Multiple Sclerosis Journal - October 2017 - 1512

Multiple Sclerosis Journal 23(11)
Table 3. Adjusted rate ratios (aRR) for infection-related physician visits in people with multiple sclerosis as compared with controls.

All infection-related physician visits
MS population versus controls
MS population versus controls
stratified by sex
Males
Females
MS population versus controls
stratified by age (years)
18-39
40-49
50-59
60+
Five most common infection-related
physician visits
Upper respiratory tract infections
Infections of the urinary system
Infections of the skin and
subcutaneous tissue
Bronchitis and bronchiolitis
Pneumonia

Number of physician visits per
10,000 person-years

Model 1

Model 2

Model 3

MS population

Controls

RR (95%)

aRR (95%)

aRR (95%)

9659

7070

1.43 (1.37-1.49)

1.43 (1.38-1.49)

1.41 (1.36-1.47)

8511
10,034

5704
7531

1.65 (1.49-1.83)
1.37 (1.31-1.43)

1.70 (1.53-1.88)
1.37 (1.31-1.42)

1.69 (1.52-1.87)
1.35 (1.29-1.40)

9502
8498
9208
12,235

7878
6570
6355
7927

1.27 (1.19-1.36)
1.34 (1.26-1.44)
1.43 (1.34-1.53)
1.65 (1.52-1.79)

1.27 (1.19-1.35)
1.34 (1.26-1.44)
1.43 (1.34-1.53)
1.64 (1.51-1.77)

1.25 (1.17-1.34)
1.31 (1.23-1.40)
1.40 (1.31-1.49)
1.63 (1.50-1.76)

2248
1750
1262

2203
826
792

1.04 (0.99-1.09)
2.15 (1.99-2.33)
1.62 (1.48-1.77)

1.03 (0.98-1.08)
2.23 (2.05-2.42)
1.63 (1.49-1.78)

1.02 (0.97-1.07)
2.20 (2.02-2.38)
1.61 (1.47-1.76)

957
594

880
322

1.13 (1.06-1.20)
1.99 (1.70-2.32)

1.12 (1.06-1.20)
2.08 (1.77-2.44)

1.10 (1.04-1.17)
2.05 (1.75-2.40)

RR: rate ratio; MS: multiple sclerosis; SES: socioeconomic status.
Model 1: crude (people with MS and controls matched by sex, year of birth, and place of residence; no additional adjustments made); Model 2: as for Model 1,
plus adjustment for sex (except for the sex-specific models), age (continuous, except for the age-specific models), year of index date (1996-2001, 2002-2007,
and 2008-2013), SES (quintiles), immunotherapy use not specific to MS (yes, no); Model 3: as for model 2, plus adjustment for the number of comorbidities
(none, 1, and ⩾2).

hospitalizations for skin and subcutaneous tissue infections may relate to sensory loss, peripheral edema, or
immobility and subsequent pressure sores in the MS
population. While intestinal infections are often selflimiting for adults in developed countries, our findings
suggest they can pose a serious health problem in those
with MS. Bowel issues such as constipation or diarrhea
are common in MS, but it is unclear if these directly
increase infection risk. Alternatively, an intestinal
infection with consequent dehydration might be less
well tolerated by individuals with MS, resulting in
increased health care utilization.
Other common infections included urinary system
infections and pneumonia, which resulted in 2-3 times
more hospitalizations and physician visits for those
with MS compared to the matched controls. These
conditions are known to be complications in MS;
infections of the urinary system typically occur secondary to urinary retention and indwelling catheters,31
while dysphagia and reduced mobility might increase
the risk of pneumonia.32 However, we were unable to
find another study quantifying the considerable impact
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of these conditions on health care utilization in the outpatient care setting in MS.
Relative to matched controls, people with MS filled
between 51% and 61% more prescriptions for each of
the main therapeutic groups of antimicrobial drugs
(antibiotics, antivirals, and antimycotics); this observation is consistent with our findings regarding
increased physician visits for infection. With a rate
of 10.9 prescriptions per 10 PY for those with MS,
antibiotics were the most frequently prescribed antimicrobials. Notwithstanding the necessity for appropriate access to antimicrobials, it would be of value
for future studies to consider the broader health
implications of their elevated use in MS, such as the
impact on the microbiome, emergence of antimicrobial drug resistance, and elevated risk of more serious infections.33
Our findings showed important sex differences in
infection-related health care utilization. Hospitalization risk and physician rates were consistently higher
for people with MS compared to matched controls, but
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