Detection of varicella zoster virus in genital specimens using a multiplex polymerase chain reaction

OBJECTIVE: To compare the relative proportions of varicella zoster virus (VZV) and herpes simplex viruses in specimens obtained from the genital lesions of adults presenting with presumed genital herpes infection. METHODS: Swabs of genital lesions from 6210 patients attending general practices, infectious diseases clinics within hospitals, or sexual health centres for treatment of their genital lesions were tested using polymerase chain reaction (PCR) technology. The multiplexed PCR was capable of detecting herpes simplex virus types 1 and 2 (HSV-1, HSV-2), VZV, and cytomegalovirus in a single sample. RESULTS: A total of 2225 patients had viruses detected by PCR. HSV-1 was detected in 36%, HSV-2 in 61%, and VZV in 2.9% of PCR positive samples. Of the 65 patients with VZV genital infection, many were thought to have HSV infection before laboratory testing. CONCLUSIONS: The finding of VZV in nearly 3% of virus positive genital specimens demonstrates that this virus needs to be considered as a differential diagnosis for genital herpetic lesions. Advice provided to patients with VZV genital infection regarding the source of infection, likelihood of recurrence, and potential for transmission of the virus will be different from that given to patients with HSV infection.     

Confirmation of herpes simplex virus type 2 infections in herpes-like genital lesions by a simple complement-fixation test.

The presence of complement-fixing antibody to an early herpes simplex virus type 2 (HSV-2) antigen (the AG-4 antigen) was correlated with HSV-2 infection in the sera of patients with genital herpes. Eighty-eight per cent of sera taken two weeks after clinical diagnosis of a primary or recurrent herpes infection in patients, confirmed to have HSV-2 by virus isolation and typing, contained the anti-AG-4 complement-fixing antibody. None of the patients with genital HSV-1 had the antibody, and only 9% of controls or patients with facial HSV-1 infection had positive results for the antibody. This correlation was used to identify genital HSV-2 infections when either no virus sample had been taken or when virus isolations had been unsuccessful. Thus, a simple complement-fixation test can confirm an HSV-2 virus infection without isolation of the virus from the herpetic lesion.     

Confirmation of herpes simplex virus type 2 infections in herpes-like genital lesions by a simple complement-fixation test

The presence of complement-fixing antibody to an early herpes simplex virus type 2 (HSV-2) antigen (the AG-4 antigen) was correlated with HSV-2 infection in the sera of patients with genital herpes. Eighty-eight per cent of sera taken two weeks after clinical diagnosis of a primary or recurrent herpes infection in patients, confirmed to have HSV-2 by virus isolation and typing, contained the anti-AG-4 complement-fixing antibody. None of the patients with genital HSV-1 had the antibody, and only 9% of controls or patients with facial HSV-1 infection had positive results for the antibody. This correlation was used to identify genital HSV-2 infections when either no virus sample had been taken or when virus isolations had been unsuccessful. Thus, a simple complement-fixation test can confirm an HSV-2 virus infection without isolation of the virus from the herpetic lesion.     

Premarket evaluation of the POCkit HSV-2 type-specific serologic test in culture-documented cases of genital herpes simplex virus type 2 [see comment

BACKGROUND AND OBJECTIVES: The genital herpes epidemic continues, in part, because patients with subclinical or atypical presentations cannot be identified by most herpes simplex virus (HSV) antibody tests. A new product, POCkit HSV-2, has been developed to rapidly and accurately detect antibodies to HSV type 2 (HSV-2) in capillary blood or serum. GOAL: Sera from patients with culture-documented genital or oral herpes were tested to determine the sensitivity and specificity of the POCkit HSV-2 rapid point-of-care antibody test (Diagnology, Belfast, Northern Ireland). STUDY DESIGN: Sera from 50 patients with culture-documented HSV type 1 (9 oral, 41 genital) and from 253 patients with genital HSV-2 were tested by POCkit HSV-2 for HSV-2 antibodies. Each subject had a positive culture for HSV within 6 months of serum collection. Sera were preselected to include only those that were seropositive to the respective virus subtype by University of Washington Western blot. RESULTS: Compared with viral culture and Western blot analysis, sensitivity of the POCkit HSV-2 test for HSV-2 antibody was 96%; specificity was 98%. CONCLUSION: This test provides rapid, accurate identification of HSV-2 antibody in subjects with established HSV infections.     

