Duration of MRSA colonization might be shorter than thought

The median duration of colonization with community-based methicillin-resistant Staphylococcus aureus (MRSA) in ambulatory patients is 21 days, shorter than the previously thought duration of 6 to 9 months, and treatment with clindamycin is associated with more rapid clearance of the infection, say findings of a study published yesterday in Clinical Infectious Diseases.

The authors, many of them from academic centers and hospitals in Philadelphia, carried out a prospective cohort study of 243 community-based patients presenting at any of five academic hospitals in Pennsylvania between Jan 1, 2010, and Dec 31, 2012, with skin soft-tissue infection (SSTI) that was found to be MRSA.

Patients and their household members (total, 803) performed self-sampling (or, for children, sampling by parents) from the nares, axillae, and groin for MRSA colonization every 2 weeks for 6 months. Clearance of the organism was defined as negative results in two consecutive sampling periods.

The median duration of MRSA colonization, defined as the period from diagnosis to clearance, was 21 days (95% confidence interval [CI], 19 to 24). In 19.8% of patients, MRSA had not been cleared at 6 months.

Clindamycin treatment of SSTI was associated with earlier clearance (hazard ratio [HR], 1.72; 95% CI, 1.28 to 2.30; P < 0.001). Older age was associated with longer colonization (HR, 0.99; 95% CI, 0.98 to 1.00; P = 0.010). An increasing number of colonized household members was associated to a borderline-significant degree with a longer duration of colonization of the index case (HR, 0.85; 95% CI, 0.71 to 1.01; P = 0.064).

The authors say future studies "should examine the predictors of persistent colonization, the impact of prolonged duration of colonization on development of MRSA reinfection, and the potential role of total household decolonization in adults and children" as well as further elucidate the role of clindamycin as treatment.
Feb 3 Clin Infect Dis study abstract

Trial: One dose of H3N2v vaccine immunogenic in most adults

An experimental vaccine provided protection against variant H3N2 influenza (H3N2v) after one dose in healthy adults 18 years and older, according to a study yesterday in the Journal of Infectious Diseases.

H3N2v viruses first emerged in 2011, but concern spiked in the summer of  2012 when the US Centers for Disease Control and Prevention (CDC) reported 306 cases. The incidence of known cases has since declined dramatically.

The study comprised 211 people, 104 of whom were 18 to 64 years old, and 107 of whom were age 65 and older. Researchers administered two doses of the H3N2v vaccine (15 micrograms of hemagglutinin per dose) 21 days apart to measure serum hemagglutinin inhibition (HAI) titers, neutralizing antibody (Neut Ab) titers, and memory B cell response.

HAI titers at or greater than 40 were present in 87% (95% CI, 79%-93%) of those under 65 and 73% (95% CI, 63%-81%) of those 65 and older after 21 days. HAI seroconversion occurred in 51% (95% CI, 41%-61%) of the younger group and 52% (95% CI, 41%-62%) of the older group, but neither seroconversion rate was statistically significant.

A Neut Ab response occurred in 91% (95% CI, 84%-96%) of the younger group, and 59% (95% CI, 49%-69%) of this group seroconverted after 21 days. In older group, 82% (95% CI, 73%-89%) had Neut Ab titers, and 67% (95% CI, 57%-77%) seroconverted after 21 days.

The authors said that, because 93% of the study population already had antibodies to H3N2v prior to vaccination, one dose of the vaccine should prove effective for a healthy adult population.
Feb 3 J Infect Dis study

Study: H3N2 viruses isolated from canine nasal swabs

Chinese researchers found two H3N2 influenza subtypes in pet dogs that contain both human and swine characteristics, according to a study yesterday in Virology Journal.

Researchers obtained 261 nasal swabs and 315 blood samples from pet dogs in eight Chinese provinces during 2013. After identifying influenza A canine isolate virus (CIV) in 35 nasal swabs from dogs in Guangxi province, subtyping showed the presence of H3N2 in two samples.

During subtyping, the viruses clustered with the human H3N2 Moscow/10/99 strain and most swine flu viruses. All blood samples were negative for CIV.

The findings suggest that dogs may be regarded as intermediate H3N2 hosts, even though the virus has not firmly established itself in canine populations, the authors said.
Feb 3 J Virol study