Varicella-zoster virus infection (chickenpox) is a viral infection occurring in childhood. Almost all children in the Netherlands will get this infection at some point. People with chickenpox get red macules on the skin all over the body, including the scalp. The macules become papules within a few hours and then become the characteristic vesicles within 24 hours. First they contain bright fluid and then progress onto crusted papules. The crusts disappear after one to two weeks. Over the course of several days, new crops of vesicular rash appear and follow the same progression. The presence of different efflorescenses at the same moment is typical of this infection. The vesicles may also appear as painful ulcers in the mouth or throat and sometimes on the genitals. Chickenpox is often itchy and may also cause some pain. General illness and fever also occur. Fever, malaise and loss of appetite are common in the prodromal phase in the days before the rash appears and small, crater-like scars may remain after the healing of the skin lesions. Chickenpox is caused by the varicella-zostervirus (VZV), which is a herpesvirus. It is transmitted by aerosols in droplets of the nasopharyngeal secretions of an infected person or by direct cutaneous contact with fluid from the vesicles. It is a very contagious infection and the incubation period ranges from 10 to 21 days, but more typically lasts 14 to 16 days. Infected persons can infect others from two days before the first skin lesions appear until all vesicles have fully crusted over. This infectious period lasts approximately seven days in immunocompetent persons. Normally, a varicella-zoster virus infection occurs only once in a person.

The diagnosis is based on the typical clinical picture. In dubious cases, a PCR test of the vesicle fluid may be considered for confirmation. In general practice, testing is generally not necessary.

After healing, the virus withdraws through sensory nerve pathways to sensible ganglia, where it is suppressed by cellular immunity. The virus can become active again when cellular immunity is reduced. It then spreads through the sensible nerve pathway to the corresponding dermatome, resulting in herpes zoster (shingles). This is usually a painful rash with vesicles in the supply area of a sensory nerve and occurs in all age groups, with the incidence increasing in higher age groups.

In healthy children, varicella-zoster virus infection has a mild and self-limiting course. Many cases of chickenpox are not presented to the GP. A secondary bacterial infection of the vesicles sometimes occurs (in 5% of cases) and is often caused by S. pyogenes or S. aureus. Other complications, such as neurologic complications (acute cerebellar ataxia and encephalitis), are rare. Primary varicella infection in children increases the risk of soft tissue infection with invasive group A streptococci. This may lead to serious complications, such as necrotising fasciitis and toxic shock syndrome.

In immunosuppressed hosts, varicella-zoster virus infection may run a more serious course because of reduced cellular immunity. This may be the case for patients receiving immunosuppressive therapy after a solid organ transplantation or those who are HIV positive.

New-borns infected intra-uterine via the mother having a varicella infection late in her pregnancy are also at high risk for severe complications of varicella.

A varicella-zoster virus infection generally runs a more serious course in immunocompetent hosts aged 12 years and older than in young children. Varicella pneumonia, a rare complication occurring mainly in adults, is difficult to treat.

Education about the disease and its mild course in healthy children is important. Treatment is focused on symptom relief, such as drying or cooling lotions. Bacterial superinfections of chickenpox can be treated with local antibiotics. In extensive or persistent impetiginisation, oral antibiotics can be considered.

Oral antiviral therapy is not indicated in uncomplicated varicella-zoster virus infections in immunocompetent children. It may be considered in immunocompetent patients aged 12 years and older within 24 hours after the onset of skin lesions to reduce the disease duration. Infected patients from other risk groups and infected patients with (serious) complications should be referred and receive intravenous antiviral therapy.

In the Netherlands and other parts of the world with a moderate climate, seroprevalence of varicella-zoster virus at the age of 12 is more than 95%. In countries with a warmer climate, seroprevalence is much lower. As a result, the occurrence of chickenpox among adults can be higher there and causes more severe morbidity.

Some countries have started a vaccination programme against varicella-zoster virus infection, reporting a decreased incidence and a milder course of infection in vaccinated children and a lower complication rate. The Netherlands has not yet started a national vaccination programme.

Varicella-zoster virus infection (chickenpox) is recorded with the ICPC code A72. Herpes zoster (shingles) has the code S70. If the diagnosis of chickenpox cannot be made (for example, in a telephone consultation), a symptom diagnosis may be recorded.

The symptom diagnosis ‘rash localised’ has the code S06. ‘Rash generalised’ is coded S07 and ‘lumps / swellings generalised’ S05. ‘Other viral exanthem’ can be recorded as A76.

The overall incidence of chickenpox is 2.7 per 1000 patient years. It is a disease of childhood, with an incidence of 27.7 per 1000 patient years in the age group 0-4. This means that in a practice with 1000 patients aged 0-4, chicken pox is diagnosed almost 28 times a year in this young age group. In the age group 5-14, the incidence is 2.7 per 1000 patient years. In older age groups the diagnosis is rare. Link/Figure 1 The incidence between the different sexes is roughly equal.

Chickenpox is ranked number 18 of most common new diagnoses among children aged 0-4. Link/Table 2

The overall prevalence of chickenpox is 2.8 per 1000 patient years, with the highest prevalence in the age group 0-4 (29.2 per 1000 patient years in those aged 0-4). This means that among 1000 patients aged 0-4, 29 patients (parents) contact their GP during the year because of chickenpox. Link/Figure 3

The similar numbers of incidence and prevalence indicate that chickenpox is an acute (episodic) disorder. Occasionally, it demands repeated GP attention crossing the calendar year border.

The rolling three years average trend graphs show a decrease in chickenpox incidence and prevalence since 2019, which cannot be explained other than as an effect of the COVID-19 pandemic that started in 2020.

The most common RFE at the start of an episode of chickenpox is ‘chickenpox’ (A72), in 43% of all episodes, which means that chickenpox is easily recognised by many parents. This is followed by a request for advice (*45) as an initial RFE. Other common RFEs are various symptoms of chickenpox: localised rash (S06), generalised rash (S07) and fever (A03) (6%), followed by generalised lumps / swelling (S05) and pruritus (S02). A request to check the skin (*31), to prescribe medication (*50) or to write some sort of note or letter (*62) are other RFEs. Airlines repel infective persons with chickenpox, resulting in requests for fit-to-fly declarations. Link/Table 4

The most common intervention in episodes of chickenpox is providing education / advice / observation (*45), recorded in 75% of episodes. Link/Table 5 The prescription of medication occurs in 14% of episodes and a referral to secondary care (the paediatrician) is needed in only 1% of episodes. Link/Table 6 Medication prescription involves topical antibiotics (e.g. fusidic acid, in 4% of episodes), zinc products (in 2%), other emollients and protective agents (in 2%) and local anaesthetics (amides, e.g. lidocaine, in 1%). Link/Table 7 In the rare case of chickenpox in patients aged 15 and older, the prescription of medication occurs more frequently, in 29% of episodes. Link/Table 8

Dutch guideline: https://richtlijnen.nhg.org/ behandelrichtlijnen/waterpokken#volledigetekst (2019)

Albrecht MA. Clinical features of varicella-zoster virus infection: Chickenpox. In: UpToDate, Hirsch MS, Kaplan SL, Mitty J (Eds), UpToDate, Waltham, MA, 2023

Patient information: http://huidziekten.nl/folders/ nederlands/waterpokken.htm