Seroprevalence of herpes simplex virus type 1 and type 2 in Turkey

BACKGROUND: Herpes simplex virus (HSV) infections are among the most common infectious diseases in humans. The prevalence of herpes simplex viruses type 1 (HSV-1) and type 2 (HSV-2) varies widely across the world. HSV-2 infection is the primary cause of genital herpes. It is highly prevalent in human populations in many parts of the world, and is the most common cause of genital ulcer disease worldwide. In spite of the large prevalence and growing incidence of herpes simplex infection (HSV-1 and HSV-2), relatively few data have been published regarding the seroprevalence of herpes simplex infection, while no data exist regarding the Turkish population. METHODS: We aimed to investigate the prevalence of HSV-1 and HSV-2 in selected populations in Turkey. A cross-sectional study was conducted involving 2082 serum samples of 725 adults, 300 pregnant women, 200 blood donors, 483 sex workers and 110 patients with genital warts and 264 hotel staff in Istanbul, Turkey. All serum samples were assessed for HSV1 and HSV-2 IgG antibodies using an HSV-type specific, enzyme-linked immunosorbent assay (ELISA). RESULTS: The prevalence of HSV-2 and HSV-1 antibodies was 4.8 and 85.3% in sexually active adults; 5.5 and 96% in blood donors; 5 and 98% in pregnant women, 17.3 and 93.6% in patients with genital warts; 8.3 and 97.3% in hotel staff; and 60% and 99% in sex workers. CONCLUSION: These results confirm a higher prevalence of HSV infection than estimated, especially in high risk groups in Turkey. The high prevalence of HSV infection underlines the need for education among these populations.     

First episodes of genital herpes in a Swedish STD population: a study of epidemiology and transmission by the use of herpes simplex virus (HSV) typing and specific serology

OBJECTIVES: To determine the proportion of herpes simplex virus type 1 (HSV-1) and HSV type 2 (HSV-2) in first episodes of genital herpes. To evaluate the use of HSV specific serology for classifying first episodes of genital herpes and for defining HSV serostatus in the patients' sexual partners. METHODS: 108 consecutive patients with first episodes of genital herpes seen at three STD clinics in Sweden from 1995 to 1999 were included in the study. HSV culture and typing were performed and serum was tested for antibodies against a type common HSV antigen and a type specific HSV-2 antigen, glycoprotein G2 (gG2). A structured interview including questions about sexual behaviour and sexual partners was taken. "Steady" partners were offered a blood test for HSV serology and counselling. RESULTS: Of 108 patients, 11 had a negative HSV culture. Of the 97 who were HSV culture positive, 44% (43/97) were typed as HSV-1 and 56% (54/97) as HSV-2. For 86 of these 97 patients, HSV serology from the initial visit was available. Of 52 primary infections, thus initially seronegative, 64% were HSV-1 infections and of 19 female primary infections 16 (84%) were HSV-1. In 17% the first episode of genital herpes corresponded to the first clinical recurrence of an infection acquired earlier in life. There was a significant correlation between having orogenital sex and being infected with HSV-1 and also a history of labial herpes in the partner. Only 20% of partners of patients with an HSV-2 infection had a history of genital herpes. CONCLUSIONS: Almost half of first episodes of genital herpes are caused by HSV-1. In young women with a primary genital infection, HSV-1 is much more frequent than HSV-2. Besides HSV typing, we found specific HSV serology of value for classifying first episodes and for diagnosing a subclinical HSV-2 infection in partners. Anamnestic data supported the suggestion that the orogenital route of transmission was common in genital HSV-1 infections.     

Incidence of herpes genitalis in Northern Ireland in 1973-83 and herpes simplex types 1 and 2 isolated in 1982-4.

During 1973 - 83 there was a pronounced rise in the number of new cases of herpes genitalis in Northern Ireland. This study of 127 patients with herpes genitalis shows that 30% had herpes simplex virus type 1 (HSV 1) and 70% had herpes simplex virus type 2 (HSV 2) infections. Of 41 sexual contacts who attended, only seven had herpes genitalis (caused in each case by HSV 2); another patient had a history of genital lesions, and one other of oral lesions, but HSV was not isolated from either patient. None of the other sexual contacts had a history of oral or genital infection. Of 31 women with herpes genitalis who consented to undergoing cervical cytology, five had atypical changes (all had primary herpes genitalis). Of these, four were infected with HSV 1 and one with HSV 2.     

