and salmonella infections occurred frequently and were primarily acquired through intake of contaminated food. Overall, both infections were slightly more frequent in men.
Verocytotoxinproducing E. coli (VTEC) infection occurred more frequently among 25-64-year-old women than among men of the same age group.

Shigella infection is primarily acquired during travels abroad and via imported foods. An excess incidence was seen in 5-64-year-old women, primarily attributable to a large outbreak caused by baby corn, EPI-NEWS 35/07.

Acute hepatitis A

Acute hepatitis A infection is primarily acquired during travels to endemic areas and outbreaks in Denmark. The increased incidence among males aged 25-64 years is primarily due to a Danish outbreak among men who have sex with men, EPI-NEWS 52/04.

Commentary

Gender differences in disease patterns may be explained by risk factor differences, the behaviour of the diseased, e.g. use of healthcare services, and by biological differences. For the presented diseases, risk factor differences may explain the gender difference observed for syphilis, gonorrhoea and acute hepatitis A and B. Differences in food preferences (meat vs. vegetables) and hygiene may probably explain the gender difference observed for the foodborne diseases. Furthermore, testing frequency contributes to explaining the gender differences observed for e.g. chlamydia.

Whether biology also plays a role in the explanation of this gender difference is an interesting, but not fully explored question. For the airborne conditions described, it is likely that biological differences are in play.

(B. Søborg, S. Ethelberg, K. Mølbak, Dept. of Inf. Disease Epidemiology)