Pocket Medicine: The Massachusetts General Hospital Handbook of Internal Medicine (93 page)

If
all
the above met, NNT still 40–150 to prevent 1 case of Lyme (
NEJM
2001;345:79)

Regardless of Ppx, monitor for fever, flu-like sx, rash (erythema migrans) × 30 d

• Antibiotics:
if
clin. manifestations
and
serology (?
and
h/o tick bite if nonendemic area)

local or early dissem. w/o neuro or cardiac involvement:
doxycycline
100 mg PO bid × 2 wk (range: 10–21 d); alternative (eg, pregnancy, doxy allergy): amox 500 mg PO tid or cefuroxime 500 mg PO bid × 14–21 d neuro (other than isolated CN VII palsy), cardiac, chronic arthritis: CTX 2 g IV qd × 2–4 wk; alt (eg, severe b-lactam allergy): doxy 100–200 mg PO bid × 2–4 wk.

• Consider coinfection if severe/refractory sx, persistent fever, cytopenias

ROCKY MOUNTAIN SPOTTED FEVER (RMSF)

Microbiology & epidemiology

• Infection with
Rickettsia rickettsii
(Gram
obligate intracellular bacterium) • Transmitted by
Dermacentor variabilis, D. andersoni
(dog tick); peak in spring/early summer • Occurs in
mid-Atl, SE, Midwest
, New Engl, NW, Canada, Mexico, Central & S. America • Consider other rickettsial spp.:
R. akari
(Rickettsial pox),
R. conorii
(Mediterranean spotted fever),
R. africae
(African tick bite fever),
R. felis
(Flea rickettsiosis)
Clinical manifestations
(typically w/in
1 wk of tick exposure)

• Nonspecific:
fever
,
HA
, DMS, myalgias, N/V, occasionally abdominal pain •
Rash
(2–5 d
after
onset) =
centripetal
: starts on ankles and wrists → trunk, palms & soles; progresses from macular to maculopapular to petechial • Severe cases → vasculitis, hypoperfusion/shock, end-organ damage; more likely in elderly • Up to 75% mortality if untreated, 5–10% even w/ Rx (esp. if delayed) (
NEJM
2005;353:551)
Diagnosis

• Usually a clinical dx;
requires early clinical suspicion
given risks of delayed Rx • Acute illness dx by
skin bx
for rickettsiae (Se ~70%); 7–10 d after sx onset, serology

Treatment

• Doxycycline 100 mg PO bid
(give empirically if clinical suspicion)

EHRLICHIOSIS/ANAPLASMOSIS

Microbiology

• Gram
obligate intracellular bacterium;
human monocytic ehrlichiosis
(
E. chaffeensis
, HME);
human granulocytic anaplasmosis
(
A. phagocytophilum
, HGA) • Transmission: HME by
Amblyomma americanum
,
Dermacentor variabilis;
HGA by
Ixodes
Epidemiology

• HGA cases typically in RI, MN, CT, NY, MD; HME in SE, south central and mid-Atlantic • Peak incidence spring and early summer; can be transmitted by blood transfusion
Clinical manifestations
(typically w/in 3 wk of tick exposure)
• Asx or nonspecific: fever, myalgias, malaise, HA, cough, dyspnea; onset often acute • Laboratory: leukopenia, thrombocytopenia, ↑ aminotransferases, LDH, Af, renal insuff • More severe disease can occur with bacterial superinfection in HGA

Diagnosis

• Acute: intraleukocytic morulae on peripheral blood smear (rare);
PCR
; later: serology
Treatment

• Start Rx based on clinical suspicion; definitive dx requires PCR (may not detect all spp.) • Doxycycline 100 mg PO bid (often × 10 d); should defervesce in ≤48 h, else reconsider dx

BABESIOSIS

Microbiology & epidemiology

• Infxn w/ parasite
Babesia microti
(U.S.), transmitted by
Ixodes
ticks; also a/w transfusion • Europe & U.S. (more commonly MN, WI,
coastal areas & islands of MA
, NY, NJ, RI, CT) • Peak incidence June–August (
MMWR
2012;61:505)
Clinical manifestations
(typically
1–4 wk after tick exposure; <9 wk if transfusion)

• Range from asx to fevers, sweats, myalgias, & HA to severe hemolytic anemia, hemoglobinuria, & death (degree of parasitemia correlates roughly with severity) • Risk factors for severe disease: asplenia, ↓ cellular immunity, TNF inhib, ↑ age, pregnancy
Diagnosis (
NEJM
2012;366:2397)

• Clinical syndrome
+ blood smear w/ intraerythrocytic parasites
• Repeat smears (q12–24h) if sx persist despite negative initial smear • PCR serum if smear
and high clinical suspicion, serum IgG can help but some false

Treatment
(
NEJM
2002;343:1454)

• Atovaquone & azithro for mild/mod illness; clinda & quinine if severe (more toxic) • Duration depends on host; immunosupp Pts often need longer Rx • Exchange transfusion if parasitemia >10%, severe hemolysis or SIRS

TULAREMIA

Microbiology

• Infxn w/
Francisella tularensis
via contact w/ animal tissue, aerosol, tick/insect bite
Clinical manifestations
(typically w/in 2–
10 d of exposure)

• Acute onset of fever, HA, nausea; ulcer w/ black eschar at site of entry; LAN; PNA
Diagnosis & treatment

• Hazardous and difficult to Cx, alert lab. Serology
by wk 2. PCR by research lab.

• Streptomycin or gentamicin × 7–14 d; empiric Rx may be needed given challenges in dx

FEVER SYNDROMES

Temperature
>
101°F or
>
38.3°C

Diagnostic approach

• Thorough history including ROS, PMH/PSH, immunizations, including from childhood •
Fever curve
(consider holding antipyretics); less likely to mount fever if: chronic renal or liver dis., extremes of age, protein calorie malnutrition, immunosupp., steroid use •
Exposures
: travel, occupation or hobbies, animals and insects, sexual contacts, TB; consider age, geography, season and incubation time in relation to exposures •
Physical exam
: complete exam w/ focus on mucuous membranes & conjunctiva; cardiac murmurs; liver and spleen size; skin, genitals, lymph nodes, & joints; complete neuro exam incl cranial nerves and meningeal signs •
If rash
: location, duration, progression/∆ in appearance, was prodrome present