Is HSV serology useful for the management of first episode genital herpes?

BACKGROUND: First episode genital herpes simplex virus (HSV) infections can be classified into three groups, primary genital herpes (no previous exposure to HSV), non-primary first episode (IgG antibody to HSV of the non-presenting type), and first episode with pre-existing IgG HSV antibodies. The use of IgM to classify first episode genital herpes has not been evaluated. OBJECTIVE: To evaluate the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of HSV-1 and HSV-2 IgM antibodies for the diagnosis of first episode genital herpes, when compared with clinical diagnosis. METHODS: Patients with a first clinical episode of genital herpes were recruited. Sera were tested for IgG antibodies to HSV-2 using an indirect enzyme linked immunosorbent assay (ELISA). Equivocal results were resolved by western blot. HSV-1 IgG and IgM and HSV-2 IgM antibodies were detected using western blot. RESULTS: 157 patients were recruited. 31 were excluded (missing data or no detectable antibodies and negative viral isolation). Therefore, 126 patients were included in the analysis. 23 (18.3%) had primary genital herpes, 34 (27.0%) non-primary first episode, and 69 (54.8%) had pre-existing genital herpes. The specificity and PPV of HSV IgM was 100%; the sensitivity was 79% and the NPV 85%. CONCLUSION: IgM HSV serology may be useful in the management of some patients with first episode genital herpes and provide an indication of the source of infection. Drawbacks include the low sensitivity and NPV, lack of availability, IgM antibodies may occasionally be produced in response to recurrent infection and, finally, IgM antibodies may take up to 10 days to develop and last 7-10 days.     

Recurrent genital herpes in a population attending a clinic for sexually transmitted diseases.

Patients with recurrent genital herpes attending a sexually transmitted disease clinic were studied and transmission of the infection was elucidated by evaluating serostatus in their partners. Of 84 patients attending for recurrent genital herpes, 94% had a herpes simplex virus type 2 (HSV-2) infection and only 6% (5 patients) a type 1 infection. The mean age of the patients was 36 years and the duration of their infection was up to 37 years (median 4 years). In most patients the number of recurrences had not decreased between the first year and the last year. About half had experienced a more severe first episode infection. Of the patients, 64% were not aware of asymptomatic shedding and the risk of sexual transmission without clinical symptoms. Of 67 steady partners of patients with genital HSV-2, 15% had a history of genital herpes. By HSV serology, HSV-2 antibodies (indicating subclinical genital herpes) were demonstrated in more than half of the partners. The duration of the relationship or condom use did not seem to influence the frequency of transmission to the partner, which may indicate an individual susceptibility for acquiring a genital HSV-2 infection. Eleven per cent of the patients were on suppressive antiviral therapy, while 39% had no experience of antiviral therapy. Type-specific HSV serology was found to be of value in counselling partners of patients with genital herpes.     

Persistence of herpes simplex virus types 1 and 2 in infected individuals.

During a 23-month period, 18 patients with facial or genital herpetic lesions were examined; culture specimens from each patient were obtained three times per week for virologic studies. The isolated viruses were identified, and the average duration of herpesvirus in lesions was determined. Herpes simplex virus type 1 (HSV-1) was isolated from facial lesions for a mean duration of 3 1/2 days. In contrast, herpes simplex virus type 2 (HSV-2) was isolated from genital lesions for a mean duration of 5 1/2 days. The duration of viral persistence in lesions of patients with mild primary infection did not seem to differ from that in patients with recurrent infection.     

