9.11. Chickenpox (Varicella)

Standard Operating Procedure for the Surveillance of Chickenpox (Varicella)

Effective Date: [Date]

Version: 1.0

Prepared by: [Name/Department]

Approved by: [Name/Department]

Introduction

Purpose

The purpose of this SOP is to provide a comprehensive guide for healthcare providers, public health officials, and relevant stakeholders in surveillance of Chickenpox (Varicella). 

Scope

This SOP applies to all healthcare facilities, public health departments, and vaccination centers involved in the administration of vaccines, the monitoring of VPDs, and the management of vaccine-related activities. 

CHICKENPOX (VARICELLA)

Overview

The varicella-zoster virus (VZV) causes varicella (chickenpox) with acute primary infection and herpes zoster (shingles) by endogenous reactivation from latency. In temperate countries acquisition of infection tends to be at a younger age with greater than 90% infected by adolescence in absence of vaccination programme. In tropical regions however, an older age distribution is observed. Large outbreaks of varicella can occur every 2 – 5 years and there is a predominance of occurrence of cases in the winter/spring or cool/dry months.  

Because VZV is highly contagious secondary attack rates from varicella cases can ranging from 61–100%. The virus is transmitted from person-to-person primarily by inhalation of aerosols from vesicular fluid of skin lesions, by direct contact with rash and possibly by infected respiratory tract secretions. The incubation period, from time of contact to rash onset, is generally 14–16 days, with a range of 10–21 days. 

Clinical presentation

The prodrome consists of fever, malaise and anorexia and can precede the rash by several days. The rash consists of new crops of skin lesions which progress over five to seven days from macules to papules, to pruritic vesicles and then scabs, with unvaccinated individuals often typically having approximately 300 lesions. Crops of rash on affected regions in various stages of development is a typical feature of this disease. VZV can be transmitted one to two days before rash onset and until the lesions have crusted.  

Varicella is usually mild and self-limited. Rare severe complications include pneumonia, cerebellar ataxia, encephalitis, haemorrhagic conditions and bacterial superinfection of skin lesions. Serious disease with visceral organ involvement can occur in immunocompromised persons. 

Groups at high risk for more serious disease and complications of primary VZV infection include infants < 1-year old, pregnant women, adults and immunocompromised persons. 

Herpes Zoster (shingles) occurs as a result of reactivation later in life of latent VZV. It is characterized by a vesicular rash usually in a single dermatome accompanied by radicular pain, which can last from two to four weeks. Active Herpes Zoster can transmit VZV to susceptible people, causing varicella (chickenpox). Post herpetic neuralgia is a common and often debilitating complication of herpes zoster and can cause persistent pain for months to years after the rash resolves.

SURVEILLANCE PROCEDURES

Step 1: Case Detection and Reporting – Healthcare Providers / Laboratory Personnel 

Report all suspected cases with 48 hours. Reports should be shared with laboratory personnel for confirmation as needed. (Clinical case confirmation can be shared with the Epidemiology Unit). 

Case Definitions (WHO, 2018)

Suspected Case Definition for Case Finding:

Acute onset of a generalized maculopapulovesicular rash with concomitant presence of papules, blisters, pustules or crusts appearing on trunk and face and spreading to extremities, without other apparent cause.

Final Case Classification:

Laboratory-confirmed: A suspected case with laboratory evidence of acute VZV infection by one of the following methods:

• Detection of VZV DNA (using PCR)
• Direct antigen detection of VZV from an appropriate clinical specimen (for example, direct fluorescent antibody (DFA) testing)
• Isolation using viral culture
• Seroconversion or a significant rise (fourfold or greater) in varicella-zoster IgG titre between acute and convalescent sera by any validated serologic assay.

Epidemiologically linked confirmed case: A suspected case that is epidemiologically linked to a laboratory confirmed case, another case confirmed by epidemiologic linkage, or another clinically compatible case of VZV.

Epidemiologic linkage requires contact between two people involving a plausible mode of transmission at a time when:

• One of them is likely to be infectious (one to two days before rash onset until lesions have crusted)

AND

• The other has illness 10–21 days after contact (the incubation period).

