Repeatedly negative PCR results in patients with COVID-19 symptoms: Do they have SARS-CoV-2 infection or not?

OBJECTIVE: To point out possible infection with SARS-CoV-2 in symptomatic patients despite repeated negative nasopharyngeal swab tests for SARS-CoV-2. MATERIAL AND METHODS: A retrospective observational study carried out at the Na Bulovce Hospital from the beginning of the pandemic until November 2020 included patients (1) who had symptoms compatible with COVID-19; (2) whose nasopharyngeal swab PCR tests in the presence of acute respiratory infection symptoms yielded two consecutive negative results; (3) in whom SARS-CoV-2 infection was subsequently confirmed by serology. Basic demographic and epidemiological data, symptoms, laboratory test results, X-ray findings and timing of virological tests were analysed for these patients. RESULTS: Seventeen patients met the inclusion criteria, 14 men and three women, aged 19-84 years with a median of 59 years, of whom 14 were hospitalized and three were treated as outpatients. Only seven patients were aware of the previous contact with an infected person. The main symptoms were fever, cough, headache, weakness, fatigue and shortness of breath. Pneumonia was found in 12 patients, four of whom developed respiratory insufficiency requiring ventilatory support. Most patients showed a uniform combination of haematological, biochemical and radio-logical findings: absence of eosinophils and increased polymorphonuclear/lymphocyte ratio; elevation of serum lactate dehydrogenase; elevation of CRP without rise of procalcitonin; typical chest CT or X-ray findings. All patients recovered. Coronavirus antigen test was performed in six patients, with all of them testing negative. SARS-CoV-2 infection was confirmed serologically by the detection of specific IgG and IgA in all 17 patients and also IgM in six patients, not before day 8 of the onset of symptoms. CONCLUSIONS: Our study showed that some patients with acute COVID-19 may test repeatedly negative by nasopharyngeal swab PCR. These cases should be interpreted as a low viral load in the upper respiratory tract rather than false negativity of PCR. Such alternative is not envisaged in the algorithms used. Considering our results, the following recommendation can be made: If, despite negative PCR tests, COVID-19 is still suspected based on clinical symptoms and epidemiological evidence, preliminary diagnosis can be made on the basis of comprehensive assessment of the laboratory test and X-ray findings. Final confirmation of the aetiology relies on serological tests performed two weeks after the onset of symptoms.

Antiviral prophylaxis of neonatal herpes infection.

Herpes simplex virus (HSV) is considered to be one of the most frequent viral infectious agents in humans. Transmission of HSV from mother to foetus during pregnancy is uncommon with about 85% of transmission occurring perinatally, when neonates acquire HSV during vaginal birth from infected genital tract secretions. For women, who present with an episode of recurrent genital herpes several weeks before the expected delivery date, suppressive therapy with acyclovir or valacyclovir is recommended during the last 4 weeks of pregnancy. The study group consists of 21 women with recurrent genital tract herpes, who delivered between the years 2007-2009 at the Department of Obstetrics and Gynaecology, University Hospital Na Bulovce. Women in the last month of pregnancy were administered prophylactic viralstatic treatment with acyclovir 3 x 400 mg per day orally until delivery. In this study, no patient showed signs of acute lesions and viral DNA was not detectable on PCR in vaginal secretions. One woman delivered by acute caesarean section following signs of foetal hypoxia during the first stage of labour, two women were delivered by forceps. No newborns showed signs of HSV neonatal infection. Antiviral prophylaxis in the last month of pregnancy in women with recurrent genital herpes infection is considered to be safe and effective in the prevention of vulvar lesions and in decreasing the incidence of caesarean sections in this group of women.

An attempt to demonstrate the increased resistance of selected bacterial strains during repeated exposure to UV radiation at 254 nm.

Evidence was provided that in a repeatedly irradiated bacterial suspension of Escherichia coli K12: AB 1157, 1886, 2463, under the described experimental conditions, gradually mutants more resistant to UV radiation survive. Under these circumstances it may happen that selection and an increase of bacterial clones with an increased UV resistance develop, manifested by a reduced effectiveness of UV radiation during repeated irradiation. Although the cumulating damage of DNA in microbes can lead to a reduction of their survival as well as a reduction of their absolute numbers, it can be hardly assumed that during practical use in air conditioning units or during disinfection of drinking water all bacteria will be destroyed. In that case even repeated UV irradiation is not necessarily a reliable disinfection tool.