Epidemiology of genital herpes simplex virus infections in a community-based sample in France: results of the HERPIMAX study

OBJECTIVE: The objective of this study was to provide information on the prevalence of herpes simplex infections in the general population in Europe. GOALS: The goals of this study were to determine the prevalence of clinically probable genital herpes and the relationship between serotype and clinical expression in a French community-based sample. STUDY: A total of 4410 subjects chosen at random were serotyped for herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2). Data on symptoms were obtained by questionnaire allowing retrospective diagnosis of clinically probable genital herpes. RESULTS: Questionnaire data and serotype were available for 3192 subjects. Seroprevalences of HSV-1 and HSV-2 were 65.6% and 15.5%, respectively. Prevalence of clinically probable genital herpes was 11.8%, identified in 11.1% of HSV-1-positive subjects and 26.8% of HSV-2-positive subjects, with a lower prevalence in those coinfected with both virus types. CONCLUSIONS: Clinically probable genital herpes was observed in one fourth of subjects with HSV-2 infections and in some subjects with HSV-1 infection. Coinfection with HSV-1 appeared to protect against symptom expression in subjects infected with HSV-2.     

National survey of diagnostic services for genital herpes

OBJECTIVE: To investigate the provision of diagnostic services for genital herpes simplex virus (HSV) infection in the United Kingdom. METHODS: National survey of laboratories providing diagnostic services for genital herpes. RESULTS: Completed questionnaires were returned from 25/32 (78%) laboratories participating in the Clinical Virology Network, including seven in London, 12 in the rest of England, one in Wales, four in Scotland, and one in Northern Ireland. Virus culture was the diagnostic method of choice in 20/25 (80%) laboratories; 5/25 (20%) routinely used HSV DNA detection by polymerase chain reaction (PCR). HSV PCR for DNA detection in cerebrospinal fluid (CSF) was available in 17/25 (68%) laboratories. Typing of isolates (HSV-1 or HSV-2) was performed routinely in 22/25 (88%) laboratories. Only 2/25 (8%) laboratories offered HSV type specific serology, although an additional 12/25 (48%) referred requests elsewhere. Consistent with this finding, the number of HSV type specific antibody tests referred to the Health Protection Agency increased by nearly fivefold between 1997 and 2003. CONCLUSIONS: Virus culture remains the preferred diagnostic method for genital herpes, despite evidence indicating that its sensitivity is suboptimal compared to PCR. As HSV PCR is widely available for testing of CSF, it is recommended that clinicians and virologists discuss ways to implement PCR testing of genital swabs, thus enabling greater diagnostic accuracy. A call is made for studies to assess the use of HSV type specific serology in genitourinary medicine (GUM) settings, now that rapid and validated assays have become available and guidelines have been issues to provide recommendations on their use.     

Increasing proportion of herpes simplex virus type 1 as a cause of genital herpes infection in college students

A retrospective review of genital herpes simplex virus (HSV) isolates collected in a university student health service over a 9-year period showed that an increasing proportion of isolates were HSV-1 rather than HSV-2. HSV-1 accounted for 78% of all genital isolates in this population by 2001, compared with 31% of isolates in 1993. BACKGROUND: Herpes simplex virus (HSV) type 1 is usually thought to cause less than 30% of genital herpes infections in the United States, but the proportion of infections resulting from HSV-1 is increasing in some populations. GOAL: The goal was to review the relative proportion of HSV-1 and HSV-2 as the cause of newly diagnosed genital herpes infections in a population of U.S. college students and to assess trends in the change of this proportion over time. STUDY DESIGN: Genital HSV isolates collected at a university student health service from 1993 to 2001 (n = 499) were reviewed retrospectively. Analyses included comparisons of isolates by HSV type, age group, and sex. RESULTS: The proportion of newly diagnosed genital herpes infections resulting from HSV-1 increased from 31% in 1993 to 78% in 2001 (P <0.001, linear trend P <0.001). HSV-1 was more common in females than males, but increases were noted for both sexes. HSV-1 was more common in persons aged 16 to 21 than in persons aged 22 or older. CONCLUSIONS: HSV-1 has become the most common cause of newly diagnosed genital herpes infections in this population of college students and reflects a reversal of the usual HSV-1/HSV-2 ratio.     