Clinically compatible case: A case that meets the suspected case definition, is not laboratory-confirmed and is not epidemiologically linked to another clinically compatible or confirmed case.

Other Definitions

Vaccine associated varicella: A varicella-like rash in a person vaccinated 5–42 days prior to rash onset, or isolation of vaccine-type virus from rash that occurs during that interval after vaccination. 

Modified varicella in a vaccinated person (also known as breakthrough varicella): is varicella due to wild-type virus that occurs in vaccinated people (> 42 days after vaccination). Modified varicella is usually mild, with < 50 lesions, low or no fever, and shorter duration of rash. The rash may be atypical in appearance with predominance of maculopapular lesions and fewer vesicles. 

Step 2. Laboratory Confirmation

Samples should be taken to the labs to be tested (collection and transport details below)

Specimen Collection

The diagnosis of varicella is usually made clinically by the characteristic clinical presentation of the rash with fever. 

If a country chooses to conduct laboratory testing, several types of specimens can be collected.

• Skin lesions are the preferred specimen, which is collected by unroofing a vesicle (preferably a fresh fluid-filled vesicle) with a sterile needle and swabbing the base of the lesion with a sterile polyester swab with enough vigour to ensure epithelial cells are collected. Do not use cotton swabs.
• If the rash comprises only macules or papules, scrape the lesion (with the edge of a glass microscope slide, for example), swab the abraded lesion with a polyester swab, and then use the same swab to collect any material that was accumulated on the object that was used to scrape the lesion (avoid contaminating the sample with blood if direct fluorescent antibody test (DFA) is to be used). Swabs can be used for PCR, DFA or viral culture. Swabs for PCR should be transported dry or in universal transport media for culture.
• Crusts or scabs from skin lesions are excellent specimens for PCR testing but not for DFA or culture. To collect these, crusts should be lifted off the skin, placed into an empty tube and transported dry. 

The swabs and crusts should be transported at ambient temperature and arrive at the laboratory as soon as possible.

• For paired IgG antibody testing a venepuncture blood specimen can be collected and sent to the laboratory for testing. Blood collection tubes can be those for serum or plasma. Serum and plasma samples may be stored for up to five days at 2–8 °C or four weeks at -20 °C. An acute specimen should be taken within the first few days of illness, and the convalescent specimen should be taken at least three weeks later. For acute varicella, cheek and throat swabs and oral fluid are nearly as reliable as skin lesion samples and scabs. 

Step 3: Treatment, and control 

Follow international / national guidelines for treatment

If there is an outbreak 

Outbreak Response

An outbreak is an increase in varicella cases over baseline, tightly clustered in place and time. Because varicella outbreaks are so widespread in the absence of a vaccine programme, investigations should be prioritized among potentially high-risk individuals in well circumscribed settings such as hospitals, jails and day care facilities with infants.

Public health response measures:

• Once an outbreak is confirmed, enhanced surveillance with line listing should be conducted to keep track of cases and document outcomes, particularly complications. If not already established, surveillance should continue through two full incubation periods (42 days) after the rash onset of the last identified case to ensure that the outbreak has ended.
• Vaccination is recommended to control the outbreak and prevent spread. Single-dose varicella vaccine administered within three to five days of exposure has proved to be highly effective for prevention of disease (> 70%), the earlier after exposure the higher the efficacy
• If vaccination is contraindicated or refused the person should be excluded from school or work for up to 21 days after the last case is identified to prevent infection. 
• VZV immune globulin can be effective for post-exposure prophylaxis if given soon after exposure, to reduce disease severity in persons at high risk for severe varicella such as pregnant women, immunocompromised persons and neonates. 
• Post-exposure prophylaxis with antiviral medications has been shown to prevent clinical disease in immunocompromised children. 

Step 4: Reporting 

Reports of all clinically / laboratory confirmed cases should be shared with the Epidemiology Unit 

Step 5: 

Data Management (Epi Unit) 

• Data should be cleaned and analysed 
• Preparation of a report should be done on the evolution of the epidemiological situation of the disease (this can be done under VPD)
• Dissemination of a weekly situation report