Hepatitis A: Epidemiology

Hepatitis A is one of the most common human infectious diseases. In terms of the number of cases reported, hepatitis A ranks third after acute respiratory viral diseases and gastrointestinal infections. Hepatitis A occurs on all continents and in all countries, while the incidence rate depends on the sanitary and hygienic conditions and the cultural level of the population. According to WHO, the highest incidence is recorded in developing countries in Asia, Africa and Latin America. In Western Europe, the incidence of hepatitis A is less than 20-30 per 100 thousand of the population, while in the countries of South-Eastern Europe and the Middle East they range from 200 to 500, while in the countries of Asia and Africa they rise to 1000 or more per 100 thousand of the population.

On the territory of Russia, the incidence varies widely. In recent years, it has been characterized by a rapid decline, which can be explained by the pronounced periodicity inherent in this infection and the structural changes taking place in the Russian population (falling fertility, eliminating nurseries, pioneer camps, etc.).

About the wide spread of hepatitis A The results of the virological and serological examination of various contingents (mainly donors) in some cities of Russia, as well as in Europe, America and Asia, are evidence of this.

Hepatitis A is mainly affected by children. In this sense, this infection is rightly called a childhood illness. The specific gravity of the incidence of children under 14 in the total incidence of hepatitis A, according to international statistics, is 60% or higher. To date, most of the reported epidemics and outbreaks occur in children. In all countries, including in our country, the most striking age is from 3 to 7 years. This is particularly clearly seen in the CIS regions with a high incidence. For example, in Uzbekistan, the incidence of pre-school children is many times higher than the incidence in other age groups. The same pattern is observed in Turkmenistan, Tyva, Tajikistan and other regions with high rates of hepatitis A. In places with a relatively low incidence, the greatest number of patients is registered in older groups of children - 12-14 years. However, the shift in the age-related morbidity to the side of the 7th most senior population can not be considered a rule, rather it is a temporary exclusion, followed by an increase in the incidence among children aged 3-7 who are the most vulnerable group for hepatitis A.

Children of the first year of life with hepatitis A practically do not get sick or get sick very seldom. Among the 120 children of the first year of life who were on inpatient treatment for viral hepatitis, 40% of cases documented hepatitis B, 30 - hepatitis C, 10 - cytomegalovirus hepatitis, only 7 - hepatitis A, in 13% of cases Hepatitis remained undeciphered. The low incidence of hepatitis A in children of the first year of life is due to the presence of transplacental immunity received by the child from the mother, the nature of their nutrition, and also the limited contacts of such children. Theoretically, of course, we can assume that children of the first year of life can get hepatitis A, especially if they have not received specific antibodies from the mother or they have already lost these antibodies. This situation can be observed in cases when the mother is seronegative for anti-HAV and / or the pregnancy ended with the birth of a deeply premature baby. However, this coincidence, although possible, is apparently rare, since practically the entire adult population of our country is seropositive against anti-HAV.

Transplacental antibodies in children of the first year of life undergo total catabolism by 8-12 months, and from this age children become susceptible to the hepatitis A virus. They begin to acquire active immunity, which, naturally, is possible only if they are infected with the hepatitis A virus. This process on different territories is not the same, it is determined by the level of morbidity, sanitary condition of the population, crowding and other factors. For example, American authors note that in Pennsylvania (USA), children have virtually no antibodies to the hepatitis A virus, while in Costa Rica, half of the children surveyed already have these antibodies in 2 years, in Texas (USA), anti-HAV have been detected 13% of children under 5 years old, in China - 42, in Nigeria - 60, in Australia - 4%.

With increasing age, the number of people seropositive for antibodies to the hepatitis A virus is rapidly increasing.

The frequency of detection of anti-HAV in different age groups of healthy populations in some countries and territories (%)

A country	Age, years
	10-19	10-29	30-39	40-49	50 and more
Sweden	1	3	9	25	36
Norway	4	5	Eleven	65	58
Speyshriya	6th	12	Thirty	54	61
Netherlands	7th	36	64	77	74
France	25	53	71	87	82
West Germany	14	Зі	66	84	94
Greece	68	83	89	88	89
Belgium		64	88	89	91
Former Yugoslavia	95	99	95	98	93
Israel	93	83	95	98	98
Senegal	100	91	67	67	59
Taiwan	95	89	90	83	83
USA	10	23	40	44	63
China	78	87	87	81	78
Nigeria	-	95	99	97	-

As can be seen from the presented data, in most countries the highest percentage of people seropositive for anti-HAV is observed at the age of 50 years or more. The only exceptions are Taiwan, Senegal, Israel, the countries of the former Yugoslavia and, in part, China, where the number of people with anti-HAV reaches a maximum at the age of 10-19, which may indicate epidemic troubles for hepatitis A in these countries. However, such a conclusion can not be considered absolutely reliable, since these data are mostly selective and they need not necessarily reflect the incidence of hepatitis A in the country as a whole.

On the other hand, the decrease in the number of people with anti-NAU with increasing age, as in Senegal, for example, can be explained by a decrease in the antibody titer in older age groups. A low percentage of seropositive people aged 10-19 in highly developed countries, such as Sweden, Norway, Switzerland, the Netherlands, Germany, France and the USA, deserves attention, which undoubtedly reflects the high social and hygienic standard of living in these countries.

The noted regularities in the immune stratum with respect to hepatitis A in general are typical for our country. Studies in 1999 showed that in Moscow children aged 5-6 years in the serum, antibodies to the hepatitis A virus were detected in 50% of cases, 11-12 years in 90%.

In Central Asia and in other regions with a high incidence of hepatitis A, immunity is acquired at an earlier age, and by the age of 10-15 almost all have become immune.

[1], [2], [3], [4], [5], [6], [7], [8],