Duplex real-time polymerase chain reaction assay for detection and quantification of herpes simplex virus type 1 and herpes simplex virus type 2 in genital and cutaneous lesions

BACKGROUND: A sensitive and specific method for detecting herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) is important for diagnosing genital and cutaneous infections. GOAL: The goal of this study was to compare quantitative real-time polymerase chain reaction (qPCR) with virus culture for diagnosis of genital and cutaneous HSV-1 and HSV-2. STUDY DESIGN: A duplex qPCR system for quantification of DNA from HSV-1 and HSV-2 was developed. Duplicate swabs for PCR and virus culture were collected from 89 patients attending our sexually transmitted infection and dermatology clinic. RESULTS: The duplex qPCR had a linear measure interval of 10-10 copies/mL. The detection limit was between 1 and 5 copies per reaction. qPCR detected HSV in 57 (64%) specimens and virus was isolated in 45 (50%) cases. First-episode infections showed higher viral quantities with a median value of 4.2 x 10 copies per reaction compared with recurrent infections with 1.0 x 10 (P = 0.0002). HSV-1 was more likely to be the cause of first-episode genital infections (72%), and HSV-2 of recurrent and atypical genital manifestations (73%). CONCLUSION: Real-time PCR is a sensitive method for diagnosing genital herpes, and the duplex format is convenient for typing. The method increased the detection rate by 27% compared with virus culture.     

Update on antiviral therapy for herpes simplex virus infection

ABSTRACT: The prevalence of infection with herpes simplex virus (HSV) continues to increase largely due to the inability of current antiviral agents to eradicate latent infection. This article reviews strategies to slow the transmission of HSV infection, most importantly through the development of vaccines, as well as established and emerging choices for treatment of primary and recurrent genital herpes, herpes labialis, infections in immunocompromised hosts, and acyclovir-resistant infections. The role of chronic suppressive therapy in the management of genital herpes as well as its potential impact on transmission rates will also be discussed.
Herpes simplex virus (HSV) is a widespread pathogen in the United States, with more than 100 million U.S. citizens having serologic evidence of HSV-1 infection and 40–60 million, nearly one-fifth of the adolescent and adult population, infected with HSV-2 (1,2) . The prevalence of HSV-2, the major cause of genital herpes, has increased 30% since the late 1970s (2) . The fact that most of those infected with HSV are asymptomatic and yet may still be subclinically shedding virus further complicates efforts to slow the spread of transmission (3) . Therefore proper management of herpetic infections requires that the clinician be able to effectively diagnose those with HSV infection, to educate them regarding means of spread and symptoms indicative of infection, and to adequately treat infections which are identified in order to alleviate patient symptoms and slow the transmission of the virus. We review options for preventing infection, treating primary infections, and treating recurrent infections in order to accomplish these goals.     

Epidemiology of genital herpes - recent advances

Genital herpes is a common, distressing infection which, due to increasing incidence world-wide, has become a prominent public health issue over recent years, even throughout the decade of human immunodeficiency virus (HIV). Since the late 1970's, the prevalence of herpes simplex virus type 2 (HSV-2) infection has increased by approximately 30 percent in the US. The number of sufferers world-wide is currently estimated at approximately 86 million people. New serological methods based on the detection of type-specific antibodies to herpes simplex virus (HSV) glycoproteins have clarified issues concerning the true incidence of genital herpes, the modifying effect of prior HSV-1 infections, the changing proportions of HSV-1 genital herpes, and the importance of asymptomatic shedding. Patients' ignorance of their diagnosis along with the occurrence of atypical symptomatology and asymptomatic viral shedding of HSV all contribute to the transmission of genital herpes. Genital ulcer disease, of which genital herpes is the most common cause in developed countries, is an important risk factor in the acquisition and transmission of human immunodeficiency virus (HIV) infection and has contributed to the spread of this disorder. Risk factors for genital herpes HSV-2 are strongly related to lifetime number of sexual partners, number of years of sexual activity, male homosexuality, black race, female gender and a history of previous sexually transmitted diseases (STD). Understanding the epidemiology of genital herpes is of great importance in limiting the spread of this STD. In this review, we summarise current knowledge related to the epidemiology of genital herpes.     

Acceptance and outcome of herpes simplex virus type 2 antibody testing in patients attending an STD clinic--recognized and unrecognized infections

The majority of herpes simplex virus type 2 (HSV-2) genital infections are asymptomatic. We wanted to evaluate the acceptance of HSV-2 antibody testing among people attending an STD clinic and to estimate, after counselling, the percentage of recognized and unrecognized HSV-2 infections. First visitors to an STD clinic were invited to participate by answering a questionnaire and taking a blood test for HSV-2 antibodies. HSV-2 seropositive individuals, who were unaware of having genital herpes, were offered an HSV-2 counselling visit and follow-up. Of 1769 patients offered testing, 57% accepted. Of 152 (15%) HSV-2 seropositive individuals, 41% had a self-reported history of genital herpes, approximately 30% had genital symptoms and 30% had no genital symptoms. The percentage of patients reporting genital symptoms was much higher in HSV-2 seropositives (45%) without a history of genital herpes than in an HSV-2 seronegative group (28%). HSV-2 antibody testing should be performed generously in all cases of uncharacteristic genital symptoms.     

Frequency of acquisition of first-episode genital infection with herpes simplex virus from symptomatic and asymptomatic source contacts

Sixty-six source contacts of index patients with first-episode genital infection caused by herpes simplex virus (HSV) were evaluated for evidence of current or past HSV infections. Forty-three source contacts (65%) reported a history consistent with previous recurrent HSV infection or were experiencing a first episode of genital herpes when initially examined. However, 60% of these 43 contacts were not aware that they had transmissible HSV infection. Twenty-nine (67%) of the 43 individuals had had recent sexual contact with an index patient when lesions were present. All of the remaining 23 source contacts, who were without a history of symptoms consistent with HSV infection, had detectable neutralizing antibody to HSV; HSV type 2 was isolated from the cervix of two of these asymptomatic source contacts. Efforts to identify individuals with undiagnosed genital herpes and to instruct these individuals concerning the risk of disease transmission in the presence of lesions are needed if the rate of transmission is to be decreased; however, methods designed to decrease the rate of transmission by asymptomatic individuals must also be evaluated.     

Risk of recurrence after treatment of first-episode genital herpes with intravenous acyclovir

To determine whether intravenous acyclovir treatment for a first episode of genital herpes could prevent or reduce subsequent recurrences, we combined and analyzed the results of two independently conducted, randomized, double-blind, placebo-controlled studies. Sixty-one patients were enrolled in the two trials; 30 received the drug, and 31 received placebo. At entry the demographic, epidemiologic, and clinical features of acyclovir- and placebo-treated patients from the two centers showed no significant differences. The median time to the first recurrence and the frequency of recurrences showed no significant differences when acyclovir and placebo recipients infected with either herpes simplex virus type 1 (HSV-1) or herpes simplex virus type 2 (HSV-2) were compared. However, irrespective of treatment, the median time to the first recurrence was significantly longer (293 days vs. 69 days; P less than .02) and the frequency of recurrence significantly less (0.11 recurrences per month vs. 0.43 recurrences per month; P less than .01) among patients with HSV-1 infection as compared with those who had HSV-2. It is concluded that in patients with first-attack genital herpes, the type of HSV is the most important determinant of subsequent recurrences and that intravenous acyclovir has little effect on subsequent recurrences.     

Famciclovir reduces viral mucosal shedding in HSV-seropositive persons

OBJECTIVE: Many cases of herpes simplex virus (HSV) infection occur through asymptomatic shedding from persons without evidence of clinical disease. This study explores whether famciclovir reduces HSV shedding in HSV-2 seropositive persons with or without a history of symptomatic genital herpes. STUDY DESIGN: One hundred twenty-seven HSV-2 seropositive participants were randomly assigned to 42 days of famciclovir, followed by 14 days of washout and 42 days of placebo, or vice versa. All subjects swabbed the genital/perianal area; those with HSV-1 infection also swabbed the oral area daily for HSV DNA PCR. RESULTS: Famciclovir reduced genital and oral HSV shedding from 11.4% of days during the placebo period to 4.7% of days during famciclovir therapy. The reduction was greater in participants with a history of genital herpes (74%) than in those without such a history (30%). In multivariate analyses, famciclovir protected against total (clinical and subclinical) genital shedding among persons with a clinical history of genital herpes (RR, 0.23; 95% CI, 0.15-0.35; P < 0.001). Among HSV-2 seropositive participants without a history of genital herpes, 60% had HSV detected in the genital area at least once during the study. Famciclovir therapy did not result in a statistically significant reduction in total HSV shedding in participants without a history of genital herpes. CONCLUSION: Famciclovir therapy decreases genital HSV shedding in HSV-seropositive persons, especially those with a history of genital herpes. Overall, antiviral drugs may have varying effects on symptomatic and asymptomatic viral shedding, depending on the clinical history of the disease.